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PK2,

Yes, In a word I think the Honda, Nissan, Mitsu. motors are much stronger as a Hot rodding platform. They are also low compression so they adapt well to variable boost turbocharging. Complete sets of racing pistons, rods, cams, etc. are cheap and available everywhere. They are easy to keep cool and there is usually room under the hood for lots of HP add ons. It is not uncommon to get 200hp/liter on a built VTEC motor and have it hold together pretty well.

The 986 2.5L is a very highly developed, high compression N A motor. At 11/1 compression it doesn't adapt very well to forced induction (detonation is a problem). Essentially zero internal parts are available and there is no aftermarket for internal racing parts. The radiators are far away from the motor so it is harder to get rid of excess heat. And no room under the hood. From what I have seen I think that 100hp/liter is the ragged edge of a reliable performance envelope on this motor and you are already there.

Pushed to the breaking point, cause of death could be: blown head gasket, broken pistons, thrown rod, IMS failure, broken crank, failed main bearings, slipped cyl. sleeve, seizure due to overheat etc. The blown head gasket is the only one that is repairable. Quite a different story than a Chevy small block or Honda VTEC.

You are a pioneer. You are blazing a path over the dead bodies of others who have pushed the performance of the 986 and lost. I hope you succeed. This country was built by those who didn't accept conventional wisdom. It's your car. If you want it I say go for it. What would Chuck Yeager or John Glen say?