[RKDinOKC]

Here is what I found.

5.0 liter 928 S3 - 296hp.
5.0 liter 928 S4 - 315hp, intake manifold and cam changes.
5.0 liter 928 GT - 326hp, cam changes.
5.4 liter 928 GTS - 345hp, stroked and detuned cams.

There are 4 different cam sets with the 5.4 liter GTS having the smallest lift and duration. A combination of the S3 exhaust and GT intake cams provide the most lift and duration both intake and exhaust while remaining within Porsche stock cam profiles. This produces a 50hp gain on the GTS 5.4 liter. This is considered a very reliable hp upgrade as it is still using basically stock Porsche components.

I am considering increasing the valve spring rate as a While You're In There because it would need to be done if I ever want to go to forced induction like supercharging or turbo in the future.

For me, chip tuning is a given for ANY performance car. There are slight differences in every engine that the stock maps can't possibly cover for maximum performance/economy and more so any time anything is done to the motor. The stock chips should run any motor well enough to break-in cams.

The 928 has a really cool chip tool called the SharkTuner. You plug it to the diagnostic port and using a laptop and a wideband 02 just drive around. It builds the necessary basic fuel and timing maps itself! Then you burn Eproms with the new maps, swap it out and you are good to go...faster.