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Check the compression distance. The Diamond piston you linked to has a 1.32" CD, This would be for the 3.75" stroke 6.768" rod engine.

FWIW, those pistons in a stock stroke / rod 400 with would have the piston sitting 0.612" below the deck, and with 84 cc heads new a whole 4.24:1 compression ratio.

Depending on the head volume you are using, stock flat top 400 pistons are already a low compression design.

The stock replacement flat tops have a compression height of 1.812" and the piston sits 0.120" below the deck at TDC. with 84 cc heads and 0.040" head gasket the compression ratio is 7.75:1.

For the stock stroke/rod combination there is not much of a selection of off the shelf pistons. For what you are doing, you will likely need to order custom pistons.




I have 72cc indy big ez's full cnc heads and i need low compression forged pistons for a turbo appication. I would ideally like to have 8.5 to 1





The pistons would prob have to be custom but do you realize how much those pistons would weigh and how tall of a compression height they would be, and then put them boat anchor pistons under a nice set of big ez's not a good idea in my opinion. I would sell your rods and find you some 440 length rods with a .990 pin and use the pistons you posted up top.

One day I will have something cool here.