I have RT high flow cats on my Z. Is this going to affect my PSI as well. I bouth them from Stillen so I thought it would not hurt power gains. What are you going to change to?

 

You will loose a little boost with HF cats. I have not proven this but I don't believe you loose any power. You are making your engine more efficient which may not gain you power but I also don't think you loose any. If I could make the same amount of power with headers and HF cats @ 2psi less boost I would do it because it is easier on your engine.