Jordan1984

This is how they check for blown head gaskets, burnt/stuck valves, to make sure that it is blown or damaged and not something else. Its called a compression check. Take out the number 1 plug. Put the gauge into the number 1 plug. Crank the motor until the gauge reads at the highest point. Write it down. Do the same thing for cylinders 2 through 8. Add them up. Divide the number by the number of cylinders. This will give you a round about compression ratio. Example: number 1 cylinder - 9.5, 2 cyl - 9.6, 3 cyl 9.6, 4 cyl 9.5, 5 cyl 9.5, 6 cyl 9.4, 7 cyl 9.6, 8 cyl 9.5. This equals 76.2 total. Now divide 76.2 by the number of cylinders. 76.2 divided by 8 cylinders = 9.525. Your compression ratio is 9.5:1.

Tod74

Have you ever actually DONE a compression test? Or even held a compression gauge in your hand?

Just Curious.

I972Nova

I'd like to have one of those magic guages that tells you the compression instead of the cylinder pressure...lol... That must be the Master Mechanic brand...

fla1976

:idea: Oh yeah, the old divide by 8 rule.

With a compression average of 9.5, you should be able to run in the mid nines. ops:
Here are a few sites:
http://www.not2fast.com/turbo/compre...pression.shtml
http://www.bgsoflex.com/cr.html
http://www.carcraft.com/techarticles...tio/index.html

Jordan1984

Yes I have done many compression checks and figured compression ratio on this method. You take 1 plug out and put a fitting into the plug hole. The fitting has a vacuum hose that runs to the compression gauge itself. This procedure is in every automotive manual that I have and have been told by many mechanics to do this. Haynes, ford thunderbird, mercury cougar, 1989 -1997 haynes repair manual, chapter 2 part C section 3, cylinder compression check is what I am refering to. Get any manual and look it up, or ask any full time mechanic, not a weekend backyard mechanic.

MEMRACING62

jordan, I think your confusing presure with ratio, look at the links fla left for you above ( the car craft one explains it very well) that should clear up the confusion.

zipper06

This is too funny :lol: , It is vertually impossible to check/get the compression ratio, without knowing about 6 factors, IE stroke,bore,piston dome or relief, valve relief, gasket thickness, and the cylinder head volume. Below is another formula on how to calculate the compression ratio ans it includes all the specs. needed.

Zip.

http://www.wallaceracing.com/cr_test2.php

Jordan1984

Try it sometime. Go to the calculator and type in all your specs. Then try the way I told you to. Bet you are within +/- .1. I know what I am reading in the automotive manuals. It says cylinder compression check. It doesnt say cylinder pressure check. If you dont have a manual, buy one and look at it.

MEMRACING62

compression check is only useful to determine condition of cylinder. not the ratio. fla & zip left some great links for ya to clear up the confusion. if a mechanic is telling you that you can tell compression ratio from the guage, he is dead wrong!!

suicidebomb

Well now I see what the problem is...........