CIS Pistons vs Conventional Hemi Dome
 

Can someone enlighten me as to why Porsche designed the Odd shaped dome on a CIS equipped engine? It looks like it squishes the combustion charge away from sparkplug and the injector. If that is a good thing, why am I seeing people using s more conventional symmetric dome with two flycuts?

The combustion chamber is toward the plug to contain the pressure and spark.
The pistons with valve relief can use more aggressive cams. IE, Carrera cams spec for stock is 1.25mm
With after market pistons you can go as high as 2.0 with the same cams.
Early, or valve relief, pistons and S cams more aggressively set near 5.5mm opening
Bruce

Thanks Bruce, my 964 grind cams and euro 9.8 cr should be good, but WILL check the clearance.