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

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.