039-inch-thick gasket-bagging an ideal quench clearance (see below) in the bargain.Afr 315 heads. This will net a 9.3:1 compression with higher-flowing 360 heads, or over 10.2:1 with late-model 302 or Magnum heads using a standard. The same 318 with a set of Keith Black PN 167 pistons can be set to zero deck with a little block milling. 025-inch-thick MP gasket will just score an 8.6:1 ratio, but now the pushrod geometry is messed up, the intake face will need to be milled, and you've spent more money than you would have by getting higher compression pistons to begin with. There's no way to make power at that ratio. With standard 64cc 318 heads, you're looking at 8.0:1 compression, while a set of higher-flowing 360 heads drops the ratio to 7.75:1. The valve clearance notches cost another 1.5 cc. These have a compression height of 1.720 inches, putting the piston a good. Take, for instance, a stock-replacement 318 cast piston. Typical low-cost, stock-replacement, flat-top or dished pistons may look like a bargain, but the price you pay in compression ratio is anything but cheap. For the typical stock-stroke, pump-gas small-block, a zero-deck piston is usually the best choice. When building an engine, one of the most important choices is selecting the correct piston for the job. Since an uncut Mopar small-block cylinder measures 9.600 inches from the crank centerline to the deck, and our up-stroke/rod/piston numbers add up to 9.583, the pistons should be. Now, if we are considering a Speed-Pro H116CP piston, which has a compression height of 1.670 inches, we add that in to get 9.583 inches. Add the length of a standard small-block rod at 6.123 inches and you get 7.913 inches. Half of that is 1.79 inches, which is the up-stroke from the crank centerline. For example, a 360 has a stroke of 3.58 inches. After that, subtract the deck height to get the piston deck, or how far down in the hole the piston should end up at TDC. Add half the engine's stroke to the rod length and the piston's compression height. Estimating the piston deck height is fairly simple. A piston with a short compression height will sit lower in the bore as the crank reaches TDC. Compression height is the distance from the centerline of the wristpin to the top deck of the piston.
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