So you are only running .017 piston to head clearance? That 7.25 is confusing me a little. i'm assuming that is .00725 down in the hole?.295 to .305 most generally is going to be legal. I have had a .308 legal at 26.7 cc. Roll the engine to exact tdc. Measure the outside edge of the piston at 12/3/6/9 o’clock. Divide by 4. Add that number to the head gasket. Then measure the depth of the head from the gasket surface to between the valves. Add that to your numbers and you get a final that should be between 295/305. For instance: piston is 7.25. Gasket is 009. Head is 287. Total is 303.25. Cc is 26.7
There's a page in nine sheets, my Excel program, that will Calculate it for you. You need to know the bore and stroke.Is there a combination that will put you on the correct c/r. Such as 19cc head, .030 in the hole piston, .012 gasket. There seems to be a lot of variance between blocks and heads
Not sure if that was directed at me or the OP. I'm just trying to see how tight i can get away with. Typically on used motors i'm ending up with the piston is pretty far up the hole and the common gaskets wouldn't give enough Piston to head clearance. But if they are running them that close without issue then i can probably get away with a .009 or .014If stock class racing, you're chasing the wrong thing... Compression ratio is irrelevant. You have to meet the MIN CC check to be legal. Many different builders achieve this in many different ways... you can cut a ton off the head and use a thick HG or you can mill the block and have .002 (just stay under) piston pop up etc. Many different ways to skin the cat and all show up different on the dyno. Some do a little of both. Static compression really isn't a big factor in power anyway with these things. The cam and head flow and carb is where you should be looking.
The 7.25 was the average of measuring the piston in the hole at tech. 12/6/3/9 o’clock. Add them together and then divide by 4. Your numbers will be different. Where you get different total numbers between .295/.306 is the measurement I didn’t share. That is how far the valves are sunk in the head. That plays a role in the true cc legality. That is also why the number system is not always accurate. I have done so many and documented the valves to where I can get it close nearly all the time.you already posted that when this was originally brought up. My question was directed to Dyno Don. Thanks though.