I have a 88mm t6 1.39 are with a 111 turbine on my bbc and I was wondering what kind of problems would a turbo that is to small cause.I know the backpressure could be high but what are the actual problems or what do you look for to make sure your not hurting things.The turbo is on a roughly 600hp bbc before boost and will try to get around 8-10psi.Just wanting to keep a look out for problems and or ways to check for problems

 

Are you able to data log pressures or watch them? You can put a sensor before the turbine to check this pressure. You normally want 1:1 but up to 2:1 will let you know you have a problem.

 

I have ancient setup.Its a carb setup using a msd6 digital.So can I put a boost gauge fitting right before the t6flange and see what the pressure is there compared to my boost pressure under load.IF I can do something like this what is the danger of getting past 2 to 1 will the car be lean because I can watch my lm2 for a lean condtion..Just trying to understand the high iat condtion..thanks for the reply

 

As back pressure ratio goes up, it tries to force the intake charge back out of the combustion chamber because back pressure is so much higher than boost. Problems are that it can become more detonation sensitive, and as the ratio goes up hp/lb of boost will drop dramatically. You'll need extra fuel to help fight detonation. Most will say a 2:1 ratio is acceptable, but something closer to 1:1 will be easier on parts, and make more hp.

 

If you an dyno it, the graph shows you whats going on pretty easily as well. When you start to max the turbine peak torque goes up a lot and then torque and power drop off in the upper rpm quite drasticly.