help on compression testing

im planing to compression test my 350 sbc useing the type of gauge that goes into the spark plug hole.

what i need to know is the formula used to go from bar/pis on the gauge into 9to1 or 10to1 ect ect compression ratio.

a chart or some e.g. would be a good help too.

thanks lee

 

You can't calculate static C.R. with only a compression reading. You need to know volume at TDC and volume at BDC, and do the math. A compression reading will only tell you psi, and that can reflect leakage by the rings or a bad head gasket, etc.

 

Look more for an even reading on all cylinders, as opposed to pressure.
Pull out all the plugs, disable the coil, crank each one equally. Right down the reading, move to next hole.

 

ok guys im trying to find out what the C.R. is on my motor its a fresh motor and i no the flowing info.....

head c.c.

head gasket thickness

flat top pistons

bore size

stroke

more help please i hope you can under stand what im trying to do.

thanks lee

 

You need a P&G tester to determine compression ratio.

http://www.precisionmeasure.com/test1.htm

Probably would be cheaper to tear down the engine if you really need to know the compression ratio.

 

Lee--

do you mean you "know" the following info?

If you do, then tell us what it is, and we'll help you figure out the compression ratio.

If it's a 350 with stock 3.48" stroke, and flat top pistons, the CR is probably about 9:1 if the heads are about 76 cc, or it's about 10:1 if the heads are about 64cc.

THe more details you can provide, the more accurate we can be.