You are majorly effecting power squeezing it down to 4" on the intake. It will spool quicker and run alot harder when that is fixed. Also the rubber adapter on the front of the charger will suck it self closed furter restricting flow. That will need to be updated when the engine comes down.Other then that is looks nice.
If you need help let me know...
Dan
I agree that necking down to 4" is not the greatest, but I highly doubt that rubber will suck itself closed - it is the same stuff that SuperDiesel and I used to make our intakes, you could probably stand on it without it flattening all the way.
I have a 5.5" inlet on my S475's race cover, I used a 5.5" to 6" elbow on the turbo with 6" intake piping.