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Registered
Join Date: Jul 2005
Location: Cleveland, OH
Posts: 1,371
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CR change by shaving heads
Anyone have a formula(s) for calculating what you'll get for a new compresison ratio by knowing original compression ratio and motor size and shaving some value of heads?
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12-22-2009, 02:57 PM
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harold
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Stroke volume= Vs
Combustion volume = Vc CR (compression ratio) = (Vs+Vc)/Vc (if you know the CR you can determine the Vc) Shaved height= H delta Volume trough shaving = Vd= (0.25**Dē)*H =3.14 and D is cylinder diameter New Cr = (Vs+(Vc-Vd)/(Vc-Vd) hope this will help (and this is correct...) |
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12-23-2009, 02:37 AM
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Registered
Join Date: Jul 2005
Location: Cleveland, OH
Posts: 1,371
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Yes that make sense... I was forgetting Vc in the numerator of CR in what I was doing. Below is example for 993 for shaving 0.010" to 0.020" from heads. Frankly I was surprised at how much CR went up.
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12-23-2009, 04:21 AM
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harold
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yes, the effect goes up exponential with the CR. I was doing this calculation on a 3.3 turbo with a CR of 7.5 and there the effect is not that big.
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12-23-2009, 05:43 AM
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Woodland Hills, CA
Join Date: Dec 2008
Location: Southern, CA
Posts: 634
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And then there is valve to piston clearance and deck heighth checks...
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12-23-2009, 09:39 AM
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