You would "travel" the piston down half and inch from true TDC, not just measure the piston to the top of the deck directly. Is this engine already assembled? If not, maybe you can test the half inch down fill volume and that will give you exact numbers. With those numbers in the calculator on the website, it comes out to 9.99 to 1, and that is including. 018" above the deck, assuming 9.6" deck height, and the numbers measured from 72bluNblu confirm this on his engine. But, the numbers say that "flat top" would sit about. If we treat that as a flat top piston, which typically has around 5 or 6 cc valve pockets, you would add the volume of that little step around the piston to the valve notch volume, and that is how they get 7.3 cc. Do you know for sure if yours was previously decked?Īs for the numbers, I think I agree with KB on this one, or at least they are pretty close. In the picture of post number 7, the deck surface appears to show markings from previous decking. You may need to adjust that clearance with a thicker head gasket. 018" over the deck like they're supposed to be you'll need to check your piston to head clearance if you run closed chamber heads. I ended up running a different head gasket than the one I gave the Tech and my head chambers ended up 1cc larger, so it calculated a little differently when I updated the gasket View attachment 1715876343Īlso, with the KB 243's if you do end up with the tops of the pistons. Instead, he told me to use a deck height of 0 and a 7.3cc volume, with that volume accounting for the protrusion and the valve reliefs. I'm not entirely sure where the 6cc volume comes from that they advertise, but the tech I spoke to at KB straight up told me not to use it.
030" protrusion, so the shoulder of the piston sits. The compression calculators I was using, including the Wallace calculator, had some issue dealing with the deck height and the piston volumes because of the way that piston is shaped. 018" over the deck (which is the spec with the stock deck height). I have KB 243's in my 340, they measured.
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