TF's on a 318 ???? Oops, another 318 thread...

Dave_J said

OK, the 318 has a bit of shrouding issues. But that can be elevated somewhat with a bore notch. Pick your piston first. Then at TDC measure where the top ring stops. Go about 0.100" above that and make a mark. Then using a 340 head gasket, scribe around where the intake valve will be. Then using a round carbide, angle notch the bore down to your line of the piston ring mark leaving a 1/4 radii at the bottom. Go about 2.5 inches wide. De-bure edges.
Yes this will knock the compression ratio down, as will using the 340 head gasket bore. This is why you need to do the math before hand and buy the pistons CR a bit higher.

Click to expand...

Everyone seems to subscribe to using the head gasket as the limit to port or relieve to. IMHO this is not exactly correct especially for porting in the combustion chamber. For relieving the bore slightly should be OK for unshrouding, but in the combustion chamber you take it out real close to the gasket which can cause gasket problems. The other issue is the intake mixture hits a small ledge at the top of the bore which will cause some turbulence in a non beneficial manner. I would prefer to Dykem the cylinder head gasket surface and instal the heads on an MT block. Then scribe around the finished bores. This will give a smooth transition from combustion chamber to the cylinder, with only the small area between the difference between the diameter of the gasket fire ring and the bore.