I am running an 83mm GSR motor w/ 9:1 compression, a JG manifold , custom turbo manifold(similiar to ram-horn), and a 60-1(stage 3 .82 a/r... .70 a/r compressor).

Here's the prob:
I dyno'd with this turbo and an ss autochrome manifold, stock intake manifold and tiny intercooler. it was 405 whp and 330 tq(18 psi). The problem was that my power amd torque peaked early(below 7k) and fell off to redline. We thought this was due to lack of exhaust flow to spool the turbo at high rpm's.

After adding all the current parts and dialing the air fuel and ignition timing in, the power output was slightly down and the power and torque curves were about the same...

What's going on? Is it for sure the turbo i am running or could it be something else?