gains from porting/polishing heads??

[j.fro]

Anybody had the heads on an M96 ported/polished? If you have, what were the results??

[mikefocke]

Raby does the port and polish IIRC but only on his almost full race and much bigger displacement engines. Not at all necessary for his smaller DE/DD engines.

[edc]

A bit like an X51 power kit for the 986

[Gelbster]

Originally Posted by j.fro

Anybody had the heads on an M96 ported/polished? If you have, what were the results??

If you look carefully at the heads on the bench, they look very good in terms of air flow. It seemed to me that upgrading to the later style fuel injectors was the best simple ,inexpensive mod. Obviously you would need a valve job also but that is just maintenance.

[Smallblock454]

Hello,

as Gelbster said, i don't think you'll get much HP from ported heads.

At the moment we have some rebuilts over here in Germany. One guy has rebuilt his engine lately and i think he has also ported the heads of his 228 HP 2.7; besides some other things like intake mods etc. He is still breaking in the engine, so no dyno results. At the moment he is trying a very interesting approach by modifying the original Porsche 5-speed gearbox with Audi gearbox parts, so he will have a 20 - 15% lower gearing over all gears. Means the maximum speed of the car will be lower, but acceleration will be faster. Still not finished, but if he's successful this could be an interesting mod for track cars.

Regards, Markus

[edc]

Originally Posted by Smallblock454

Hello,

as Gelbster said, i don't think you'll get much HP from ported heads.

At the moment we have some rebuilts over here in Germany. One guy has rebuilt his engine lately and i think he has also ported the heads of his 228 HP 2.7; besides some other things like intake mods etc. He is still breaking in the engine, so no dyno results. At the moment he is trying a very interesting approach by modifying the original Porsche 5-speed gearbox with Audi gearbox parts, so he will have a 20 - 15% lower gearing over all gears. Means the maximum speed of the car will be lower, but acceleration will be faster. Still not finished, but if he's successful this could be an interesting mod for track cars.

Regards, Markus

Is that work a full gearset or a more simple approach of changing the final drive?

I've made enquiries in the UK re a lower final drive and whilst I want to do it I can't justify the cost right now.

[Smallblock454]

Hello edc,

his attempt is to use the gearset and differential of a relatively cheap Audi gearbox and put it into the Porsche gearbox. There are some open questions and i don't know if it will work. We'll see. At the moment he's working at it.

Regards, Markus

[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.

[specboxCO]

Originally Posted by Smallblock454

At the moment he is trying a very interesting approach by modifying the original Porsche 5-speed gearbox with Audi gearbox parts, so he will have a 20 - 15% lower gearing over all gears.

The 5 speed 986 transmission is an Audi 012. You can simply swap the output flanges and put a transmission with whatever gearing you want from just about any Audi or VW of the similar vintage.

[Jake Raby]

Today the smallest engine we build is a 3.8 liter, and every single one of them gets some form of port work. I seldom have ever used a stock port with our big bore engines.