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Restoration / Re: 302 engine build piston recomendations
« on: September 12, 2012, 02:17:19 AM »
First design 302 pistons used the narrow ring, '67 up to very early '68, when it was changed to the wider ring groove/second design piston. I'm pretty sure as I have the .030 over early '68 design in my '68 Z engine on the stand (hand filed the rings myself) - like yours, it won't see that many miles, so I decided to use them. They look different (see Jerry's book if you haven't already) but I like 'em. Second design 302 pistons used the wider ring, obviously, plus floating pins instead of press fits. I was fortunate enough to buy a NOS '68-9 set from GM right after they were discoed - wish I could have bought a bunch of them.
Biggest difference between the hypereutectics and the forged piston is piston growth - the cast pistons don't expand near as much as the forged ones under use, and are more stable/seal better in the bore, and don't require as near as large of a bore (read as skirt clearance), therefore less blowby. On the other hand, as was mentioned, I don't trust them at the higher rpm ranges (piston manufacturers would probably not want to hear that from anyone !)
The third set of 302 pistons I have is a set of forged Manley 12.5:1's - I actually ran them on the street in the 302 for nearly 30K miles - of course, I was putting 100+ octane leaded Union 76 gas in the tank at the time - '73-'75. The look exactly like the std. GM 302 pistons, except taller dome, and were floaters themselves. Made a liar out of my machinist - he said I'd pound the mains out of it within 10K miles - bearings still look brand new - plus you could have probably run kerosene in it and it wouldn't have complained.
Just some opinions -
Biggest difference between the hypereutectics and the forged piston is piston growth - the cast pistons don't expand near as much as the forged ones under use, and are more stable/seal better in the bore, and don't require as near as large of a bore (read as skirt clearance), therefore less blowby. On the other hand, as was mentioned, I don't trust them at the higher rpm ranges (piston manufacturers would probably not want to hear that from anyone !)
The third set of 302 pistons I have is a set of forged Manley 12.5:1's - I actually ran them on the street in the 302 for nearly 30K miles - of course, I was putting 100+ octane leaded Union 76 gas in the tank at the time - '73-'75. The look exactly like the std. GM 302 pistons, except taller dome, and were floaters themselves. Made a liar out of my machinist - he said I'd pound the mains out of it within 10K miles - bearings still look brand new - plus you could have probably run kerosene in it and it wouldn't have complained.
Just some opinions -