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Discussion Starter · #1 ·
Ok I made a new personal best in the 1/4 mile. (12.05 @ 117.7 MPH) I'm really happy with it but I did noticed that I have boost drop off at higher RPMs. I start at 24-25psi and by redline it drops to 21-22psi.
2 weeks ago I figured out I had lots of small boost leaks (vacuum hoses) and fixed them all. All is well but yet I still have drop off. Now on my logs I see that it is raising lbs/min but my guage says its dropping psi pressure. The max lbs/min to make my new 1/4 mile best was 37.74lbs/min.

Other than that, my car is golden, no problems, no knock at all, just a steady rise in timing with no flatline.

What could it be?
 

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Your turbo is out-flowing your motor..
 

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stillbroke said:
Your turbo is out-flowing your motor..
Exact opposite. Pressure is resistance of flow. If you have more resistance (ie your turbo producing more air than your motor can ingest) you will have a higher boost presssure. You are thinking of when a motor is very efficient at high rpms and the turbo can't keep up.

I suspect it isn't the turbos fault, if you are running that fp turbo, it should be able to keep up with the motor just fine. The way it is acting now is much like how a 16g acts.
 

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Discussion Starter · #6 · (Edited)
sleepwalkindsm said:
What are you using for boost control? Maybe try getting a stiffer spring in your Tial wg.
I have the 44mm Tial Wastegate with the stock spring. I did test to see if I had the wastegate blown open by running the car with no boost source on the wategate and it went up to 30 psi :eek: before I let off the gas. Boost controller is a Joe P MBC. The Pro Z

wishihadatalon said:
Exact opposite. Pressure is resistance of flow. If you have more resistance (ie your turbo producing more air than your motor can ingest) you will have a higher boost presssure. You are thinking of when a motor is very efficient at high rpms and the turbo can't keep up.

I suspect it isn't the turbos fault, if you are running that fp turbo, it should be able to keep up with the motor just fine. The way it is acting now is much like how a 16g acts.
Yep its acting like a 16G. So you think my engine is injesting more airflow than the turbo is able to produce pressure wise. That would mean raising the boost would be the solution :)D )

4g64fiero said:
Exhaust LEAK!!!!!!!!! blaaAAArrGhHHSAAHGZZZSSHAAARRGGTUNST!!!!!
With exhaust, I'm using the custom 3" FP Recirculated O2 and 3" piping to the Muffler. Test pipe was used for the runs. (No cat) The 3" Downpipe is attached via V-band. I highly doubt there is an exhaust leak. I will check over the exhaust Manifold bolts to see if they are loose although I also doubt this as I bought Brand new Factory studs and nuts. The Copper factory nuts are oval and self lock. All gaskets are factory and is brand new since I rebuilt the engine for this turbo.
 

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tarantula said:
Ok I made a new personal best in the 1/4 mile. (12.05 @ 117.7 MPH) I'm really happy with it but I did noticed that I have boost drop off at higher RPMs. I start at 24-25psi and by redline it drops to 21-22psi.
2 weeks ago I figured out I had lots of small boost leaks (vacuum hoses) and fixed them all. All is well but yet I still have drop off. Now on my logs I see that it is raising lbs/min but my guage says its dropping psi pressure. The max lbs/min to make my new 1/4 mile best was 37.74lbs/min.

Other than that, my car is golden, no problems, no knock at all, just a steady rise in timing with no flatline.

What could it be?

Just to add, just because boost falls, doesnt mean HP is.
Boost itself is not equal, or measureable to air flow. But I will agree that your turbo should be able to hold its boost thru redline under 25psi.
What rpm is the boost falling?

It does sound similar to 16g characteristics, and even similar to the evo3's airflow ( 37lbs/min)as my E316G setup hits 25psi and is always down to 21 around 7k as well.

Turning the boost up a few more lbs helped for me in getting a few more lbs at redline, but I couldnt continue running the psi that high nor do I think a 16g should be boosted that high and I am limited to 93octane unlike you; but you could turn it up a bit to give it a shot. Also doing a blow thru setup and CAI helped me some as well with boost drop off.

Do you have cams, sheet metal intake manifold, what displacement?
( Sorry I couldve just looked at your profile but im lazy)

All of that will be a factor in how fast you are digesting the air your turbo provides, the quicker your motor can flow the more work your turbo has to do to hold X amount of pressure at Y rpm.

Are you internally gated?
If so I would suspect your flapper is blowing open, or just plain out leaking from not closing all the way... An external gated setup with a stiffer w.g. spring would probably help to say the least.
 

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Discussion Starter · #9 ·
Black_ bullet said:
Just to add, just because boost falls, doesnt mean HP is.
Boost itself is not equal, or measureable to air flow. But I will agree that your turbo should be able to hold its boost thru redline under 25psi.
What rpm is the boost falling?

It does sound similar to 16g characteristics, and even similar to the evo3's airflow ( 37lbs/min)as my E316G setup hits 25psi and is always down to 21 around 7k as well.

Turning the boost up a few more lbs helped for me in getting a few more lbs at redline, but I couldnt continue running the psi that high nor do I think a 16g should be boosted that high and I am limited to 93octane unlike you; but you could turn it up a bit to give it a shot. Also doing a blow thru setup and CAI helped me some as well with boost drop off.

Do you have cams, sheet metal intake manifold, what displacement?
( Sorry I couldve just looked at your profile but im lazy)

All of that will be a factor in how fast you are digesting the air your turbo provides, the quicker your motor can flow the more work your turbo has to do to hold X amount of pressure at Y rpm.

Are you internally gated?
If so I would suspect your flapper is blowing open, or just plain out leaking from not closing all the way... An external gated setup with a stiffer w.g. spring would probably help to say the least.
I have a Tial 44mm External Wastegate. Its a FP total setup. It was shipped to me already put together. Never took it apart. I have stock cams/head/valves/intake manny and the stock 2.0 engine. (Stock Pistons ets)
The tial has the stock spring which is .9 Bar/13.053 psi Large Blue spring.
 

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tarantula said:
I have a Tial 44mm External Wastegate. Its a FP total setup. It was shipped to me already put together. Never took it apart. I have stock cams/head/valves/intake manny and the stock 2.0 engine. (Stock Pistons ets)
The tial has the stock spring which is .9 Bar/13.053 psi Large Blue spring.
Well you shot down all my ideas :dunno:

Sorry I didnt read were you had said you already had an external gate earlier. Try a stiffer spring combo in the wastegate perhaps?

And check again for boost leaks, and or exhaust leaks like others mentioned.
Also, make sure your intake pipe coming off the turbo is prperly sized with the diameter of the compressor inlet..
It may sound basic, but I just helped another memeber with similar boost issues because he was running a stock intake arm off of a larger turbo and it was choking him and not bringing in enough air. Sounds like your restricted somewhere in terms of air flow...
 

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wishihadatalon said:
Exact opposite. Pressure is resistance of flow. If you have more resistance (ie your turbo producing more air than your motor can ingest) you will have a higher boost presssure. You are thinking of when a motor is very efficient at high rpms and the turbo can't keep up.

I suspect it isn't the turbos fault, if you are running that fp turbo, it should be able to keep up with the motor just fine. The way it is acting now is much like how a 16g acts.
So what your saying is, he most likely still has a boost leak, or pre exhaust leak?? Because there's no reason why that fp turbo wouldn't be able to keep up with the motor, specially at 25psi "even with the stock cams/Itake mani etc..." I would think that turbo should hold 30+psi without problems, like his motor not being able to ingest the air quick enough, am I correct in assuming that?? I'm trying to makes sense of all this but I'm confusing myself.. lol..

To the op, congrats on your time and its seems like you'll have no problem breaking into the 11's when you get this figured out. Just to make sure, you did BLT off the turbo and off the t/b right?? Check those pre turbo exhaust leaks and then maybe even try a stiffer w/g spring..

Black_ bullet said:
Also, make sure your intake pipe coming off the turbo is prperly sized with the diameter of the compressor inlet..
It may sound basic, but I just helped another memeber with similar boost issues because he was running a stock intake arm off of a larger turbo and it was choking him and not bringing in enough air. Sounds like your restricted somewhere in terms of air flow...
+1, I didn't even think of that being a factor.
 

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Discussion Starter · #12 ·
Black_ bullet said:
And check again for boost leaks, and or exhaust leaks like others mentioned.
Also, make sure your intake pipe coming off the turbo is prperly sized with the diameter of the compressor inlet..
Like I said. Its all FP Including the 4" Intake.

When I did the BLT, I put it on the turbos compressor inlet. I bought a 4" pipe cap and also an extra 4" Silicone coupler. It bolts on to the turbo just like the 4" FP intake pipe.

I checked the EX manny and it doesn't seem to have any leaks. I will do another boost leak test. I also raised the MBC an 1/8th turn to see the results. The boost drop off is higher RPMs, 6K. I shift at 7K+
 

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After you double check from the turbo inlet I would do one at the throttle body elbow and check the intake mani, injector seals etc, from what I've experienced, this can be the harder area to blt, "you will obviously have to build another tester for that:rolleyes: .." Just to verify, you are building 25psi on your boost gauge when you do the tests??
 

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A 13psi spring should be capable of holding your desired pressure without an issue. To be safe I would pop the cap and verify the spring colour for starters but this wouldn't explain why your flowrate is rising while the pressure drops.

There is no way the stock cams are outflowing that turbo. Not a chance. Also with a compressor that size, your boost leaks would have to be substantial to show a drop in pressure.

When your flowrate is rising and your pressure is dropping it means one of two things; cams outflowing turbo or boost leaks. I'm curious as to what MAS you're using.
 

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turbolover said:
So what your saying is, he most likely still has a boost leak, or pre exhaust leak?? Because there's no reason why that fp turbo wouldn't be able to keep up with the motor, specially at 25psi "even with the stock cams/Itake mani etc..." I would think that turbo should hold 30+psi without problems, like his motor not being able to ingest the air quick enough, am I correct in assuming that?? I'm trying to makes sense of all this but I'm confusing myself.. lol..

To the op, congrats on your time and its seems like you'll have no problem breaking into the 11's when you get this figured out. Just to make sure, you did BLT off the turbo and off the t/b right?? Check those pre turbo exhaust leaks and then maybe even try a stiffer w/g spring..



+1, I didn't even think of that being a factor.
Pretty much. Stock cams and intake manifold will make it easier to hold more boost. They don't allow the VE that is required for the engine to ingest so much air that the 3052 couldn't keep up. I didn't see a stock cams and intake manifold comment, so if I missed it I am sorry.

Have you noticed a slower spool up speed?
 

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I know, he posted it up after your posts;)
I'm just trying to get a better understanding of what you were saying, that is all.
 

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90_talon_matt said:
A 13psi spring should be capable of holding your desired pressure without an issue. To be safe I would pop the cap and verify the spring colour for starters but this wouldn't explain why your flowrate is rising while the pressure drops.
+ 1 for try a stiffer spring. If you have 13 psi with no boost control, you should have a LARGE blue spring in there. Try to get SMALL blue spring to put in with it to raise your lowest boost point to 20psi. Then use your boost controller for 25 psi or whatever you desire. This would make a lot more spring pressure to hold your wastegate shut.
 

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Discussion Starter · #18 ·
snb357 said:
+ 1 for try a stiffer spring. If you have 13 psi with no boost control, you should have a LARGE blue spring in there. Try to get SMALL blue spring to put in with it to raise your lowest boost point to 20psi. Then use your boost controller for 25 psi or whatever you desire. This would make a lot more spring pressure to hold your wastegate shut.
The only thing is getting that wastegate off. Thats a real pita. As for my Maft, I have Stock Mass sensor.
I tried to raise the boost 1/4 turn and it did hold a bit better. But it spikes beyond 25psi. I am going to do a boost leak test again. I'm also going to zip tie every vacuum hose.
 

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Tial rates thier springs to hold twice that of the spring set pressure. I can't see the 13psi spring being the issue and as I said above if your wastegate was opening your flowrate wouldn't be rising as your pressure tapered off, it would be dropping off at a similar rate.

It makes so much more sense for it to be a boost leak, especially using a 2g MAS. Your MAS and turbo don't know or give a shit about the fact that you're leaking pressure so as they keep pumping and metering away happily your pressure is tappering off and you flowrate is rising innacurately.
 

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90_talon_matt said:
Tial rates thier springs to hold twice that of the spring set pressure. I can't see the 13psi spring being the issue and as I said above if your wastegate was opening your flowrate wouldn't be rising as your pressure tapered off, it would be dropping off at a similar rate.

It makes so much more sense for it to be a boost leak, especially using a 2g MAS. Your MAS and turbo don't know or give a shit about the fact that you're leaking pressure so as they keep pumping and metering away happily your pressure is tappering off and you flowrate is rising innacurately.
It could be a wg issue. I would actually recommend setting up the tial WG the way they recommend which involves both ports. http://www.tialmedia.com/documents/w3_tial_wginstall.pdf

You put your boost controller to the top port. You close the boost controller all of the way to restrict any boost signal from getting to the top part of the hat and pushing down on the valve. That is spring pressure. The way you up boost is to let air past the boost controller and for every psi that you apply on the hat, it will require an extra psi to inflate the diaphragm to open the valve. This is the correct way to regulate boost according to Tial instead of using just the side port.
 
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