cannot make over 10 psi of boost

[projectile]

Check your exhaust pressure before the turbo. Might be an easy way to find a serious problem(Wrong turbine wheel for your housing, damaged wheel,open or defective wastegate,...)

Do you have an easy way to check exhaust backpressure before the turbo (o2 sensor bung or something)?

I can't think of anything else (at the moment) that sacarguy didn't mention or that you haven't tried.

[camcojb]

Originally Posted by projectile

Check your exhaust pressure before the turbo. Might be an easy way to find a serious problem(Wrong turbine wheel for your housing, damaged wheel,open or defective wastegate,...)

Do you have an easy way to check exhaust backpressure before the turbo (o2 sensor bung or something)?

I can't think of anything else (at the moment) that sacarguy didn't mention or that you haven't tried.

no, there's nothing to hook into between the engine and the turbo; you don't want an O2 on the pressure side, so the bungs are in the downpipes.

Jody

[deuce_454]

your headers look VERY blue, my guess, (which is only a guess) is that the turbos are on the small side, you could be at the surge limit at 10 pounds, have you done the math and checked the turbo maps?? it could be that the housings are the limiting factor.

you could be moving the same mass of air at 10 pounds thru the bigger heads as you weer at 15 pounds with the old ones.. and its the mass, not the pressure that matters, the ET 245 heads flow like a MoFo and on a 402 with your super optimal intake and hot side tubing, you could be outflowing the turbos

[camcojb]

Originally Posted by deuce_454

your headers look VERY blue, my guess, (which is only a guess) is that the turbos are on the small side, you could be at the surge limit at 10 pounds, have you done the math and checked the turbo maps?? it could be that the housings are the limiting factor.

you could be moving the same mass of air at 10 pounds thru the bigger heads as you weer at 15 pounds with the old ones.. and its the mass, not the pressure that matters, the ET 245 heads flow like a MoFo and on a 402 with your super optimal intake and hot side tubing, you could be outflowing the turbos

The turbos were spec'd by Precision for my combo. They are T67's that flow like T76's according to Precision, and have the larger .81 exhaust vs the more normal .68 exhaust housing. They claim they are plenty big enough for 1400 hp. I actually was thinking they were on the big side as I didn't want a laggy engine, but they're not laggy at all, come up on boost nicely. They just don't make as much boost as they should.

As a comparison, I had this engine in my GTO with a pair of GT3072R turbos that made 16 psi no problem, could have made more but that was as high as I ran them. They were much smaller turbos than what I have now.

I'm going to hook a boost gauge to the outlet of one of the turbos first to see what the boost pressure is before the intercooler, just to eliminate that as an issue. If that's near 10 psi then I'm going to shim the wastegates closed so they cannot physically open and see what happens.

Jody

[Ketzer]

Stones of steel. I'd be terrified to block off the wastegates and try to force up the boost. I know you guys are all really knowledgable and this is easy peasy for you, but with the coin you've got invested, I'd be sweatin' bullets watching the boost gauge on that test run.


Jeff-

[camcojb]

Originally Posted by Ketzer

Stones of steel. I'd be terrified to block off the wastegates and try to force up the boost. I know you guys are all really knowledgable and this is easy peasy for you, but with the coin you've got invested, I'd be sweatin' bullets watching the boost gauge on that test run.


Jeff-

I think I could modulate it with my right foot pretty easy. I don't plan on going wot for a 1/4 mile pass, just load the engine and see if the boost swings past 10 psi. Going to check the boost on the inlet side of the intercooler now before any other changes, will post back on my findings.

Jody

[ohcbird]

"Hits a wall at 10psi"

Since you've eliminated all the other variables, I'd check the exhaust pressure going into your hot sides. If you're seeing over 20 PSI there (2:1), then you've found a restriction. The closer to a 1:1 ratio, the better. As a side note- do you have any EGT probes? I'm curious as to what your gas temps are hitting. Do you notice a more-than-normal rise in IAT when you're on the boost for a while?

I agree that your .81 housings are about right & should work fine, but you might be right at their limits already. I think that motor is trying to move alot more air than it currently can, hence the 'wall' effect. I think you can get 1.01 housings for those; that might be worth a try.

[deuce_454]

Originally Posted by ohcbird

"Hits a wall at 10psi"

Since you've eliminated all the other variables, I'd check the exhaust pressure going into your hot sides. If you're seeing over 20 PSI there (2:1), then you've found a restriction. The closer to a 1:1 ratio, the better. As a side note- do you have any EGT probes? I'm curious as to what your gas temps are hitting. Do you notice a more-than-normal rise in IAT when you're on the boost for a while?

I agree that your .81 housings are about right & should work fine, but you might be right at their limits already. I think that motor is trying to move alot more air than it currently can, hence the 'wall' effect. I think you can get 1.01 housings for those; that might be worth a try.

my thought exactly.. but check the boost before at the turbines just to be sure....

you could have another issue causing it.. some manual boost controllers need to be plumbed to both sides of the diagphram on the wastegates.. so they hold them closed by applying pressure on top to hold the valve closed till the boost hits preset, and then they release this pressure to allow the valve to open.... just make sure you havent got the hoses crossed (mounted wrong) on one or both sides so your boost controller is actually opening the valve instead of keeping it closed

[sacarguy]

Originally Posted by deuce_454

your headers look VERY blue, my guess, (which is only a guess) is that the turbos are on the small side, you could be at the surge limit at 10 pounds, have you done the math and checked the turbo maps?? it could be that the housings are the limiting factor.

you could be moving the same mass of air at 10 pounds thru the bigger heads as you weer at 15 pounds with the old ones.. and its the mass, not the pressure that matters, the ET 245 heads flow like a MoFo and on a 402 with your super optimal intake and hot side tubing, you could be outflowing the turbos

not even close those t-67 can support over 700 horsepower each no way they cant supply more then 10 psi to that motor he would be having to make 1000 rwhp at 10 psi to out flow those turbos.

did you change the cam shaft profile to much over lap can easily cause such a issue

[camcojb]

well, I found the reason I'm having a problem with the boost levels. The intercooler was not built for this power level, and simply won't support my airflow needs.

I have a 24" wide by 12" tall and 3" thick core with side tanks. So the unit has air flowing horizontally, which is very restrictive with that config of a core. If I could swap to a vertical unit, the same size core would be much more efficient as it'd be 24" wide and only 12" long. Unfortunately that won't fit without a complete re-doing of the front end of the car. According to Bell my intercooler config and size is only real efficient up to 400 hp or so.............

The tech at Bell guessed the exact boost drop of my combo just off the intercooler specs and boost level into the core; I didn't have to tell him. My plan is to bypass the intercooler for now and plumb the turbos directly into the throttle body and run water injection as I have in the past. It may not be ideal but it definitely works and I'm sure the power difference will be huge.

Thanks for all the help, it is much appreciated.

Jody