FrontEngineDragsters.Org Forum

Technical => Matt Shaff's Engine Shop => Topic started by: spitzerscott on July 27, 2017, 11:47:38 AM

Title: Compression Ratio
Post by: spitzerscott on July 27, 2017, 11:47:38 AM

If a set of pistons is advertised at 12.5cr with 64cc chambers, and I have 58cc chambers what would I end up with for cr? I know there is a formula but I'm trying to do it the lazy way.   Thanks

Title: Re: Compression Ratio
Post by: noslin on July 27, 2017, 12:11:11 PM

http://www.gtsparkplugs.com/CompRatioCalc.html

try that maybe. 

Title: Re: Compression Ratio
Post by: msundstrom on July 27, 2017, 12:18:46 PM

The FIE web site also, Spud has a very user friendly Compression calculator. Think it bumps it a little over 1 point @ 58cc.
Mark

Title: Re: Compression Ratio
Post by: spitzerscott on July 27, 2017, 12:22:37 PM

The reason why I am asking is, without taking the engine apart I cannot fill in all the blanks. But I was told to add about 1 point. Just thought someone could confirm.   Thanks

Title: Re: Compression Ratio
Post by: wideopen231 on July 27, 2017, 01:01:23 PM

actual bore and stroke number will change outcome of clculatios. A bigger engines number will be totally different  than smallier engine. Larger engine  easier to build compression in.

Title: Re: Compression Ratio
Post by: spitzerscott on July 27, 2017, 01:14:48 PM

This is a 336 SBC

Title: Re: Compression Ratio
Post by: Frontenginedragsters on July 27, 2017, 04:56:56 PM

This is the calculator I use:
http://users.erols.com/srweiss/calccr.htm

Title: Re: Compression Ratio
Post by: Roger on July 27, 2017, 04:58:40 PM

336 small bocks are usually a 0.060” over 4” bore with a 3.25” stroke. With a piston dome of 13cc, a chamber volume of 64cc, along with a 0” deck height and a 0.041” thick gasket with a 4.1” diameter, that come out to 12.5-1cr. Put a 58cc chamber on that combination and that comes out to 13.8-1cr. Or something close to that.

Title: Re: Compression Ratio
Post by: spitzerscott on July 27, 2017, 05:33:03 PM

Thanks Roger, that's what I was looking for.