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Originally Posted by aws View Post
The obsolete Hemispherical head design also benefited by the lower compression of a flat top piston.
The greatest weakness of the 911 engine combustion chamber is the offset placement of the spark plug. It's not as big a liability in the turbo engine as it is in a n/a high compression 911 engine due to the flat top piston and the superior atomization of the turbulant mixture that a turbo provides.

Originally Posted by aws View Post
My opinion is the longer stroke (76.4) compliments the rev range of the larger displacement turbo engines and adds displacement without increasing the bore. The weak point in these engines is the cylinder to head connection and the larger bore (100mm) cylinders just do not have enough material to insure a bulletproof seal. The largest bore size the factory raced in the 935 days was 97mm---for a good reason.
When OEMs design engines the bore and stroke is primarily set by the area that the drivetrain has to fit into.
Increasing stroke puts additional stress on the crankshaft and increases parasitic friction. The 935 engine had to be based on the stock 911 engine per regulations, so the factory was stuck with the stock case and the 97 mm bore.
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 12-11-2011, 04:37 AM
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