If you look at plenty of Turbo intercooled 4.0L Falcons in Street Fords and on here, a pretty common power output is apparent. It works out to be ~10rwkW per PSI boost. This is for stock compression, stock cam and stock AU heads.

Consider that a NA engine has 14.7PSI of atmospheric boost and the engine is 135-150rwkW with intake & exhaust modsas well as tuning.

The guys running 8psi boost (ie 22.7psi) seem to be around the 230rwkW. 10psi oftens sees 250rwkW.

Mike's dyno EA which has run a 9.98s quarter mile runs 21PSI and has 350rwkW. He has ported head etc, but the drivetrain (3spd auto) would be chewing up some of the engine power.

The ones which are chasing more than 300rwkW seem to be guys with lowered compression. Such as the above.

If you run intercooling, that can go a long way towards being able to run higher boost and still keeping stock compression, a decent air-fuel/lambda and reasonable engine timing which is a big factor in making power.

Save the rebuild money for good tuning!

Thats a great explination mate thankyou, its a good reference for turbo apps, psi-rwkw.