|
PCA Member since 1988
Join Date: Feb 2018
Location: SW Washington State
Posts: 4,677
|
Emphasize what Ian said. Squish increases combustion chamber turbulence, which increases fuel mixing and flame propagation. It's not only important for racing engines, but for street engines, and for the same reasons--it makes the engine more efficient. In street engines I shoot for .030", and for low-rpm engines, I'll go lower, say .025" or even .020". People tend to think that the limit is stretching of the rod at high RPM, which will cause the piston to kiss the head, but IMO, a bigger concern is that the piston rocks across the wrist pin as it goes up and down. If you have very tight piston to cylinder clearances (and Porsche engines with aluminum pistons and cylinders do have tight skirt clearances), the piston will rock less, allowing you to run a tighter piston/head clearances.
However, since you are building a race engine, stick to what Ian recommended,
__________________
1973.5 911T with RoW 1980 SC CIS stroked to 3.2, 10:1 Mahle Sport p/c's, TBC exhaust ports, M1 cams, SSI's. RSR bushings & adj spring plates, Koni Sports, 21/26mm T-bars, stock swaybars, 16x7 Fuchs w Michelin Pilot Sport A/S 3+, 205/55-16 at all 4 corners.
Cars are for driving. If you want art, get something you can hang on the wall!
|