Calculating compression ratio

[J-1]

Is this an accurate formula / method?

http://www.csgnetwork.com/compcalc.html

Trying to get a parts list together for my rebuild.

Not sure on pistons, but will try keep it to 86mm

[MR2 Rich]

Compression ratio is overthought IMO. That calculator looks correct though.

[Fer fecks ache]

this is only ok for an in theory, calculation, it doesn't take into account, the space between, piston crown and top ring, etc, head chamber, and also the fact that each valve is ground differently, or even have dished faces, so cannot be a simple c/r calculation because of other variables like plug protrusion and even down to type of plug nozzle projection etc, if its that important use a plasti-guage and a pipet etc to do a proper job, the only real way is to build the engine and measure it dynamically as many things change the compression under working conditions, like how wet the cylinder walls are, and the most important is engine temp, the dynamic route is the only real way as if we could just calculate it accurately we wouldn't need knock sensors etc.

[bobhatton]

Is this an accurate formula / method?

http://www.csgnetwork.com/compcalc.html

Trying to get a parts list together for my rebuild.

Not sure on pistons, but will try keep it to 86mm

Yes that will work if you put in the correct measured info.

As the compression ratio is the only variable in an engine you need to get it right for your engine design.

Design your engine first, fuel to be used, power wanted, at RPM, cams to be used, turbocharger to be used, intercooler to be used, that will give you a boost to use and that will determine the compression ratio for your pistons.

[bobhatton]

Compression ratio is overthought IMO. That calculator looks correct though.

The compression ratio is the most important part of an engine design, get that wrong and the engine will never give the power it should.