[thstone]

The best that I can offer is that I did quite a bit of research into porting/polishing/valve grinding of the 986 2.5L heads in regards to cheating in Spec Boxster racing. I read everything that I could find online and talked to several engine builders and mechanics.

I concluded that there is probably something like a 10-ish hp gain in doing so (I would be concerned with a claim that said more than 15hp max).

With that being said, a 10-ish hp increase is meaningful in a Spec Boxster race car (and against the rules) where everyone runs the same engine, but may not be noticeable or worth the cost for a street car.