Hate to say it but JW is right. Less backpressure is better on a turbo car unless you go too big. Spool is better too because the air can move faster with the larger exhaust.

 

cut-out

He's right, Less is better! Have you heard of a cut-out?
The old muscle cars have them to open the headers up for more flow, I have one...I love it! Sounds cooler than shit and you can hear the turbo spooling at idle! 3 wing nuts and it open....
kid

 

Damnit. I should still be a new dsmtalker.

Ahhhh. Oh well, at least my question is answered.

BTW, What is a cut out?
Is that like a test pipe minus the test pipe?

 

I have/had a test pipe with a custom cut out welded onto it. the thing was awsome, 3 bolts and you had a nasty sounding exhaust. i am looking to get rid of it. email me

 

I always hearf of "Cut-Out's" referred to as dumps myself. Either way, I can't even imagine what it would sound like on a 4 Cylinder.

Turbo spooling at idle... that'd be bad ass!

 

mmmm

Less back pressure equals quicker spoolup.
The higher the pressure differential between the inlet of the exhaust housing and oulet the quicker the wheel will spool up as the high pressure gas wants to go low Pres. as soon as possible.
Thats why turbos are scroll shaped.

 

good reading

Turbo Fundamentals

 

I've heard of these cut outs, does anyone have a pic? Yeah, the exhaust turbine provides all the needed backpressure in a turbo car so there is no need to allow the exhaust to provide any.

 

I thought you've been into DSM's for 4 years talon318, shouldn't you know that turbo's need less backpressure to spool? The less backpressure the faster the spooling. With just a straightpipe (cat is restrictive therefore creates a lot of backpressure) w/ 3" catback my T-25 spools instantly even from low RPMs. A 2.5" downpipe w/ 3" catback setup will give you more torque on the lowend while sacrificing topend. But if you're running a mutt then you should go for full 3", and port the O2 housing to eliminate creep.

 

Damn Blitz!

I thought we got over this childish bashing. Oh well, guess some kids never learn.

Thanks for the info BadDSM.

Looks like I have another web page to add to my favs.

Originally, what JW said I used to think.
Until some smart turbo guy said otherwise.

I guess I listened to a moron and have believed him ever
since. Thats ok, my full exhuast is:

HRC 3in o2 eliminator dp
3in test pipe or cat
3in Apexi Dunk

Peace.

 

The whole conversation started when I told him I've got this in the mail:
http://store.summitracing.com/partdetail.asp?part=830

 

Just out of curiosity JW, where did you install that hog? I think adding something like that instead of a race pipe would be a sweet idea. Forget bolting up the race-pipe at the track... Open up the DUMP!

P.S. Any chance you can describe the sound? Better yet, anybody with one of these have a WAV file by any chance?

 

Just out of curiosity JW, where did you install that hog? I think adding something like that instead of a race pipe would be a sweet idea. Forget bolting up the race-pipe at the track... Open up the DUMP!

P.S. Any chance you can describe the sound? Better yet, anybody with one of these have a WAV file by any chance?

The part is still in the mail. So, no sound yet
I am too lazy to type, this is the email i sent him. Take it for what it's worth:

I want the Y-pipe to go before the cat so the lower
pressure from the dump will suppose give something
similar to a open DP effect. It will not flow as good
as a open DP but close since gas prefer to flow from
high pressure to low pressure. Some will still pass
through the cat because of the force/momentum of the
exhaust flow. We will see.

 

I always hearf of "Cut-Out's" referred to as dumps myself. Either way, I can't even imagine what it would sound like on a 4 Cylinder.

Turbo spooling at idle... that'd be bad ass!

I've got a 3" cut out on my 97 GSX and it sounds like a dumptruck!

 

Cut-Out

I have mine where the cat used to be, After flex section....
My friends call me Turbo Tractor...Its cool, because when you rev it up, you can hear the turbo spool and the down spool sounds even better...I wish I had a wav. file....Every one would go out and get one!
kid

 

Re: mmmm

Less back pressure equals quicker spoolup.
The higher the pressure differential between the inlet of the exhaust housing and oulet the quicker the wheel will spool up as the high pressure gas wants to go low Pres. as soon as possible.

That's it in a nutshell! The pressure differential is key.

I'll still stay with my 2.5" dp, 2.5" tp, and 3" cat-back though. From what I've seen/read so far, my mf1 l3 spools faster than anybody elses... I'm sure it'll take me where I want to go, hehe.

 

I really hate to ask this, but this thread got me thinking and after seeing Van's post, I'm a little curious. I know how a FULL 3" turbo back may sacrifice your low end (torque?) a bit, but will help in the topend and a 2.5" DP to a 3" Cat-Back will do the opposite. My question is to what extent is the differences? Now, the part I don't really want to ask... If Van is running a Mutt L3, and has no complaints, it makes me wonder when this whole scenario actually takes effect. To my understanding, that's a pretty large turbo, and flows a great amount of air. Is a 3" DP vs. 2.5" DP gonna help the car dramatically around top end, and if so, anybody got a ball park figure of what RPM and above? As of now, I plan on getting the T-28 from FP and with all the talk in this thread, I personally would see a 3" DP not fitting the situation as well as a 2.5" for that particular application.

Thanks for any clarification

 

hmmmm....

After looking at all these different combos...

But what about a 3" dp and 2.5 cat-back... I would think some of that backpressure isn't lost. Maybe slightly faster spool? Well, since I have a 3" dp (not installed yet) but I still have my (fairly new but installed) Greddy 2.5" exhaust. Would a setup like this cause some kind of bottleneck/restriction once the flow reached the cat-back? Would something like this be ok? I'm fairly new, so please don't flame me for the newbie question Thanks,

James

 

3" to 2.5" should naturally have some kind of a bottleneck effect but if you're not running a really big turbo then I doubt you'd notice the restriction too much. I pretty much had the same setup, EVO 3 O2 housing, 3" DP, 2.5" press bent piping, 3" muffler. That setup was good enough for 104mph traps for me but I'm sure some went faster w/ just a 2.5" exhaust.

 

i have a 3" dp to a 2.5" borla exhaust. in my own measured 1/4 mile i trapped at ~110. i think it will take me a lot lower as soon as i get my injectors installed and my safc so i can tune becuase i am running pig rich right now.

 

exhaustcutouts.com sells a cutout with a cable that you run to the cockpit.

Imagine.... revving on someone... vrrmmm, vrmmmm.... the flag drops... pull the lever to open the cutout... VWAAHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHshiftBWAHHHHHHHHHHHHHHHHHHHHHHHHHHH

lol

and if cops come, shut the cutout! they'll never know it was you!

Exhaustcutouts.com is being lame and not working right now, just search for 'exhaust cutout' on ebay... they're around $40. universal fit.

 

i have a spare one hanging around if anyone wants it PM me, ill let it go cheap.
-Greg

 

You will probably get more low end power from a 3" exhaust than a 2.5". The turbo will spool faster because of less backpressure. I don't see any reason why you would want the DP bigger than the cat back. The catback takes all the exhaust, the DP just routes the extra exhaust the turbo doesn't need around it so you don't have boost creep. You will only see a gain in the top end with a bigger DP.

 

jcwhitney sells cutouts for $22 (the kind you can open/close from the cockpit).

 

How exciting are cutouts!!!!! I am ordering one today. Some questions though. I have a obx muffler but the rest is stock. What would be the big gain of opening up your exhaust before the muffler. Remember i am stock except for muffler.