Online calculators generally offer a choice of entering all measurements in either inches or metric, except for the combustion chamber and piston dome volumes, which are always entered as cubic centimeters or cc.
Compression ratio pro#
Most gaskets, such as this JE Pro Seal unit, provide the gasket volume and compressed thickness values to help compute the CR.
The latter will help provide volume above the top ring, but this measurement doesn’t usually affect the final calculation significantly and is used only in very critical applications. There are a couple of high-tech calculators online that ask for even more, such as rod length and distance from the first compression ring to the top of the piston. But as the old saying goes, a computer is only as good as the quality of information it gets. Today, finding online calculators that quickly spit out the results is only Google click away. In the old days, calculating the CR meant getting out the slide rule (really long time ago) or working through a set of formulas on a hand-held calculator. Subtract the amount of fluid used from the calculated cylinder volume. Using a burette and clear deck plate, fill the cylinder with fluid and take note of how much was needed. In this example, the bore (4.600in) and exposed cylinder 1.5in equals 40.9 cc. Volume= (π) x (bore radius squared) x (exposed cylinder height). To calculate dome volume: first, position the piston a measured distance into the cylinder, making sure the dome is below the deck. And, if the power isn’t quite there, another pound or two of boost easily makes up the difference.” The tuning window widens and provides more of a safety envelope in the event of a fuel pressure or delivery problem, or even a bad batch of gas. “In forced induction (FI) applications, erring on the low side is much safer than pushing your luck on the high side. On the high side carries greater risk in tuning and potential component failure if appropriately better fuel is not used,” says Alan Stevenson of JE Pistons. “Too little compression will usually result in unmet performance expectations. write the number on the piston as your checking for easy comparison. Move the indicator to the deck plane of the piston to read how far the piston is below or above the deck of the block. First, bring the piston to TDC, then zero the dial indicator on the deck surface of the cylinder block. The compression ratio is affected significantly by the deck clearance volume, The distance between the piston crown at TDC and the height of the deck surface.