Isn't a 3 inch exhaust overkill

[99gst]

The reason I ask is because even if you get a 3" cat-back and a 3" cat or straight pipe, the downpipe usually ends up being 2.5". Even the 3" downpipes start off at 2.5" and then expand to 3". Even if it was all 3" your O2 housing is 2.5" max.

My point is, isn't a chain only as strong as it's weakest link. If you have a 3" exhaust with a 2.5" kink somewhere that the exhaust will only flow as much as the 2.5" kink will allow. This is why we get mandrel bent piping instead of press bent. So why set up a 3" exhaust if its all going to start off at 2.5" anyway and will only flow 2.5" worth of exhaust.

If someone can logically explain why the above is wrong, please enlighten me.

[kris]

here's a decent enough analogy for you...imagine blowing out of a cone with an open top versus a cylinder of the same diameter as the cone's top opening. get it? The cone is MUCH easier to move huge amounts of air through, particularly in higher hp situations

your weakest link theory doesn't apply because we're not talking about using a 3" exhaust with a 2.5" muffler right?

<<kris

[blunttwister]

nicely put.

[roadpie4u]

I dont even have my turbo yet (getting a 2g in the fall) but I've heard problems with the stock turbo and a 3" exaust leading to wastegate problems and boost creep. Now this obviously could be countered by a better wastegate and/or a better boost control system then the dumb ecu - but still, the notion is slightly annoying. Granted, the 3" sound sweet as all hell and is a pretty cool thing to have - but if you think the difference in flow between a 2", 2.5", and 3"... the 2" has a 3.14sq inch flow, the 2.5" has a 4.90sq inch, and the 3" has a whoppin 7.07sq inch cross! That's more then twice the 2" piping on some of the lower end dsm's. It all depends on what you want with your turbo. I mean, what, a stock 2001 corvette runs like 12.8 seconds in the 1/4 mile with all it's glamour and glory, and some dsm's are trying to run 11's. Now I tell ya, the notion of running more then 20psi of boost is a cool thing, but it'll freak your engine out after using it a lot. Seals and all werent made for more then like 15 or 16psi. But hey, whatever floats your wallet, cause that's the deciding factor...

"I may be starving, naked, and homeless, but my DSM runs 11's in the quarter mile!"

[dyezak]

Just incase everyone forgot...there are O2 housing eliminators that are 3" too, so you kinda blow the whole "straw" "funnel" "cone" thing out of the water. Plus most O2 housing eliminators have a larger wastegate tube, flowing more air and thus eliminating dreaded boost creep with a 3" exhaust.

[greenstreak]

The other factor is they always say that you should work from the tail pipe towards the turbo. Using 3" pipes from the muffler to the O2 housing should be better than say, 3" from the muffler to the test pipe or something. Plus, a ported Lancer O2 will be pretty close to 3" from TRE.

[99gst]

I'm not convinced by the cone analogy because you can't get out more than you get in. If the cone is 3" in diameter at the outlet and 2.5" diameter at the inlet the most air that can flow through it is what the 2.5" inlet will allow.

OK, so you get an 3" O2 eliminator and remove the O2 housing restriction, now we are left with the last restriction; the turbine outlet. Aren't they generally 2.5" in diameter for your standard 7cm housing. So you have a 3" cat-back, 3" cat, 3" downpipe, 3" O2 housing or eliminator but you still have a 2.5" restriction at the turbine outlet which is the very beginning of your exhaust flow.

My point is unless its all 3" your exhaust will not flow 3" worth. If any part of it is less than 3" you are not getting the most from your 3" system, right?

[dyezak]

I wouldn't assume you are going to run a full 3" exhaust (turbo back) without having a pretty large turbo. The 7cm's ported actually come out to almost 3". So a ported 16g or larger turbo wouldn't have the problem of 2.5" turbine outlet...common, don't you think after all these years these cars have been in production all this would be covered. People aren't going to waist money for 13years, sooner or later someone will wize up...at least within 7years (hehe). Either that or we're a dumb society.

[4G63Rydah]

You're forgetting one of the most important rules of thermo-dynamics. Hot gases move faster than cold gases.......... This means that the closer you get to the engine the hotter the exhaust gas is. And the faster it is moving. When exhaust gas is that hot (probably 1200+ degrees at the o2 housing and in the front part of the downpipe) The gas is moving very fast. Also it is expanded very much. That means that the "small area" it is in causes it to be under a certain amount of pressure. And gases and liquids always want to move to an area of least pressure. Which in this case is the end of the exhaust. At that high of a temperature and under that pressure the gas is going to be moving very fast, so the small size is really not a restriction for it. Once the gas starts to cool down the diameter of the piping is now 3". This is done because at this point the gas is cooler, and it is moving slower. So now things do get a little restrictive so you make the piping bigger to make it easier for it to exit to atmosphere and also to decrease the pressure towards the end of the exhaust (remember, gases move from high pressure to low pressure). If what 99gst is saying was true. Then you wouldn't get a performance gain of an exhaust system that is bigger than the exhaust ports on the head...

[99gst]

So your point is you need a larger diameter the further away from the turbo's turbine outlet because the gases have cooled and therefore expanded. If the diameter is the same as it was at the beginning, then backpressure is increased because the gases have expanded but your piping has not.

OK, this makes reasonable sense and is the kind of explanation I was looking for. Thanks

[dsmntat]

You have it backwards 99gst. Think about it this way, in terms of water. In the gas state, it requires more space, less space in liquid and even less in ice.

As the exhaust moves futher from the engine it cools and comes more dense(needing less space), closer to the engine the hotter it is and expands more(needing more space). So have bigger piping closer to the engine.

This sound right to all you guys?

[4G63Rydah]

dsmntat you have it wrong. It's not about how much space it needs. It's about restriction. When the air is hot, it takes up a lot of space, and it will move vary fast. That means that a little restriction won't matter that much since it'll force its way through VERY quickly. When the gas gets colder, condenses a little, and slows down a little restriction is a BIG deal. So you want bigger pipes to reduce restriction as much as possible and create a lower pressure to allow the gas to escape.

[90tsi]

Here is a pretty good in-depth discussion awhile back about heat transfer and a whole lotta other stuff
http://www.dsmtalk.com/forums/showthread.php?threadid=3676

[99gst]

Originally posted by dsmntat
You have it backwards 99gst. Think about it this way, in terms of water. In the gas state, it requires more space, less space in liquid and even less in ice.



Fill up a glass of water and put it in the freezer. Tomorrow when its ice you will see that ice takes up more space than water. Why do you think unopened coke cans or bottles explode if left in the freezer too long.

Gas expands as it cools. Think of what a turbo does, it compresses incoming air. This compressed incoming air is then hotter than it was before it entered the turbo. If it wasn't we all wouldn't need intercoolers to cool it back down.

[dsm4eva]

Gases contract as they cool, water is the ONLY liquid that expands when it's state changes to solid and isn't a good analogy.

Ideally, on a turbocharged engine, the less opportunity for the exhaust to decrease the freewheeling of the exhaust turbine, the better. The 3" and larger exhausts are built for this purpose, to allow the denser and colder end of the exhaust system to flow easily and allow the turbo to freewheel to it's maximum capacity. The 4G63 really doesn't flow enough air to necessitate much more than a 3" exhaust system until you step up to the plate with a gargantuan turbo for pure race-bred applications and most of these cars will usually have short side exit pipes of a MINIMUM of 3" in diameter.

The exhaust system is comprised of a 'hot' end and a 'cold' end normally characterized by the temp of the exhaust gas. The 'hot' end on our car is basically the manifold through the cat. The 'cold' end is the cat back. This is the normal dividing line by OEM development and purchasing and fits into our discussion here as well. The way ideal to modify a turbocharged exhaust system is to work from the muffler forward, toward the engine :). Quite often, this is a PITA (pain in tha azz, for you non-IRC types) so usually most people will upgrade say from the cat-back and then the cat+downpipe, and finally the O2 housing (note: this is assuming staged evolution, not the all-encompassing-whole-system-swap type modding where you would go with the best of the best when possible). This staged swap will open the exhaust and allow the turbo to spool easier.

On N/A cars hot end will be the header, while the cold will be from the cat back. Changing piping diameter will directly affect the engine's torque response curve. Whereas, a turbocharged car receives its torque response curve based on the RPM and load generated by the turbo. So you can see, the N/A cars have to put a little more thought into this aspect of the system than we do. It is also why slapping a huge buzzing exhaust on a Honda isn't the smartest thing to do, and the average uninformed domestic V8 owner will tell you that you are dumb for having a huge 'coffee can' exhaust. Now you know the retort to both of these types of people.

As for needing an intercooler to cool the compressed intake charger, when you put work into the intake gas you are adding heat to compress it. This is the heat we must reject to make more power. When a hot compressed gas (like exhaust or our intake charge) rejects heat, it becomes denser. The process is nice for our intake and not so nice for our exhaust.

[Edited by dsm4eva on 06-20-2001 at 03:58 AM]

[roadpie4u]

listen to DSM4eva. If you dont believe him, just buy an entire 3" exaust setup and be done with it. But like he said, if you're running a stock turbo, you dont really NEED the 3". If you up the turbo and pressure in the engine, then get better flow out. Now, an after engine intercooler has not been attempted, because it gains us nothing. The only reason you intercool the air is so it'll burn better. If you cool the air on an FMIC, the hot air goes into your engine compartment, and that's not great, but it's better in the engine bay then in the engine. If we could keep the engine bay cooler by 50 or 100 degrees during a good run at WOT, we'd be good. Cooler means better combustion, more efficency, engine longevity. Like the radiator releases heat in there, the A/C releases more, the Intercooler even more. The steering fluid cooler, brake line cooler... then the turbo just lets off a crap load of heat. Then the engine lets off more... This heat is useless to us, we have no use for it, it is annoying and hampers engine performance, it'd be better to get rid of it. How? Get rid of your hood! Not likely. Hood vents? Perhaps. You know how the real Z3's have those vents in the fenders? You know why they orginally designed them annoying things? They originally had pipes going to the back of the engine bay, so air could blow out the sides (as well as the bottom under the car) and let hot air out, to let more cold air in! Dont cool air unless you're gonna get something from it. Period.

[Stephen]

just buy a 2.5" exhaust and then get your hands on some really cheap really good insulation that wont catch on fire then you have the flow of a 3" with the sound of a 2.5" but youll also have huge chunks of insulation hanging off your car, doh....

[kris]

Originally posted by Stephen
get your hands on some really cheap really good insulation that wont catch on fire then you have the flow of a 3" with the sound of a 2.5"

really? does retaining the heat help the flow THAT much?

what type of insulation are we talking about? header wrap isn't cheap and I can't think of anything else that wouldn't catch on fire under a car. I've got a 2.5" and I want a 3" so anything that would help me out in the meantime would be well worth the effort

<<kris

[BatmanGSX]

On a turbocharged engine as little exhaust restriction as possible is best, the turbo provides the necessary backflow for the engine so after than then nothing at all is best... So if you have a 2.5 inch 02 housing and a 3 inch exhaust is better than a 2.5 inch 02 housing and a 2.5 inch exhaust.

[Dj Eclipse]

at the track I've seen some guys take off the exhaust completly. This is much better than any exhaust..but does the turbo really provide enough back pressure not to harm the engine?

[NosLaser]

How about you just buy the 3 inch exhaust so you never have to upgrade again? Why spend the money twice? We ALL know the 3 inch is proven to make the most power, why start some silly thread on it's merit? We've heard it all before "a turbo car will like the largest exhaust possible that will fit under the car, and that your ears will tolerate." Obviously, up to a point, that is absolutely true. A 3 inch exhaust is about the biggest out little 2.0L 4 cylinders will ever need, so if you could fit a 4 or 5 inch exhaust system under the car, you wouldn't realize any power gains...BUT, you will not lose power either. People can argue this statement I am about to make till they are blue in the face, but NO ONE buys exhaust for their car and just leaves it that way. Sooner or later, you will want to go faster. Unless of course your pHaT aZz Bro-speed tip with the yellow insert is just fo' looks yo.

[99gst]

When I started this thread, I figured eventually a reasonable explanation would show up proving that a 3" exhaust is superior even in light of the O2 housing and turbine outlet restrictions.

I don't think its silly just to pose this question for debate. I'm not the kind of person that just accepts something is true or fact just because everyone says it is.
PROVE IT!

I know a 3" exhaust is better than a 2.5" exhaust. The heart of my question is the following. Assume your exhaust starts off as 2.5" then expands to 3". Why would a 3" diameter towards the end of your exhuast (cat-back for example) be better and 2.5" all around.

4G63Rydah says is thermo-dynamics and that seems reasonable to me. I thought this topic was over anyway.

[BatmanGSX]

Originally posted by 99gst
Assume your exhaust starts off as 2.5" then expands to 3". Why would a 3" diameter towards the end of your exhuast (cat-back for example) be better and 2.5" all around.

I already explained this. The less restriction you have the better. A 2.5 inch DP and a 3 inch catback has less overall restriction than a complete 2.5 inch system. You keep taking away restrictions and you will add power. So Stock sucks, complete 2.5" is good, 2.5" DP with 3" catback is better, full 3" is better than that and nothing at all is the best. There is no in depth physics about it, it's just as simple as less restriction is best.

And to the guy who asked:

You better beleive the turbo provides enough backpreasure. Have you ever looked inside a turbine housing? Necks down pretty good doesn't it? The whole 4cyl engine is forcing air through an area smaller than a 1cyl lawnmower exhaust.

[Dj Eclipse]

So that's a yes??? :D

[Zazzster]

Had to chime in and drop my two cents. There are certant headers out there that get smaller as they go. The idea is that as the air cools and contracts it will slow down if the pipe stays the same size. So if you gradually decrees the size of the pipe the flow of exhaust will remain at the same speed. If you thermal tape you whole exhaust, you WILL increase flow. By how much? Duno...
I have a full 3" with a stock 14b&O2 housing. So in my case 3" is overkill. (For now)

I think 3" system sound better.

There. That's my two cents......

[CobaltGSX]

the 2.5" o2 housing and and first step or width of most 3" downpipes is essential in the movement of colder gases in towards the end of the exaust....the smaller area and higher exaust temperatures are great for high velocities used to push the cooled gases out. the 3" is alot better. you said it perfectly with..

So your point is you need a larger diameter the further away from the turbo's turbine outlet because the gases have cooled and therefore expanded. If the diameter is the same as it was at the beginning, then backpressure is increased because the gases have expanded but your piping has not.

[V8SpankR]

I wonder how many ponies I'm losing going from the 2.5 inch dp into the HKS 2 3/8 inch? Actually it doesn't seem to be hurting too much 'cause I'm faster than a few others w/similar mods (16g at 17psi,stock IC and injectors) plus a 3 inch exhaust.

[kris]

Since containing the heat will increase flow what should I use to wrap the exhaust? I'm thinking header wrap on the manifold, turbine housing, O2 housing, and the downpipe to the flex section and then using that reflective heat protector wrap stuff back until the muffler. Can anybody think of reasons this won't work? The only stuff I can come up with is that it may work too well and crack the manifold. Also that reflective wrap may get really nasty and fall apart on me after a short time. Jet coating isn't an option, if I had that kind of $$$ I'd have bought a 3".

[Nick 92 TSi AWD]

Wow what a useless discussion. Honestly I don't see a <real> need for a 3" exhaust. I've tested two friends cars, one 14b one 16G. With no other changes other than their 2.5" turbo backs for my 3" turbo back, their was NO change in MPH AT ALL. It didn't make any more power. Spool up was slightly better and that's it.

Now what about a bigger turbo, say 20G, green, mutt <ack!!>, or g-pumper? Well you should have an external wastegate anyway <well unless you have the ultra super mutt> so the 2.5" isn't a restriction under full boost, you're dumping extra gas out the wastegate. One guy on nabr tested this, he has a 2.5" turbo back. Swapped to a 3" turbo back. NO MPH increase. Didn't notice any spoolup change either.

I got a better idea, buy whatever exhaust is cheap, put it on, and forget it. Worry about something that's worth worrying about, your engine tuning.....

[Le Talon]

I have to agree with this, cause I did the test last week at some import event. Keep in mind that my external WG is vented to the atmosphere, so a lot of the exhaust is coming out of the WG at WOT.

To make a long story short, I ran open downpipe. Car was running the same, same ET, same MPH. I have a 2.5" DP, TP and a 3" mandrel Cat-back with a not so good chambered Super Turbo Muffler. I have a Frank 3 turbo.

I'm guessing that the open external WG makes up for the lack of exhaust.

Last year, I did the same test with the 16G and the regular internal WG. Same results.

[greenstreak]

I can understand why a 2.5 dp would not be a restriction when running an external gate vented to the atmosphere but what about if you are running a larger turbo with an enlarged internal gate? Say a Mutt 3 with a 40mm internal (just for Nick ;)) wouldn't a 2.5 dp be a restriction for all of that exhaust gas?

[kris]

letalon and nick have convinced me to stick with my 2.5" setup and stop worrying about it. after all the biggest I plan to go is a big ported/clipped 16G. thanks guys

[jasen]

I did my whole exhaust, downpipe back at the same time. Full 3", all of it custom except the DP which I bought. I also already had a 14B on my 2nd gen by that time as well. (yes I know, it was backwards to do the turbo before the exhaust, but it came like that) I had them use a highflow 3" cat and no muffler at all. The difference with that exhaust was amazing. I think my spool time was halved. Well, it feels like it with my butt-dyno. :) I don't use a boost controller at all yet, and my max psi is right around 17 so far, without me doing anything to control it. So personally, I would say the complaints of excessive boost creep with a 3" exhaust are overrated. I really haven't noticed it yet. But the performance difference makes me recommend it.

[Nick 92 TSi AWD]

Originally posted by greenstreak
I can understand why a 2.5 dp would not be a restriction when running an external gate vented to the atmosphere but what about if you are running a larger turbo with an enlarged internal gate? Say a Mutt 3 with a 40mm internal (just for Nick ;)) wouldn't a 2.5 dp be a restriction for all of that exhaust gas?

Erik, please don't make me angry, you wouldn't like me I'm angry.....:) <ya know the incredible hulk>

Yes it would be a restriction for sure with an internal gate. My opinion is that 2.5" is fine for a 16g or big 16g, it's cutting it for a 20G. Anything larger than a 20G and you should be using an external <IMO> anyway. If you are using an internal with a larger turbo then I'd go 3".

That being said I have a full 3" turbo back....my new dsm <picking up a 91 this week, $500> will probably have one two; but only because I'm making it myself and my only jig is for a a 3".

[Zazzster]

Quote.

"So your point is you need a larger diameter the further away from the turbo's turbine outlet because the gases have cooled and therefore expanded. If the diameter is the same as it was at the beginning, then backpressure is increased because the gases have expanded but your piping has not. "

What????

Gas contracts as it cools. Please think about it.....

Backpressure may increase due to the fact that cool, more dense exhaust is harder to push along. That is why thermal tape is a great idea. Keeping the gasses as hot as possible keep the exhaust move faster...

Good point guys about the larger turbos requiring an external WG. Never thought about the extra pressure relief the WG provides.

[95TsiAWD]

Just go HRC 3'' Eliminator and Thermal 3'' catback and be done with it :) then you can be the envy of all your friends

[Rdy2race]

then your friend like me is laughing at you with your dinky oil filter and looking on holding my side an you burn your self once again on the DP! :D

Sorry had to say that..

Nick,
PROZAC PROZAC PROZAC

Now with what was said ( and NO I didn't read all of it!! HA!!) I agree and don't with a few things. But how about this. In a car you have a COMBO. A combo of parts. 1 part is not going to make a huige gain in any car ( to a point!! )For the most part Yes 3" is over kill but it also is needed for some others. With a 16G ( or turbos in that range ) it is not needed nearly as much with a car running cams, Huge T3/T4 8k+ redline and so on then Yes it is usefull. But when you have to give to get. Be it = a lot of money
= Spool time
=down low torque
= sound & volume
= major service hassel

you can get other things like
= stupit top end power
= smaller spool time
= more HP on the top end
= more sound!!!
= better service ability

so you have to weigh out what is best for your COMBO.

It's all about the COMBO not one part that is in the combo

Is is 3" over kill?? maybe so maybe not.

[99gst]

Zazzster, dude we already went over that point. I know gases condense as they cool, that was just a momentary lapse on my part.

Having started this thread, read all of the replies and researched elsewhere (including NABR) I concluded that a full 2.5" is enough to get an AWD into the 11s and a FWD into the mid to low 12s. That’s faster than most street driven DSMs anyway. If I wanted to go faster than that I would need a roll cage, scatter shield, etc. making it more into a drag strip car than a daily driver. If that were the case then I'd run no exhaust and be done with it.

The three main restrictions of the factory exhaust systems are;
1) 2" piping that is press bent and therefore flows less than 2"
2) muffler and resonator
3) catalytic

I will run a turbo back 2.5" with test pipe (no inspections or emissions here in Florida, gotta love it) and that will be all the exhaust that I need. There are a lot of gains just from running a straight through muffler and test pipe as these seem to be the biggest restrictions, especially the cat.

So I conclude a 3" exhaust is overkill for 95% of street driven DSMs.

Later

[Nick 92 TSi AWD]

TWEAK!!! :eek:

For simple power output <which is all I thought we were talking about> a 3" probably isn't needed. When you start throwing in spoolup and junk like that it just makes it complicated...:)

[v8_kllr]

i have to disagree with you guys that wanna thermal wrap your exhaust. your exhaust is one big heat sink-- it is gonna cool the gases on its own .your exhaust was intened to rid your engine of exhaust gas and heat. wrapping it would defeat the purpose of having the pipe there in the first place. if you want to keep heat in the exhaust, dont upgrade it. this way there is less metal to radiate heat. anyways, the wind moving below the car when you are moving will pull the heat away from the exhaust anyways.this this is just basic grade 8 physics. ...just put a 3" cat-back on and upgrade as required. its cost effective, and won't kill your powerband. it will also give you some decent gains with the supporting upgrades, i think anyways.

just my 2 cents. :P

[xxxxdmn]

Wow that was entertaining guys, thanks I thoroughly enjoyed reading that, honestly ;) I completely agree with the internal/external wg and b16g or < ideas. The thing is you never know when your going to want to stop.

With that said I have a small amount of real world experience comparing the best of the best vs the worst of the worst in exhaust upgrades. I had a wildly hogged out TRE o2 housing and a full mandrel 3" turboback with TP & straight through muffler on my br20g (td05h/~20deg clip) then while demodding the car I had a pressbent 2.5" turboback with restrictive $20 muffler thrown on it for $136 new including tax, labor, part shipping, and everything. Say 5ftlbs of torque gained before boost or so, whatever is the smallest amount you could just barely notice, put it that way. And say 5-10hp went bye bye up top over 4.5-5k rpm. The car had a 40mm hks gate on it at the time, after it got a s16g w/ stock wg & creeped a lil even on the 2.5" press but I ran 16-20psi on pump gas regardless with no problems, the car was quite a bit slower at this point but too much else came off the car to validly compare any further. It spooled faster with the ported & unclipped 16g on the 2.5 than with the 20g on the 3" but that's just due to the large clip on the 20g and slightly increased mass to get spinning, on the same exhaust they would barely be different I'm sure.

The main thing was spool, I lost ~400rpm with 2.5 press and a $20 restrictive muffler vs 3" mandrel and straight through. If I do another dsm it gets a 3" o2 elim dp & catback w/ tp + str8 through muffler and at least a fp green. The car would "snap" forward alot faster and harder with the 3" mandrel also.

Honestly... for $136 who really cares though? You could ghetto a 3" up for probably $175 instead if you wanted, and do weld in mandrel style for another $50. If I'm paying $ for prefab SS mandrel and its $150-250 more for 3" then it's a no brainer I think, $400 would make me opt for 2.5" and a 50shot or something more productive...

Local guy header wrapped his whole exhaust, it'll just make it brittle/ruin it in a year or so most likely. It might have given him some almost unmeasurable hp increase and helped spool abit, entirely not worth the effort though. I wrapped the first bend of my dp just past the oil pan however because I didn't care about the extra wear on the metal (Cheap RRE SS 1st bend). I can't say anything about hp or spool, but oil temps went down 10deg on average, your keeping heat away thats normally directly under the oil pan, for $10 in wrap it's a pretty cool/quick thing to do.

>[v8klr]
>1 4g63 motor = $3,000
>1 ported and clipped 20G = $2,500
>1 tank of race fuel = $50
>smoking every V8 on the planet
>PRICELESS!
Ported and clipped 20g for $2,500? You been shopping @ extreme motorsports again? hah hah

[v8_kllr]

nah. im in canada, magnus motorsports is in my backyard
hahaha

peace:D

[95TsiAWD]

Originally posted by Rdy2race
then your friend like me is laughing at you with your dinky oil filter and looking on holding my side an you burn your self once again on the DP!

Actually I find the filter much easier to change now than it was previously (and that's with the really big 1G filter). This is the older one piece eliminator downpipe, don't know if that makes a difference, I think HRC did an excellent job of leaving enough clearnace for the filter.

[Rdy2race]

easyer then stock?? umm... no, sorry but stock it a lot of room and allows for a lot of room around the pipe. Yes it fits but not with a big filter on a 1G it WILL pit the pipe in to the filter. with the WIX or other smaller filters that are like the 2G one will fit the 1g with some room but not alot. On a 2G a bit more room is found but not tons"

Having started this thread, read all of the replies and researched elsewhere (including NABR) I concluded that a full 2.5" is enough to get an AWD into the 11s and a FWD into the mid to low 12s. That’s faster than most street driven DSMs anyway. If I wanted to go faster than that I would need a roll cage, scatter shield, etc. making it more into a drag strip car than a daily driver. If that were the case then I'd run no exhaust and be done with it.


yes people have gone 11's on 2.5 " systems and more will. they will know the value of the parts and all have left the 2.5 systems for a better flowing system. Fast cars do not have Ehxt systems other then a pipe to remove the heat from the bay.

in short the major part of the world will only need 2.5 D.O.M. systems. 3" is a bit large and as for nick not getting any MPH out of the car this is B/C the LACK OF TUNING. you can NOT just slap on parts and look for gains. Now with that one of 2 thigns happened 1 the car was so well tuned with the 2.5 " systems and it was such a high flowing system that the gain in size didn't affect the car or 2 he didn't tune the cars for the new larger system. The reason I know that #2 is the right answer is B/c the car didn't suffer when the larger system went on. The idea is that with a larger system that the car will see less bacvk pressure on the turbine and allowing more flow. With a turbine housing and the wheel the motor has MORE then enought back pressure and with that being fed in to the 3" system it allows for a great pressure drop on the wheel and almost none on the other side of it meaning that the less back pressure the better the spool time. the heat after the turbine is not part of the deal since this will have little effect on the car other then spool time. the heat is not something that you want in the bay but in the pipe it self.

Kris to answer the Q you had. Hot paints like Jet Hot and others the HPC coatings will do the job that wraps do but with a mani like we have it is not the easyest to wrap.


BM-

[xxxxdmn]

General concensus seems to be it's a pita but stock stuff basically fits, your hair will just turn gray much sooner than normal. Some people say they need to remove DP to change oil filter, I'd find another filter.

My opinion is that once your to the point where a ported o2 housing doesn't offer the flow you need for your hp levels, ie. maybe deep 11 second car or faster you could just get a full garret turbo for $600-900 depending on wheels/housings/bb option + a garret DP flange, mandrel 3" bend and have a down pipe made for $100 at any local shop. It works out almost the same as getting a mitsu/garret hybrid and not needing a hks etc. garret exhaust mani. I've seen the HRC pieces and they look good but I looked at the price and then the part and was just thinking "righhhht" to myself :) Hey if you've got the cash!

Incidently there was a BR57 (full garret that buschurs orange car went 10.01 on), HKS cast exhaust manifold, oil line kit, downpipe flange, and deltagate w/ dumptube that went for $850 on ebay last week. That was almost tempting enough for me to scoup it and get another fmic/injectors/vpc/afc to remod the talon and get ripping around again even faster this time around... The fact that I've got enough headaches and don't need to add a blown 4g63 to them and that I've heard that BR57 kept seizing after repeated rebuilds for one guy and that buschurs like the only one running it made stay out of the bidding. 92 EPROM ecu went for $85 on ebay last week too, everyone should be scouring for deals constantly with stuff like this happening. Something like that might be a tad rough on the street spooling around 4500 or something I'd guess but for $850 and considering the top end who really cares?

All that stuff had *TWO* dyno pulls on it, that was it. Otherwise new. That's the kicker :-)

[easyer then stock?? umm... no, sorry but stock it a lot of room and allows for a lot of room around the pipe. Yes it fits but not with a big filter on a 1G it WILL pit the pipe in to the filter. with the WIX or other smaller filters that are like the 2G one will fit the 1g with some room but not alot. On a 2G a bit more room is found but not tons"]

[Tevenor]

Mmmm spool. Its what autocrossers dream of and drool over. Anything that allows more low end torque and less spool time is a good mod in Being able to drop ~400 rpm's between on-throttle and full boost is like being ablet to run 26 psi at the drags where you normally run 21. Yes it gives me a stiffy. Getting full T-25 boost of 15lbs @ 2200 rpms gives me wood. 3" exhausts with 02 dump tubes makes me dizzy.

I wonder if anyone has graphed exhaust flow rates based on displacement and boost pressure @ X temperature plotted against 2.5 and 3 inch flow rates with exhaust temperature and flow rates as parameters.

[augmach5]

A 3 inch dp will also cause u to lose some low-end ummmph,I noticed it even on a 2.5 inch dp, when using the t-25, I dont know if it really makes up the difference on the higher rpms,removing the cat sure help though. but dont tell anyone..shhhh. So if upgrading to a fp t-28 should i go with a stock ported 2g 02 or try and use a evo 3 o2? Im running a 2.5 inch dp with a resonated test pipe that i think necks down to 2 3/8 and then the apexi 3 inch n-1 system..

[xxxxdmn]

You've got absolutely no need for the evoiii o2, unless your getting an unported one for the same price as a ported 2g o2 or can figure out a way to sell your stock o2 or port that yourself after swapping on the evoiii one and make money or get it for the same price. If you can do it for the same price you might as well. You want to avoid getting a 2.75"-3" heavily ported evoiii o2 housing and then going to a smaller downpipe/catsection then to a larger catback section again etc. Going UP/DOWN/UP is pretty bad for flow, DOWN/UP/DOWN isn't so hot either. Keep in mind you'll need a different DP flange/gasket or to do some slotting with a die grinder/cut & reweld etc. possibly to make it all fit if you go evoiii. Your best bet is to get a used ported o2 housing from someone and then sell your stock one possibly porting it yourself quickly to learn for the same price or a very small loss, I did stuff like this and basically got a bunch of my mods either for free or got "paid" to upgrade, suckers pay for mods :)

Kris

[Rdy2race]

lose some low-end ummmph,I noticed it even on a 2.5 inch dp, when using the t-25,

there is no such thing as Umph with a T-25
heheh
<duck>

But really that is B/C the T-25 is not a big unit and really isn't going to take advantage of the larger pipe unless other mods are in place to make it all work like a COMBO (notice combo in another post ;-) ) The T-25 with modded W/G and the right intake pipes sizes and so on will have a HUGE effect on the other mods placed on it, If you just did the DP but still have all the crappy I/C pipes then this flex is killing the down low also. Replace them and you will gain what you think you lost but also gained on the top end.

The big 28 ( new T-28 from FP and it KICK ASS, just install our first one 2 weeks ago and it was very nice ) the car would be able to use the larger DP B/C of the larger turbine wheel can flow much more.


About the EVO housings. None is better for a cast housing. The cost is a bit steep but Vs. a SS o2 housing it isn't. A ported EVO housing can be 3" with meat to seal where a 2aG won't, the EVO also will make ANY DP that is made for a 1G/2G o2 housing push the flex in to the T case ( on a AWD ) and this stress on the manifold is not good when it's cherry hot. In all you should be moding/replacing the DP flange if not the whole DP so it is not stressing the manifold.

[SoFlaGS-T]

has anyone ever considered a 3" pressbent pipe? what do you guys think about that? who knows what the diameter at the bends would be? its so much cheaper for press bends, and besides, it cant get any less than 2.5 inches at the bends...

[xxxxdmn]

I had a pressbent 3", those bends are trash... get a 2.5" mandrel SS first bent from RRE http://www.roadraceengineering.com for $30 for the downpipe as well as a 2.5" SS flex section, then just finish it up in 3", that'll at least keep it spooling pretty good. You can get a couple 3" mandrel U bends from JC whitney or 90's etc. and have them welded in for the rear 3 or so bends, for the extra $50 that will cost vs normal pressbent scenario it's definitely alot cleaner and worth it, I resold my exhausts I made this way usually for 2x or more what they cost to make after using them ;)

Kris

[augmach5]

Rdy2race-

u can see my mods list,the dp isnt the only thing installed and it did lose some low-end ummph lets say the hit u get at 3,000 rpm maybe got shifted to around 3,000 rpm or so..just letting u know.

I know of others that went the full turbo back 3 inch exhaust when still using the t-25 and did not like the results. I think the 2.5 dp and 3 inch cat-back(test pipe) back exhaust works good on the t-25,i wouldant go three inch dp until fitting a larger turbo.

So anyone know what boost u can run on a t-28 without hitting fuel cut if stock injectors are used? 14-15 psi maybe? considering a re-wired stock fuel pump or aftermarket pump is used.

[xxxxdmn]

[lets say the hit u get at 3,000 rpm maybe got shifted to around 3,000 rpm or so]

Wow it moved it up that much huh? :)

As T25's are pretty much expendable pinwheels (laugh) I'd hope everyone would AT LEAST move up to ported manifold/14b/o2 & 2.5 turboback. I'd avoid doing DP twice at least and try to plan ahead as hard as it is sometimes too.

Kris

[kpt4321]

Just because the 3in Press bent DP only goes down to 2.5 inches doesn't mean it's going to flow good. First of all, I would think that it actually necks down to more like 2 inches at the bends. Second, even if it's the same diameter, press-bending does not make for a smooth flow pattern. All that turbulence is BAD for flow, do youreslf a favor and go mandrel bent.

Second, about the original debate: Going to bigger piping will ALWAYS help flow, as long as you're not changing from 3in to 2.5in every half a foot. A guy I know who is very knoweledgeable about these things actually tested a 2.5 inch straight pipe and a 3 in muffler that necked down to 2.5 inches at the entrance and exit, and he found that the muffler had LESS backpressure than the straight pipe.

Using the logic that you can only flow as much as the slimmest part in a chain: why do you want to buy upgraded intake pipe when something like the turbo outlet or mass airflow meter is much smaller? Blow through a straw, then cut that straw until it's only 1 inch long and attach a 1 inch diameter piece of PVC....yeah, it's easier, huh?

[xxxxdmn]

I don't have time or the inclination to explain this properly. Check out the dejon tool website or maximum boost (corky bell) if your interested in knowing why this is (partially) wrong. Your right about the 3" pressbent though, those bends suck bigtime because the pipe kinks, 2.5 press is really smooth/not as bad but 3" press will still slightly outflow 2.5 press I'm sure. 2.5 mandrel vs crappy 3" press would require a little more thought and maybe some math for me to come to a decision on, either way mandrel bends to cut/weld in are cheap.. usem.

Kris

[Using the logic that you can only flow as much as the slimmest part in a chain: why do you want to buy upgraded intake pipe when something like the turbo outlet or mass airflow meter is much smaller? Blow through a straw, then cut that straw until it's only 1 inch long and attach a 1 inch diameter piece of PVC....yeah, it's easier, huh?]

[kpt4321]

I think my previous post was confusing. What I meant was that, if you believe that a system is only as good as it's weakest link (or smallest pipe:) ), then why would you upgrade your intake piping to 2.5 inch when the outlet is only 1.5 - 1.75 inches? Just a sarcastic response to point out that bigger piping will have an improvement almost anywhere.

[xxxxdmn]

Ok so we already agree then, I didn't catch the sarcasm at first and thought you just didn't realize the combined effect of reducing pressure drop, bends/directional changes, and air turbulence on hp output.

[I think my previous post was confusing. What I meant was that, if you believe that a system is only as good as it's weakest link (or smallest pipe ), then why would you upgrade your intake piping to 2.5 inch when the outlet is only 1.5 - 1.75 inches? Just a sarcastic response to point out that bigger piping will have an improvement almost anywhere.]

I'd love to see a 14b car with just an intake/2.5 turboback/exhaust side of head only ported & mani+exhausthousing+o2 all matched w/ 2g 8.5:1 pistons. Thing would probably have some pretty kickass low end, doing the same thing to a 2g even moreso w/ their head/intake.

[blazinmaniac]

well i have a pressbent 3" on my 1g fwd, and it is shit. there are more kinks and wrinkles in it than my ball sack. im going to dump it as soon as i can afford a new muffler.

[dsm1995gst]

Originally posted by blazinmaniac
well i have a pressbent 3" on my 1g fwd, and it is shit. there are more kinks and wrinkles in it than my ball sack.

:eek:

[xxxxdmn]

Aside from the other personal problems sounds like lifes got you down ;) I wouldn't really expect any noticeale improvement unless the things running good & >110mph.

[as soon as i can afford a new muffler.]


:eek: :eek: :eek: :

[EuroGSTSpyder]

Ok..I have read EVERY post in this thread..( YES I HAVE*lol*) and I agree with some and some I dont agree with..BUT...My Q is this:

For the stock turbo its fair to say you can stick to a 2,5 fulls ystem max...right?
I am going to put on a bigger turbo..not huge but bigger..similar to a big16g I guess...should I then go all the way to a 3" or will a custom ( i know a guy who lives of doing exhausts...best company in Sweden) 2,75 be enough? I think it will....
3" might get too big for a medium upgraded turbo and 2,5 is too small when rest of upgrades comes along.If I now put on the 2,75 with stock turbo...will that affect my present performance or help it up a little?
Then when I put on the bigger turbo and other mods will the real difference be noticed then?or will the 2,75 be to small?Of course its mandrelbent al the way..:-) and high flow cat...

Dont flame me for asking..I am still learning and this was a good thread about this IMO....
:P

[xxxxdmn]

I'd get one of these now if I had a 2g. It went 11.8 @ 119 on a full weight 2g @ 21psi. If rob says it did then it happened, it's a reputable shop.

http://www.forcedperformance.net/dsm_turbo_big28.htm

$750 w/ core & $900 straight up, $95 more for porting.

You can't screw with that really as it's a direct bolt on for a 2g and will keep the car looking stock much to the bewilderment of everyone you slaughter and the mitsu shop tech's who don't void your warranty when you come in with a blown tranny.

2.5 mandrel is plenty for all of it , but going 3" on the catback with weld in bends is a no brainer like I said before, it's so cheap it's not even worth thinking about just do that. A cat is also a no brainer, as in you have no brain if you get one and can get away with not running one by any possible means :P It's not so much the turbo you pick but your entire setup that would determine if 2.5 was a real bottle neck on your car. If you have a massive and cold intake charge @ high boost (read big turbo, fmic, >~20psi) and are going to actually tune it then the 3" would be better, otherwise it's not worth shelling out for a 3" mandrel ss unit probably. If $1k is pretty trivial to you (it is to me) then just grab the 3" mandrel (I would) even if you don't need it. It's loud and sounds mean, and you'll never need anything bigger, besides for resale purposes it'll be easier to unload probably too.

Any exhaust will help the T25 out, 3" won't do anything vs 2.5" however IMO, maybe a couple hp on the top end traded for a few ftlbs on the low end at best, the torque/hp curves would be damn close at any rate. Skip the hfcat if you can, your better off just running a straight pipe and bolting the stock cat in (cut and reflange it like the straight pipe so you can swap them) for emissions day. Then put it back on the floor of your garage where it belongs the other 364 days of the year :rolleyes:

Kris

[EuroGSTSpyder]

well I am curious..they say they use the modified t25 compressor and housing...Exaktly what is done to it?If it uses the t25 housing I can let a turboshop here mod it to be similar to that one...Dont need to ship back and forth over the ocean ya know?*S*


Wheel size? ported housing?

[EuroGSTSpyder]

hmm..cant edit above post anymore..

I just wanted to clear that of course I dont think FP will let anyone know what they did to their FPBigt28..I was talking in general here..*S*

[xxxxdmn]

well its obviously just a bigtime machined and ported exhaust + compressor housing stuffed with new allied signal/gtxxxx wheels from the new line of turbo's. I couldnt say what wheels/trim but figure it flows in around 550-580cfm or so, if it was anymore it would be compared to a 20g I would think instead of a b16g. I'd stick with FP, rob knows his sh*t and is great to deal with, local shop would be much more sketchy and it would be a hit or miss guess on the wheel sizing etc.

Kris

[EuroGSTSpyder]

ok..might talk to Rob then and se if he can help me out eventhough I live overseas...Cant get DSM parts here ya know....:-(

[piercedjd]

this whole discussion is too long, too old and too overrated. Hot Gasses move faster through a tube because they are trying to expand, plain and simple. this is why 2 stroke engines use expansion chambers and those tiny exhaust tips, once the exhaust has expanded and cooled it can flow easier through a smaller diameter tube. Let me throw something into you alphabet soup here. for a street car, why not run a big nasty turbo 3" O2 eliminator 3" downpipe, and 2.5 cat back........ by the time the exhaust has traveled to say the rear of the drivers/passengers door, the temperature change is so drastic that it doesn't require that huge ass pipe. you can then get all the desired effects ( faster spool and more exhaust flow) without the undesired ( cruising rpm drone and tickets for DB levels)

just my .02

flame away

[xxxxdmn]

Sup jd ;P

No argument, just doesn't seem natural so I don't see anyone doing it. Although there is some crazy WRX with a 4" "o2 housing" and 3.5" DP + 3" catback, it's a racing shop and a customer car so it looks like they did exactly what your describing. Where I live I'd rather have it mean sounding, either by droning 3" or f16 style 46mm tial, either one will do, external isn't always being obnoxious so a quiet exhaust w/ one would satisy both things for me I think.

Kris

[92awdLaser]

Wow, somebody is backwards here. I find it quite amusing to hear DSMers say that changing diameter from smaller (2.5" at the DP) to larger (3" at the catback) helps increase exhaust flow, while all the WRX people seem to agree that going larger to smaller is better for flow :) In fact, TurboXs, which is one of the most reputable WRX tuners has designed a system that begins with a 4" DP that tapers to 3" at the end of the downpipe, then has a 3" pipe (that includes the cat) that eventually tapers down to 2.5" at the "axle-back" section. Also, this system has been dynotested to supposedly produce the best exhaust flow (for a street car at least). To me, this makes sense, since the exhaust gasses are hottest in the beginning (and thus expand more) which will benefit from a larger area to help flow more. As the exhaust cools and condenses, less area is needed and thus the reason for a smaller diameter pipe. WRX tuners agree that if the diameter increases at the end of the exhaust path, the cooler gasses will flow with less velocity (since the gasses have condensed), and therefore reduce power (BTW, exhaust VELOCITY is what's is most important here, not necessarily back pressure). However, the issue with DSMers seems to be fighting the inherent boost creep that plagues those with small turbos and large downpipes, and also the cramped location of the DP and the oil filter. WRX's do not seem to suffer boost creep like DSMs, and the oil fliter is located far away from the DP, so this is probably why WRX owners use larger DPs. FWIW, I'll probably buy the TurboXs exhaust when the time comes (although there is someone selling a week-old catless SS 3" turboback exhaust on i-club for $500. Ahh, the choices :) ) Later guys.

[piercedjd]

92awdLaser: Isn't that what I already said?
:rolleyes:

[dsm4eva]

Things you do on the farthest end of a muffler system have the most direct effect on decreasing backpressure. A larger muffler will decrease backpressure more than a larger downpipe. So in essence, you have this backwards.

How would I know? I develop exhaust systems for a living.

[piercedjd]

I am not bying that on a dyno a 3" non restrictive blow thorugh muffler is going to produce any more power than a 2.5" non restrictive blow through muffler if both cars were equiped with a larger O2 housing and downpipe. sorry, just not buying it. If anyone wants to step up to the plate here and provide REAL dyno numbers from a back to back comparison you might convert me.

[augmach5]

It sure would be nice if manufacturers would provide flow data with there exhaust systems,but that would be in a perfect world and ours is not. But some food for thought most of the top 4 stroke motorcycle exhaust set-ups use a smaller diameter hedder then the pipe gets larger has it nears the muffler. This same technology might be similar to what a dsm turbo car needs, Im not an expert,it would just take alot to convince me using a large downpipe then running smaller piping in the rear of the car would provide a benefical result.

[piercedjd]

apples, and oranges....... Motorcycles, of the street variety are N/A first off, Secondly they are making peak power at around 14k rpms..... The diamaeter of the pipe is obviously going to get larger, that's called a collector, and the point where it is the largest would about the door on your car if the engines were placed side by side. Like I said in my first contribution to this thread, this discussion is boring outdated, and overrated. You are all going to run whatever you think makes more power or sounds coolest, so why does this topic rehash every couple of weeks?

[xxxxdmn]

Yah stop rehashing :P

I'm just seeing if anyone possibly has a SS polished canister style 2.5" or 3" muffler used or new for sale or knows the best place to get one cheap cheap. I could give slightly less than a f' about the brand name or it's supposed sound quality or any other such nonsense. I just want it shiny and to make the car look like it's got a $1k exhaust system on it :P It's for a $1250 1g fwd that already has a buschur 2.5 press downpipe that I just want to rig up a 2.5 press catback on & eliminate the cat in the process once it's through emissions, another 15hp wouldn't be bad and I want it a little more agressive sounding then that's it for mods on this thing just about. So with that said it's only gotta last a couple years at most. I know one of you has a line on some shiny junk muffler that will fit the bill here.

Thanks,
Kris

[TALONTED TURBO]

Im gonna answer the question to the guy who started this post which I think no one answered. HE said why bother with 3inch if your exhaust starts with a 2.5 part in your downpipe. Well, 3inch DOES HELP even if you have a 2.5 FULL downpipe then go 3inch catback... why because as your exhaust gasses are traveling back they get cooler, and when they get cooler, the EXPAND, which means having that 3inch in the back is a benefit. IMO, just get full 3" turboback from the start, I got 2.5 mandrel bent catback on there now and Im pissed because im going to a bigger turbo and now i need the 3"!

*my sig, the 3" Apexi is coming!*

[v8_kllr]

i think you mean when the gases are HOTTER they EXPAND. Wehn they COOL they are CONTRACTED. this is one of the reasons why 3' turbo back is better.from what i know,
having 3' turbo back eliminates boost creep, and allow the exhaust gases of the turbo to have increased velocity of the expanded gases, which require more room, in a sense.
this, will in turn, allow for the new gases to enter the 'emptied' area faster, alllowing for less boost creep(a backup of exhaust gas, IMO.) 3' cat back allows for the exhaust system to be under less stress or pressure when you are running at increased boost levels.

Just my little piece.:D

BTW, you might wanna turn down your boost, TALONTED TURBO.
18psi on stock fuel system(according to your mods list) isnt the best for the pistons. the most boost you can run is 14-16psi on stock fuel system. just thought i'd let you know. :P

-Deep

[TALONTED TURBO]

Ops I forgot to mention in there I have an upgraded fuel pump!
I was still running 18psi on the stocker though lol.

[v8_kllr]

isnt that, like BAD for the piston rings? i get paranoid when i spike at 16psi! i turned my MBC down till i get my rewire/pump done. i got soo paranoid i drilled holes in my downpipe( at the restrictive bend we all know about) to help eliminate boost creep.....it worked to some effect, kinda ghetto if you ask me. but hey, it works for now, right? now milegae is hit cause of all the turbulence those holes are making, but no more boost creep! back to beating Hondas....one jackass at a time. hehehe




-Deep

[flubyux2]

wow, there is alot of talkery about this subject. so much so, that i didnt want to read it all. haha, and it was funny when that one guy, said gasses expand as they cool. "notice, i dont say Liberry, or TOmorry anymore"

if its already been said, then i will re-iterate it. if it hasnt been, then take notice.

according to corky bell, the exhaust need only be about 10% lager than the outlet of the turbine.

for the "cone" and "straw" theory, it is definitly water-holding. remember, air has friction you know. and it doesnt just flow straight thru. it has Turbulence too. the air doesnt flow the same speed thru the pipe. the air is slower near the walls of the pipe, (due to the friction) and faster throught the center of the pipe. if you have a larger pipe, then you have a lager area of the pipe that the exhaust can flow quickly through, rather than get slowed down by the pipe walls.

since the air (exhaust) is slowed down by the pipe walls, and moves more quickly throught the middle, is a turbulent flow. if you could see the air, it would look MUCH like a lava flow. a new "front" of the exhaust pulse would continually reveal itself while the exhaust near the pipe wall would remain behind the faster-moving "front". its hard to explain, but next time you watch TLC and underwater lava flows, think of it as air moving through a pipe.

thats why a cone will flow better than a straw, there is less friction.

i either just added fuel to this fire, threw sand on it...or just pee'd in it.

enjoy
chris

[ouSeven]

i get paranoid when mine would spike at 22psi, i ran 20 at the track, and got 12.9 with just fuel pump. now i get paranoid when it spikes over 26psi ;)

-dave

[v8_kllr]

so is 3"inch exhaust ok for a 14b?(turbo-back?)

[flubyux2]

yea, but you ahve to upgrade to the 2G o2 housing in order to have a 3" dp flange to bolt to. i have a 1g, and the biggest i can fit on it is 2.5"

[v8_kllr]

ok.....one other question....how do you knwi t your turbo oil seals are going? i seen a couple of blue puffs of smoke today(burning oil)...........just curious...

-Deep

[flubyux2]

your turbo oil seals are probably going when you hit the middle or upper rpms.

cuz at idle, the oil pressure might not be enough to force the oil past the seals. but as the RPMs go up, so does the oil pressure, and the chance for oil getting past the seals..

another possibility is that the oil IS leaking past the seals at idle, and sitting in the Turbine, and when you take off, the exhuast gets hotter, spins the turbo and burnes the oil in the turbine housing creating a puff of blue smoke.

another thing it could be is piston rings. do a compression test to make sure that you do not have excessive cylinder blow-by. thats harder to fix than turbo seals.


it all depends on WHEN your car makes the smoke.

does it make it when you let off the gas
does it make it when you take off
does it make it after you have taken off
does it make it All the time
does it make it in here
does it make it in there
no i would not like green eggs and ham

[v8_kllr]

the oil burns slightly at hig rpms....6k to redline
i tooped up the oil(castrol 10w40 conventional) and put some Luicas Oil Stabilizer in. probelm stopped.i guess things like this are to be expected...the car is coming up on the 11 year mark.
should i switch to mobil 1 synthetic 15w40? maybe the conventional oil sucks donkey ass cause the turbo just kills it.

any thoughts?

Thanks in Advance






-Deep

[11seclaser]

Check out www.RnRRacing.com for the lowest prices on exhaust systems. RnR makes 3" 02 eliminators and real 3" Downpipes and exhaust systems.

[novaboy]

think about the funnel and the tube again.the area at one end times the speed at that end is proportional to the area at the other end times the speed at that end. the funnel will have a faster air velosity than the cylender. as the air moves through the exhaust its velosity will slow as well. so it is ideal to have a "funnel" type exhaust so that as the gasses slow there is more space for them to take up as to maintain an equal velosity.

[novaboy]

as the gasses cool there gonna be moving slower so they need more space to plow through so they dont restrict the hotter gasses behind them

[flubyux2]

nova, sounds good to me. as the gasses cool they become more sluggish and cumbersome, so the bigger pipe lets them Plop out, and the hot gasses pulse behind them.

Deep, keep in mind that some/most synthetics are also detergent oils. so if youve run dino goo for the life of the car and switch to a Syn. then the gunk and sludge that has built up around the old leaky gaskets, sealing them up, will be dissolved. in essence, the dino goo gunks up the cracks and leaks and seals them. then if you switch to a detergent oil, or syn. (has smaller molecules or something like that) it will dissolve the dino-goo-seal and then youll discover new leaks.

[FOGdarter]

Originally posted by xxxxdmn
I had a pressbent 3", those bends are trash... get a 2.5" mandrel SS first bent from RRE http://www.roadraceengineering.com for $30 for the downpipe as well as a 2.5" SS flex section, then just finish it up in 3", that'll at least keep it spooling pretty good. You can get a couple 3" mandrel U bends from JC whitney or 90's etc. and have them welded in for the rear 3 or so bends, for the extra $50 that will cost vs normal pressbent scenario it's definitely alot cleaner and worth it, I resold my exhausts I made this way usually for 2x or more what they cost to make after using them ;)

Kris

now this is logic. andgood direction to buy what you can't easily make.Spend your savings on a mig welder, make up 2 at same time end up with exhaust and free mig welder to make up all sorts of stuff,. You are working on your own car right?
heres one comparison of interest to at least me.
2.5" tubular o2 hosing with ext dumpCOMPARE TO
3" o2 eliminator with internal seperate path waste dump?
which is higher flowing and at which points of operation?

[FOGdarter]

Originally posted by dsm4eva
Things you do on the farthest end of a muffler system have the most direct effect on decreasing backpressure. A larger muffler will decrease backpressure more than a larger downpipe. So in essence, you have this backwards.

How would I know? I develop exhaust systems for a living.

if this is so and i can't chalenge it, then what is the design intent with the WRX? some exotic need to raise backpressure for tuning- which is another critical but unmentioned aspect of two stroke expansion pipe design

[flubyux2]

just get the biggest and shortest pipe possible. turbos dont need back pressure to operate, they dont really want any pressure at all.

and a Pressbent 3" is just as good as a Mandrel 2.5"... mainly because yoru exhaust is only as good as the largest restriction. so if your 3" DP is crush/press bent and the innerdiameter goes down to 2.5"... what was the point? you shoulda just saved yourself the trouble and got the 2.5" mandrel.

and if i hear anymore talk about how a smaller pipe is better for scavenging and what not and that it makes more power... im just gonna have to recommend you telling that to Buschur, MachV, ForcedPerformance, Road Race, Titan motorsports, GReddy, HK$, A'Pex-i, and so on and so forth.. whens the last time you heard someone brag about massive gains from going from a 80mm pipe to a 60mm pipe??? Bigger exhaust on a turbo application is like an FP Green or Red: they dont ahve to explain themselves and get all technical, they just work cuz they are PRUVEN!

yea, thats what i thought.

[scotthidley]

FOG here's the logic to size and flow.

Right at the turbo is the hottest exhaust gasses (talking from there til its out of the car). As the gases cool, the speed that they flow at slows down. So increasing the size of the tube/muffler whatever allows an increased flow.

So a 2.5" o2 can actually outflow a 3"muffler with a big enough temperature drop. I'll let you play around with thermal dynamics to figure out what flow rate and temperature drops are required to do so.

Also if you want to improve flow even more, you can get ceramic coating and/or exhaust wrap. Either of these will help the heat "exaust energy" stay in the exhaust, and therefore keep the flow faster.

Now Subura doesn't use a seperate channel from their wastegate and turbine exit. Some people are looking for downpipes that do this. There is a mixed logic on which one is better (even in the dsm world). A perfect example of this is looking at Extreme's ported 02 housing (which has a half moon cut into the entry side of the o2). This is the only dsm vendor I know of that does this. I believe the logic they are using is that they are increasing the turbulence on the exhaust side and increasing the flow of the gases that way. I stayed away from this logic and stuck with seperate passages. I did shorten the length of the sepearations though at the exit side of the o2.

I have plenty of porting pics posted on here if you would like to search for them and reference what I am talking about.

As far as dumped or not wastegate. Look at the hole diameter of the gate and add that to the area of the turbine exit. A 34mm flapper will usually have ~ 28-29mm passage. That area plus the 2.5" area of the turbine exit will still be less than the area of a 3" hole.

If you look at a turbo housing and an o2 housing, you'll notice you can't go much larger than 2.5" with keeping a seperate wastegate passage as well.

[AWD92TalonTSi]

here's my take on exhausts. i'm fresh outta my fluid mechanics class so here goes.

our end goal here is to create as much flow as possible. we acheive this by using bigger pipes and less restrictions. the comment isnt " a chains weakest link determines its strength" doesnt apply here and i'll show you why.

our basic equation is:

P1/y+(V1^2)/2 + Z1 = P2/y +(V2^2)/2 +Z2 + hL

where
P1= initial pressure (intial are at DP entrance)
V1= initial velocity
Z1= initial height
y(gamma) = specific weight (property of the fluid)
P2,V2 and Z2 are all final values ( at tail pipe)
hL is head loss
and hL= (KV^2)/2g where V is average velocity in our pipe and g is acceleration due to gravity. and K is the sum of all restriction factors. ( a valve may have a value of 5, or a small bend .5)

we can get rid of a few things
Z1 and Z2 because our change in height is minimal. and P2 because the tail pipe is at atmospheric pressure 0 psigauge.
we can also assume that V1=V2 due to mass conservation what comes in must leave and with only one inlet and one exit they should be about the same speed
so we are left with :

P1/y=KV^2/2g
manipulating this gives us

(P1*2g)/y= KV^2

still with me?
the term on the left is just a number and, if we want V to be high we want K to be low.
(K is actually the sum of each restrictions K value)
now to sum up everything and actually make a point.

every restriction in our system has a K value. so if you have a 2.5" restriction in your 3" exhaust it doesnt make the whole 3" system point less. it will flow a little less. but not enough to go with a whole 2.5" system.
i hope it all made sense

bryan

[16g-95GSX]

Sorry guys I got to page two and got bored from the constant monotonous arguments being made. Anyway, here's my input. I used to have a greddy SP catback when I first got the car. I have a 2.5" testpipe and downpipe put on. Now the SP catback is 60mm meaning about 2 3/8", and I finally broke down and swapped it out for the thermal. At the time I didnt have my injectors, Safc, translator, and a few other small odds and ends, but I have to say it made a night and day difference. The thermal R&D catback necks down just as it bolts up to the stock cat, so it blows there, and I'm probably going to have that piece chopped off very soon, but I can honestly testify that I got very increased results having swapped the two catbacks. In fact they were good enough to give me rediculous boost creep which I was forced to fix with a 34mm internal wastegate upgrade. I dont see what the big argument with the "3" is overkill" statements, as I say screw it, get a full 3" and be done with it. If your goals arent anything major but the basic mods, and you KNOW taht you will never go any further, then fine stick with the 2.5-3" catback setup, and be done with it, but if you have ANY hint of wanting more then get the full 3" setup. If you get creep, that sucks, get a 34mm wastegate and fix it for 30 bucks, but you might as well go all out and get the 3" turboback and have the proper setup from the beginning even if you dotn NEED that kind of flow with your current mods, its better than trying to get a new setup down the road and selling your current one. Do it once and do it right.

My concern however is noise with the full 3". My current setup is quite loud, nothing rediculous, but I can imagine the drone at part throttle with a full 3" turboback, so I'm interested in the comments on that end.

[Tevenor]

Originally posted by 16g-95GSX

My concern however is noise with the full 3". My current setup is quite loud, nothing rediculous, but I can imagine the drone at part throttle with a full 3" turboback, so I'm interested in the comments on that end.

Build it yourself and you can tune the exhaust like you would an engine. I have 2 bullet style mufflers in line with a Dynomax tail muffler. Full 3" from the o2 housing all the way to ther tailpipe. I can roll a golf ball from the turbo to the tailpipe and it will never get stuck. However it is the quietest 3" at idle I have ever heard and there is almost no drone above 3k RPM. I plan on cutting it up and adding a 3rd bullet muffler to try to kill some 2500-3000 drone. At WOT its loud but then again, it should be. :)

[dsm4eva]

Originally posted by FOGdarter


if this is so and i can't chalenge it, then what is the design intent with the WRX? some exotic need to raise backpressure for tuning- which is another critical but unmentioned aspect of two stroke expansion pipe design

Actually it is more likely the need to pass Federal Pass-by Noise regulations. The maximum Federal mandated dB level must be met at Federal test locations in Arizona and California before a vehicle is allowed for general consumption.

Restrictions in an exhaust assembly is the cheapest way to reduce sound. The trade-off is engine performance. Instead of making the financial decision to tool up a muffler line the component supplier for Subaru (ArvinSango in Osaka JP) most likely suggested dropping pipe gages at the muffler and/or using a current muffler design cross-section.

[scotthidley]

.Originally posted by dsm4eva


Actually it is more likely the need to pass Federal Pass-by Noise regulations. The maximum Federal mandated dB level must be met at Federal test locations in Arizona and California before a vehicle is allowed for general consumption.

Restrictions in an exhaust assembly is the cheapest way to reduce sound. The trade-off is engine performance. Instead of making the financial decision to tool up a muffler line the component supplier for Subaru (ArvinSango in Osaka JP) most likely suggested dropping pipe gages at the muffler and/or using a current muffler design cross-section.

Pass by only applies to new vehicles. I like the "most likely" suggestion. A company can offer any type of advice to any other company, regardless of where it is, or who they are;).

From the little calculation above, the entrance and exit velocities are not the same. The volumetric flow would be close to the same (denser at lower temps, would have the exit volume being slightly less). With a larger exit, the velocity would be less as well (while still flowing the same volume).

[DJpowerHaus]

What about the scientific method? How about some dyno sheets.. not just peak HP either. A controlled environment with quantitative data!

And what are you aiming for? More flow or more HP? Looks like everyone aims for the former... when they actually want the latter.

[a_santos]

3" is not overkill. 5" is probably overkill unless you have a diesel truck. Generally speaking on a turbo car, you want exhaust as big as possible. And as a bonus your exhaust will sound better. I am not saying get 5" exhaust, but 3" is pretty reasonable. I have a ported o2 housing and a 2.5" dp and cat, and then 3" all the way back to the muffler. I wish my cat was 3" as well, but I got a good deal on it. So, spend the extra money and get 3", you will not regret it. Just make sure that you have enough ground clearence. I have never had problems with my car.

[gdmbat85]

ok im not gonna read all 5 pages so incase no1 has said it... heres the reason why 3" is better than 2 1/2" all the way. air resistance. the air flying along the inside of the exhaust pipe causes air friction. which slows down the air. slowing down the air causes more backpressure. also.... the faster something moves the more the ratio of air resistance is increased. which is why it is that much harder to go 10mph faster from 180 to 190 then it is to go from 30 to 40. the bigger the pipe the more room there is for the air and the slower air has to move and the less effort it takes to move that air. if u need to see the proof in the air friction along the walls of the pipe try blowing through a straw. then cut the straw down to 1/4 the size then try blowing through... youll feel alot less resistance. even though the smallest diameter hasnt changed. and to the person that said air expands as it cools.... uve apperently taken nothing remotely close to physics. water is the only compound in the world that expands when it gets colder. why u ask. as water cools down its ability to carry oxygen increases. and since there is more oxygen in the water theres more matter. its easiest explained as having micro bubbles in the ice.

i donno what credentials these other people have for making their arguement but i had a yearly average of a 99.3 in physics. :rolleyes:

[doug]

You brought this two year old thread back, and didn't even bother to read it? :rolleyes:

So I guess in your analogy a 12" exhaust is better than a 10" exhaust. What some people were trying to point out is that there comes a point where big enough is big enough, especially with small to medium size turbos.

water is the only compound in the world that expands when it gets colder.
Wrong. Rubber does that too.

[revmatch]

This is a 3" exhaust debate in advanced tech. :(

[Asmodeus]

Velocity also plays a role. With a properly tuned exhaust system alot can be accomplished. Meaning, each exhaust pulse will in fact create a vaccum that pulls the next in its wake. If you put a 8" exhaust on the pulses will lose their velocity which will nullify any chance of them pulling the next. Air friction would also reduce velocity but so would piping thats TOO large. Thus, flow bench, dyno, and R&D.

Your points of shortening the length of the tube are irrelevant as that is not what we are doing. The idea is to increase efficiency by getting a thicker straw. And still, you're not breathing fiery air in pulses... :rolleyes:
So...

[Cranked PSI]

3" flow a lot more air. Period. However, you need a good waste gate or you'll have boost creep with the smaller turbos. Put it this way. If you want an 11 sec or faster car, get a 3". I'm not an engineer, but read Buschur's site and he lays it out pretty well.

[need4speedTSI]

Why is this always discussed? 2.5 will get you into the high 11's in decent shape. You can go 3" but unless your pushin over 400 hp I say 2.5 will get you there, over 400 go 3". You can go 3" with less, have fun with boost creep unless your external. Lay this to bed already :confused:

[talontsi222]

"Isn't a 3 inch exhaust overkill" Heck no fooo, you will have much better top end..

[jepherz]

You have it backwards 99gst. Think about it this way, in terms of water. In the gas state, it requires more space, less space in liquid and even less in ice.

As the exhaust moves futher from the engine it cools and comes more dense(needing less space), closer to the engine the hotter it is and expands more(needing more space). So have bigger piping closer to the engine.

This sound right to all you guys?

Last time I checked, GAS was compressable. Therefore, there is no "space" that it is taking up. Also, when water turns to ice, it EXPANDS, hence why shit blows up when it freezes.

Besides the fact that hotter gasses are less dense and therefore flow through a smaller pipe easier, think of an exhaust like a wire. Since your whole exhaust (or wire) is acting as resistance, the more distance the gases (or current) travel, the more back pressure (or voltage) occurs (is lost).

Basically, the pressure drop occurs on the walls of the piping, so the longer you have a small diameter pipe in comparison to a larger one, the more back pressure.

I think this topic has been beaten to death almost as many times as the 6-bolt vs. 7-bolt topic. In our cars, all the backpressure needed is given by the turbo. Therefore, the less restriction post-turbo, the better.

[wheelhop]

Velocity also plays a role. With a properly tuned exhaust system alot can be accomplished. Meaning, each exhaust pulse will in fact create a vaccum that pulls the next in its wake. If you put a 8" exhaust on the pulses will lose their velocity which will nullify any chance of them pulling the next. Air friction would also reduce velocity but so would piping thats TOO large. Thus, flow bench, dyno, and R&D.

Great description of how an N/A exhaust should be designed. . . But we're talking turbo here. There is little to no vacuum pockets in an exhaust pipe after the turbine wheel. The turbine blades chop up the pulses to almost pure constant flow... Larger does so much better. The best is a "horn" shape. Expanding exponentially from the turbo to the exhaust tip.

Nevertheless, the turbine functions on differentials. As the volume in the hotside decreases (the exhaust stroke), the pressure goes up (PV=nRT). Also, as the temperature inside the hotside and cylinder is significantly higher than the ambient temps, there is an increase in pressure over the turbine blades ("heat expansion"). The best way to "show" a turbo these differentials is by opening the exhaust. The turbo can "see" the temperature outside better. It can better "see" the lower atmospheric pressure.

Lower velocity in the ideal way to "show" the turbo that there is a lower temperature (velocity of the individual particles).

Your points of shortening the length of the tube are irrelevant as that is not what we are doing. The idea is to increase efficiency by getting a thicker straw. And still, you're not breathing fiery air in pulses... :rolleyes:
So...
Regardless, a shorter exhaust works best w/ a turbo as this brings the lowest different temperature and pressure closer to the turbine wheel. This causes more work to be done to the turbine wheel over unit time (energy). The closer the different pressure and temperature, the more quickly it spools.

[Turbocharged]

Wow, one of these threads again... and just as much misinformation as usual. Stop making assumptions on fluid/thermo dynamics when you are not educated on the subject.

Try running 2.5", 3" and 3.5" exhaust. Then try running without a downpipe. Did you notice a difference in performance. Yes, you sure did. The less resistance to exhaust you have the faster your turbocharged car got. I have been there and done that.