450rwhp on 6lb boost with custom STS turbo setup on LS1. Best mpg on stock cam 32.7 imperial (28mpg US); since cam upgrade down to 31mpg best (26.6mpg US). Fitting turbo made no change after cam except when driven in anger. Runs water/meth injection on boost at 50/50 mix. Worth 45rwhp.
4 into 1 headers with 1.75" primaries into 3" merge collectors. 2 x 3" high flow cats. All merged into a single 3" exhaust to rear mounted turbo with smooth bends and quality welds all in stainless. Smooth aluminum intake pipe from turbo in rear to engine, starting at compressor outlet size and running straight as possible 2.5" under car then setting up to 3" then 4" just before throttle body. 051 slightly tighter head gaskets to tighten quench and aid compression. 20 hours of dyno time to get tune as good as possible. Lean burn.
Rhoads roller lifters to drop cam duration at lower rpms and allow engine to run leaner cruise mix plus use less fuel at light loads.
Plasma ignition being considered to get even leaner and maintain hp.