![]() This will allow you to put in all of the raw measurement values and it will compute all of the volumes and produce a CR automagically. If you don't want to go through all the pain of figuring this out for yourself, you can do a search online for a compression ratio calculator. What is the easiest thing to plug it with? A spark plug. If the hole isn't plugged, the liquid would run out. The way you measure the combustion chamber is with liquid. “If everything else is well-matched, a difference in 0.1 of ratio is negligible for anything shy of maximum effort professional racing.”Īs for the volume of the spark plug hole/spark plug, this is included in the combustion chamber volume. “Too many people get hung up on tenths of a point in CR but fail to understand the effects of fluid dynamics due to appropriate cam selection and phasing, for example,” says Stevenson. In practice, though, this area is so insignificant it won't make a difference unless you are in full race mode. If you REALLY wanted to get technical about things, you'd also include the area from the top of the piston to the top of the piston ring. Obviously, the stricter you are when calculating the separate volumes the better the final value will be. The number calculated is the static compression ratio, expressed as CR#:1 (swept volume + clearance volume) / clearance volume.Once that is added up, add the number to the total displacement, then divide this by the first number.Ĭlearance Volume = Head gasket volume + combustion chamber volume + piston dome volume + piston deck clearance volume This number would be used in both sides of te equation. Due to data compression, the actual data transmission rate or throughput (see below) may be higher. Add up all the volumes besides the displacement. are chosen in case of poor signal-to-noise ratio. Once you have the numbers, figuring the CR is fairly basic math. The piston deck clearance volume is the distance between the top of the piston at TDC and the top of the deck. This is usually provided by a piston manufacturer to help aid in figuring out the CR. This calculator will calculate both Static and Dynamic compression ratio Compression Ratio is the ratio of an engines cylinder volume vs. The piston dome volume is considered either positive or negative. ![]() You need the head gasket bore diameter, which may be slightly different from the cylinder bore diameter, and the head gasket compressed thickness to account for the space between the deck and the cylinder head. You use the cylinder bore diameter and the crankshaft stroke length to figure out the swept volume of a single cylinder. The measurements which are needed to figure these things out includes: The compression ratio (CR) is the ratio when comparing the volume of the cylinder above the piston when the piston is at BDC as opposed to when the piston is at TDC. well, it doesn't really matter, because the math works the same either way. You also ask how they calculate the CR ratio theoretically & practically. There is a dynamic CR, but that's a discussion I'll leave for a different question. Also, most given compression ratios are a static compression ratio (CR). In practice it becomes a little more difficult. ![]()
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