In need of help!


New member
Oct 24, 2021
Toledo, Ohio
So last week I went to my local machine shop and was discussing some machine work needed done and if they could build the short block for me. When I started talk about the pistons he told me with the camshaft I'm putting in I would need to run a flat top with valve reliefs versus a true flat top piston. The camshaft I'm going to try in a 244/244 duration @ .050 and .518/.518 lift. I want at least a 10.25:1 CR. But what is everyone's opinion, is a true flat top piston like the W31s had (safely and common sense wise) possible?

Olds 307 and 403

Well-known member
Oct 4, 2018
Melville, Saskatchewan
Yes, you will be fine with that lift. For one, the Speedpro sit .025" below deck. It is the only stock stroke flat top I know of. The lift is only a bit over .500". Obviously you need an adjustable valve train with that cam. I believe lift doesn't become an issue unless you are in the .600" range with big duration. If you run these with a 60cc chamber and 0 deck, you will get 10.25 to 1. I am using them at 9.5 to 1 with a 68cc chamber. They only need a .013" mill for 0 deck, 1mm ring pack, .0025" piston to wall, half what Speedpro need. For you the .0035" for Racing may be more appropriate. Plus they are lighter and coated. The Molnar rods are also super nice and a direct fit SBO rod. The pins do need hone fitted to the rods.

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