pishta
I know I'm right....
I read that the 4 valve relief 'eyebrows' of a stock 273/318 piston were a given 7cc's of lost compression when doing calculations. Im here to debunk it: I took some modeling clay and filled one of the reliefs of a stock 273 piston them rolled a deep socket over it to make sure it was nice and filled. I then cut the excess off and was left with a totally flush piston top in that area. I pealed the clay out and dropped it in a 10ml syringe filled with 5ml of water. It displaced exactly .6ml of water, raising it up to 5.6ml (or 5.6cc) SO: the eyebrows are a paltry .6cc's each, for a grand total of 2.4cc's. If you factor in the area of the ridge at the circumference (.75mm X 292mm) , your only adding another .21cc's . So you get 2.6cc total 'dish' for a stock flat top 273 with 4 eyebrows. Now you can factor in your compressed head gasket where C is the compressed gasket in mm {.040" is 1.016mm) (C x 6647)X.001 to get ml/cc. That happens to be 6.75cc's but dont forget your bore size is the bore of the gasket, not the piston so lets look at a 4.080 MP .040 head gasket: 4.080 to mm is 103.63mm; that equals 8434 square mm x 1.016 x.001= 8.5cc's. For a grand total of 11.1cc's plus any negative deck height (0.58mm~4.25cc) you have added to the 58cc's of (my) stock 64 head. Stuff starts stacking up, eh?