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hey guys, finally getting some full power runs in our new car. running a 540, on gasoline with a PT2000 IC, using GT4788's with a .96 AR hot side.... and a few issues came up, well i guess maby they aren't issues but thats why I'm here asking.. we had the intake off and the runners are dirty and black about 1.5" up the runner.. and when making 32psi of boost i was logging about 46psi of back pressure... is my intercooler to small. or am i just making too much back pressure and the result is less boost?... i assume i should be in the search for some 1.08ARs for the turbos but I'm up for suggestions! thanks in advance Jake.
 

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hey guys, finally getting some full power runs in our new car. running a 540, on gasoline with a PT2000 IC, using GT4788's with a .96 AR hot side.... and a few issues came up, well i guess maby they aren't issues but thats why I'm here asking.. we had the intake off and the runners are dirty and black about 1.5" up the runner.. and when making 32psi of boost i was logging about 46psi of back pressure... is my intercooler to small. or am i just making too much back pressure and the result is less boost?... i assume i should be in the search for some 1.08ARs for the turbos but I'm up for suggestions! thanks in advance Jake.
increasing the turbine AR is likely to help drop backpressure somewhat, and lowering turbine backpressure can be worth HP, it is not uncommon for some reversion to take place in any engine, even stock ones. the PTC2000 might be a bit small for your application, but I doubt its a big handicap where your at now. Would a pt 3000 help, its likely.

as to your backpressure readings, our reading turbine pressure of 46psi at 32psi of boost ?

are you loging the pressure before and after the intercooler as well as tempature before and after, that would tell you how effective your intercooler is
 

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Discussion Starter #4
nope its a BS3 efi... and I'm measuring back pressure right at the T4 flange for the turbine... I'm only monitoring intake air temp, and at this time i don't have a psi sensor reading pressure drop on either side of the cooler. so essentially I'm reading 46psi in the headers and 32 going into the motor, is this acceptable? or am i supposed to be closer to a 1:1 ratio
 

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I dont think you have a bad back pressure ratio.
black soot 1.5" up into the intake runner sounds like a cam installed 1 tooth advanced
 

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If you want to correct the back pressure it will take a much bigger jump in A/R than what was posted above. What size turbine wheels?? I am running twin 80/96 turbos with 1.32 housings on a 402cuin sbc and have no issues spooling them and they are still about 1:1 on boost to drive pressure.
 

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92mm Turbines on a 540 inch motor is borderline too small...

Id be looking at upgrading the turbos to a GT50/52/55 turbine wheel instead of swapping turbine housings.
 

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92mm Turbines on a 540 inch motor is borderline too small...

Id be looking at upgrading the turbos to a GT50/52/55 turbine wheel instead of swapping turbine housings.
This...

I was about to say running 32 psi on a healthy 540 that revs to any decent racing engine rpm i would be looking at t6 flanged turbines with bigger wheels.

Do you have any idea what kind of power you are making?

I mean my 511 FE motor that's really not a "full race effort" engine would be making about 2200hp @ 32 psi (using engine modeling software so it may not make those numbers but it should flow that much air)... on a full race effort engine you could be past maxing the turbines and nearly maxing if not actually maxing the compressors.

these turbos are *only* good for 1400hpish each and that's with the bigger turbine in a single turbo configuration that they aren't pushing against each other. So if you are making 2500-2700hp ish you're giving her all she's got captain.
 

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A housing change will not help much at full boost.
You need a larger Turbine wheel. Getting a larger turbine wheel and staying T4 leaves you few options.
 
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