[Hib Halverson]

To get 500 SAE at the flywheel w. stock manifolds and cats you need:

Ported heads
Ported housings
Fully or partually ported plenum
Cams reset
Bigger injectors
Low restruction air filter assembly
Exhaust manifolds deburred internally with port entries blended.
Stock cats with cat entries deburred and blended.
Low restriction exhaust system w. 2.75" or 3.0" pipe
Aluminum flywheel
93-94.5 octane fuel
Proper calibration

With the above set-up, my engine made 416 SAE at the wheels on a DynoJet and, using the .82 correction for C4 manuals, 507 SAE at the flywheel. The exact power output depends on the dyno and a host of other issues unrelated to the engine itself. Many other engines with similar packages of mods have made 495-505-hp SAE at the flywheel.

If headers are legal in your state, given proper cal and exhaust system, their addition will get you to 510-520 SAE at the flywheel.