Author Topic: Compression Ratio  (Read 528 times)

Offline spitzerscott

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Compression Ratio
« 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

Offline noslin

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Re: Compression Ratio
« Reply #1 on: July 27, 2017, 12:11:11 PM »

Offline msundstrom

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Re: Compression Ratio
« Reply #2 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

Offline spitzerscott

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Re: Compression Ratio
« Reply #3 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

Offline wideopen231

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Re: Compression Ratio
« Reply #4 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.
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Offline spitzerscott

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Re: Compression Ratio
« Reply #5 on: July 27, 2017, 01:14:48 PM »
This is a 336 SBC

Offline Frontenginedragsters

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Re: Compression Ratio
« Reply #6 on: July 27, 2017, 04:56:56 PM »
This is the calculator I use:
http://users.erols.com/srweiss/calccr.htm
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Offline Roger

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Re: Compression Ratio
« Reply #7 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.

Offline spitzerscott

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Re: Compression Ratio
« Reply #8 on: July 27, 2017, 05:33:03 PM »
Thanks Roger, that's what I was looking for.