Compression formula?

[MILITISINVICTUS]

Does anyone know of the formula you would use to back into what compression ration pistons you have by inputting the psi readout of your compression test?

I have a stroker that's reading 190-195 across the board. I didn't do the build, so I'm not sure of the pistons' ratio. If someone recognizes these numbers, a shortcut answer for what my ratio probably is, is cool too.

 

[telnut]

Engine compression test has no bearing on engine compression ratio. Engine compression ratio is a ratio. How much air is compressed into what volume. To get comprssion ratio you need to know bore, stroke, cc of combustion chamber and head and type of piston, gasket thickness. You can not get ratio from compression pressure. Some imports will run a 9.5 to 1 compression ratio and read 200 psi on compression test. Some domestics can have a 10:1 compression and read only 150 psi on compression test. When doing compression test you need to take in to consideration altitude and air density.. Example would be an engine that compression test at sea level will read 150psi, however at 6000 feet the compression will read close to 130psi. Remember all reading in factory manuals are based on reading at sea level. A rule of thumb is compression pressure changes by about 3% per 1000 feet above sea level. Of course humidity and air tempreture can alter this. THis formula is a "rule of thumb"

Telnut

 

[CanadianTSi]

9:1 Pistons would be my guess.

 

[GVR4592]

There's an electronic device from Katech, called the Whistler, it can determine the compression ratio of an engine. They can usually be found at most large circle track events.