I don't think that is a GM number or piston. A Google search on that number has it come up as a copy of the 11:1 '70 LT1 350 piston. There were some late "69 LT1 engines but they wouldn't come with an aftermarket piston. Some reference was made to them being "Ohio" pistons. Some said they are prone to breaking.
Those are what we used to call claimer pistons for circle track racing. They were mostly made by TRW and were a low cost cast piston that would make about 11 to 1 with a 58cc head. The claimer name was because in that class, if you were kicking every ones ass, they could protest your "stock" engine and buy your motor for 500 dollars. Good luck, -Abone.
Hard to tell from the pic, but are the two upper ring lands for 1/16" rings? That alone would make them forged. Do they have spirock grooves for full floating pins? They are "close" to the stock 70 LT-1 piston, but those did not have the flame travel notch yours have; they are a TRW provided copy (TRW made pistons for other suppliers with the suppliers part number). Forged, high compression, and what gas do you plan on using? That's my best guess from the pic. Cast pistons usually have a directional notch in the top of the piston that would face the front of the block. Butch/56sedandelivery.
Looks like the numer 3 piston but it could be the # 4 if you turn it over. Not likely a factory 350 piston look for markings on the inside that is your best way to indetify it.
im going to my buddy's machine shop now to change the rod bolts. the motor ran good before but the kid i got it from ran it without sealing the intake. he ran it a few days with water in the oil so i figured i would freshen it up.
its a hypereutectic (claimer) piston from ohio. 11.5 to 1 with 64 cc chambers. thanks again for the help
Thank YOU for the final info. (my old LT 350 had pistons like that, and I wondered what they were...)
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