What's the limit on this setup?

G

GNDriven

Active Member
Joined
Dec 9, 2004
Stage II 274" GN1 heads/intake maxed out / DLS cam. Th400/PTC converter. Stock ignition now, but changing to a MSD Power Grid soon. RJC big air/air. 120lb injectors / race gas. Turbo is a Comp with Pro-mod compressor cover 76mm billet / Turbine = 79mm with a undivided 0.96 AR (I think) maybe one step larger.Car is 3500lbs with driver.

Currently I have been 146.6 on 26.6 lbs. Shifting at 6500/ traps at around 6200. The car is responding 1 mph/1 psi increase on boost. I am wondering where is my ceiling and what is going to be the limiting factor. Is it going to be back pressure (which im not logging yet). I would like to max out this turbo compressor capability if I can. I'm watching the TSL guys and wondering what power limitations (wall) do they hit first.

Thanks.
 
GNDriven said:
Stage II 274" GN1 heads/intake maxed out / DLS cam. Th400/PTC converter. Stock ignition now, but changing to a MSD Power Grid soon. RJC big air/air. 120lb injectors / race gas. Turbo is a Comp with Pro-mod compressor cover 76mm billet / Turbine = 79mm with a undivided 0.96 AR (I think) maybe one step larger.Car is 3500lbs with driver.

Currently I have been 146.6 on 26.6 lbs. Shifting at 6500/ traps at around 6200. The car is responding 1 mph/1 psi increase on boost. I am wondering where is my ceiling and what is going to be the limiting factor. Is it going to be back pressure (which im not logging yet). I would like to max out this turbo compressor capability if I can. I'm watching the TSL guys and wondering what power limitations (wall) do they hit first.

Thanks.
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TSL is backpressure limited by the turbine. Traps in the high 150's. The cam grind/cam timing/CR, air quality will determine the power potential.
 
Its not a big cam for the application. Do you see any reason why this combo will quit making good gains 1psi increase = 1 mph say up to about 155?
I am wondering if I am going to start getting into the 1.25psi per 1 mph real soon.
 
GNDriven said:
Its not a big cam for the application. Do you see any reason why this combo will quit making good gains 1psi increase = 1 mph say up to about 155?
I am wondering if I am going to start getting into the 1.25psi per 1 mph real soon.
Click to expand...
it will take more power to mph. The car has to punch a hole through the air. If you were measuring the backpressure and compressor speed you can start seeing where it's tapering off. Don't confuse fast cars with big cams. They have to be big in the correct area not just big. More duration at .200 and ramping in from .050 up fast. The most efficient setups use less duration at low lifts. There is power in the cam when backpressre is rising fast. Most of the TSL type engines ive seen laid down between 33 and 35psi. If it's not making the power by then it's probably not going to.
 
Well I do have some low 15xs hopes and woukld like to run some TSL events this year. I have a larger divided (1.32) exhaust housing I can go up to. Do you think there is any additional flow through the turbine wheel going to the bigger housing?
 
GNDriven said:
Well I do have some low 15xs hopes and woukld like to run some TSL events this year. I have a larger divided (1.32) exhaust housing I can go up to. Do you think there is any additional flow through the turbine wheel going to the bigger housing?
Click to expand...

I can't recall the a/r I saw on the top running cars. Going larger doesn't guarantee power but I'd try it for sure. You really need to log backpressure, manifold pressure, and shaft speed and watch the ratio of intake pressure to ex. If you see shaft speed increasing and backpressure rising but manifold pressure isn't gaining at the same rate it's running out of steam.
 
So when I observe the above mentioned, do you mean that is where the turbo compressor is running out of steam or when the turbine is limiting the airflow through the engine (backpressure)?
If it is where the turbo is running out of steam, that is what I am looking for right? I will be using all the available air mass from the turbo compressor.
Or at that point of backpressure rising, could you make an exhaust change to increase exhaust flow at which point the intake manifold pressure will start rising again?
 
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