[SpeedRacer64]

The cylinder head is off my car and I was surprised to see dish pistons...really resembling more of a diesel piston than a performance gas piston in design ?.. Moreover...there is some relief cut into the piston top...why not more to clear any issues with valve collision. The pictures were taken with my cell phone so quality is much to be desired...Flash or Pete...any interjection as to why Porsche designed the piston this way...flame speed...volume efficiency. Just curious...what type of piston do you use for performance applications?

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[flash]

i can't see the pic well, and i haven't seen the top of a piston yet, but it is very common to dish a piston to shape the charge

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[Lzachary]

The pistons are pretty trick for a street car fairly high compression and cut to allow just enough valve clearance. Your photos although not clear the pistons look very normal. Most 968 performance pistons ie turbos will use Porsche's turbo piston design with an even bigger dish for lower compression other the pistons that come with the car are as good as it gets.

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[FRporscheman]

The valve relief sizes are kept to a minimum to maximize compression, and keep the shape smooth, to allow the dish to do its thing. The dish is there to squish all the CC contents into a small volume right close to the spark plug. Then the cental plug, symetrical CC in the head, and the dish, act to ignite the mixture and there's a nice even flame front. This design makes it extremely resistant to knock and allows for such high compression like 11:1. You can boost this engine with 10psi and still have no knock.



I don't know what you mean about diesel pistons. The pistons in my 300TD have a much smaller dish, as they create 21:1 compression ratio.

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