I have a completly stock 4.6 block and wanna put the kenne bell 500 hp kit, or maby the whipple 500 hp kit. I already have jba shorty headers and bassani cat back. From researching ive herd that might be a bad idea
you should be ok, many have the 500hp kit, thats what i got, and do well, as long as its tuned safely. and the 500hp is crank, so w/ a good tune you should wind up in the neighborhood of 450rwhp and safe a/f ratio.
i had 470 at the tire for 2 years and drove the car like I stole it. I never worried about the engine in my car because it is all in the tune. There have been guys making 550 at the wheels and they lasted for a while. Y ou can blow the motor with 5 psi. with a crappy tune but you can also drive it with 550 rwhp with a good tune and it will last.
the rev limiter is the key, have it set high enough where you don't run into it because the computer cuts the fuel injectors off and that is when you blow motors up. I never rev my car above 6K rpm at any time. I have seen people making power up to 6500 rpm but you really don't need to go that high on a twinscrew supercharger because it makes power from idle to 6k but on a turbo or centrifugal supercharger then you want that rpm because that is where the car makes power at with those.
Get a good tune and watch the traction control and RPM's and the car should live for a long time
"Weak Won't Survive
Anyone modifying an '05 GT for more performance should be aware of the engine's limits. After all, it's not Ford's responsibility to provide an engine for racing, so consequently, the three-valve 4.6 was designed for 300 hp, plus a stress safety margin. Steeda says the engine will live with 425 hp as long as timing and fuel is managed to prevent detonation. Anything more than 425 hp and "You're just waiting to buy a new engine," says Dario Orlando."