Dynamic compression formula

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Dynamic compression formula

Post  747JetMech on August 10th 2015, 6:26 pm

Guys

Is there a formula to figure out dynamic compression ratio? Is fuel octane chosen with dynamic or static compression?


Thanks
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Re: Dynamic compression formula

Post  supervel45 on August 10th 2015, 6:37 pm


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Re: Dynamic compression formula

Post  DanH on August 11th 2015, 10:42 am

want the real D comp ratio? when building the engine it can be got easy.

short block and cam dialed in,one head on (#1cyl) . lifters ,pr's, rockers on and adjusted.

bar crank over till intake valve is(just closes. now measure #6 piston from deak. that distance is now the stroke number. use that number and bore for cubic inch. the rest is just like finding static compression ratio.
That c/r is the real D/ratio

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Dynamic Compression

Post  69BOSS on August 14th 2015, 12:27 am

I have been playing around with the calculator and cam profiles, trying to get a dynamic ratio of 8.2 to 8.3:1 for a pump gas engine. One thing I found that I never thought about before is how much late intake valve closing point reduces cubic inch displacement. A 545 CI with a mild cam, intake closing at 71 degrees ABDC, reduces CID to just 403 CI. In comparison, a 466 CI street engine with an intake closing at 59 degrees has 379 CI. Only 24 CI difference. Take the 545 CI and close the intake at 81 degrees and the CID is only 360 CI.
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Re: Dynamic compression formula

Post  supervel45 on August 14th 2015, 12:41 am

So what HP did 1 point of static compression increase did a 545 with the same cam pickup?

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Re: Dynamic compression formula

Post  DanH on August 14th 2015, 4:53 am

69BOSS wrote:I have been playing around with the calculator and cam profiles, trying to get a dynamic ratio of 8.2 to 8.3:1 for a pump gas engine. One thing I found that I never thought about before is how much late intake valve closing point reduces cubic inch displacement. A 545 CI with a mild cam, intake closing at 71 degrees ABDC, reduces CID to just 403 CI. In comparison, a 466 CI street engine with an intake closing at 59 degrees has 379 CI. Only 24 CI difference. Take the 545 CI and close the intake at 81 degrees and the CID is only 360 CI.  
"only".more to it than the cubes at the d/ratio cubes

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