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Re: 318 Poly Pistons

From: Hank Dozier
Date: March 18, 2002


Actually, if you were to profile trace any piston made in the last 20 years, with rare exception it would NOT be round. The pistons are cam ground to an oval profile to accomodate the loading and resulting temperature difference found in usage. So...round bore does not equal round piston. As for rings, if the diameter is the same and the thickness of the ring correct for the piston groove, you can substitute. I have used BUICK moly pistons in a DeSoto 341 with a 0.020 inch overbore (3.78 + 0.020 = 3.800). This way, if you want to use chrome-moly, or maybe the "zero-gap" type rings, you can. Just make sure you get an accurate measurment on the ring thickness, or recut the grooves in your piston for the thicker ring, if not too much thicker. The LA pistons do not have the correct valve relief pattern as made. You can get non-relieved LA pistons (specify the compression height as calculated to give you the CR you want) and get them relieved by a machine shop. Hope this somewhat helps.


Last changed: July 19, 2018