there is a tool to do this

[Clem Z.]

called the "katech whistler" that calculates the CR by injecting air into the cyl. at TDC and a computer reading the frequency of the air coming back out to calculate the CR. work like blowing across the top of a pop bottle and you get different sounds by how much water,displacment, is in the bottle. this device was developed by GM for use in their engine plants to check the CR of the engines being built because of the stack up of machine tolerances could cause a CR problem

[Clem Z.]

this post should be with the CR question

http://72.14.209.104/search?q=cache:6vEhI_euxi4J:www.katechengines.com/corporate_services/whistler.php+whistler&hl=en&ct=clnk&cd=1&gl=us

[Terry F.]

Re: this post should be with the CR question

Clem, should I calculate a cr on my engine even though I am using factory style pistons and cam configuation? Terry

[Joe C.]

Re: this post should be with the CR question

CR = (Displaced Volume + Compressed volume)/Compressed Volume

Displaced volume = [3.1417 (bore/2)(bore/2)]/ stroke

Compressed volume = chamber volume + ring land volume + valve relief volume - piston dome volume + piston dish volume + head gasket compressed thickness + piston-to-deck clearance + annular volume between bore and gasket circle.

All variables should be measured.

[Duke W.]

Re: this post should be with the CR question

Not to nitpick, but what you say is compressed volume is usually written as "clearance volume", which is the TOTAL combustion chamber volume with the piston at TDC, which is a function of several variables. The best way to understand this is to use the online compression ratio calculator that I've referenced a zillion times.

One will see that deck clearance, head combustion chamber volume, piston crown volume, and head gasket thickness are significant variables, and even small changes in these variables can have a significant affect on as-built actual compression ratio, and the only way to know what the actual engine CR is is to HAVE ACCURATE VALUES for all these variables and run them through the calculator.

With the internet it's easy. Thirty years ago I had to do it all with a hand held calculator.

Duke

[Clem Z.]

go to this website for CR calculations and others

http://www.bgsoflex.com/auto.html

[Terry F.]

Re: go to this website for CR calculations and oth

Thanks, looks interesting and INTIMIDATING....

Terry