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I have another Question: I want to get my motor 340 back to 10to1 comp. is the 70 340 pistons different from my 73 ones and will they give me my desired net of 10to1?
Yes sir. The earlier (71 and back) pistons have only 2 valve reliefs and a very slight dome that protrudes out of the bore at TDC. The 72 and 73 pistons have four valve reliefs and sit down in the bore a little at TDC. There is a big difference, so get familiar with it by looking at it or you may slip up and get the wrong piston.