Thats the great thing about this setup even if you are restricted by the small turbos exhaust housing it doesn't really matter. I think Im only going to be running the small turbo somewhere around 17psi which is well under what it can handle. You got to think, the larg turbo is for low pressure, your supplying your smaller turbo (high pressure) with already compressed air where it will then be compressed again and blown into the motor. This is why you can run much higher boost levels. I think we only have to run the large turbo at around 11psi to supply the small turbo with enough pressure to compress it to the pressure we need to make 500hp. I say "I think" because i am not the expert on this stuff. I understand the concept and all but as far as the math goes, thats all my mechanics job. There are a couple of faq sites about compound turbos. They have really good info that is pretty easy to understand until it gets into the math portion of it all. Take a look, they will be able to explain alot better than i can.