Was wondering if someone can double check my math. I get a DCR that is worryingly low, and makes no sense. Im using the DCR calculator from this site; http://cochise.uia.net/pkelley2/DynamicCR.html I have also tried the Kbsilvolite method at 0.050" + 15, but it makes no sense since its an estimate at best taking the position from 0.050" when the valve is still open and adding 15? Dont know how they came up with the No. 15. Cadillac 500 bored 0.050 over. Bore: 4.350 Stroke: 4.304 Cyl Head Chamber CC: 76cc Piston CC (dish): 26.5cc Head Gasket thk: 0.043" thk Fire Ring on Hd Gskt: 4.357 Piston to Deck: -0.003" (proud) and entered as negative in the calculator. Rod Length: 7.1" See cam card attached; But adv duration: 308/308 Intake closes adv: 86 Intake closes @ 0.050: 54 LSA: 112 ICA: 112 I get a static compression ratio of 10.339:1 and a Dynamic compression of 6.71:1. That seems unusually low to me.
I'm no math expert or engineer, of course. But, that actually doesn't sound too far off if you've got a cam hotter than stock. Your numbers are pretty close to the example on the Wiki page: http://en.wikipedia.org/wiki/Compression_ratio#Dynamic_compression_ratio Hope that eases your worry, at least. - Freed
I got 6.70:1 using the Wallace Racing calculator, so I believe you are correct. In comparision, my Nailhead is right around 7.34:1 with a 9.3:1 static compression ratio and a Thumpr cam that has a IVC of 63* ADBC @ .006 lift.
I would feel much better if it was in the 7's. Its not an exact science and the data is not extensive, but my understanding of the ratio is that it is NOT the "be all, end all" or "the last word", but more of a tool. Secondly any kind of performance application aims to be as close to 8.0 as possible with 8.3 being on the limit of 91 octane capability. From what ive read, engines in the 6's have been described as "pigs" for power. Usually about 8.3:1 SCR stocker chevy's with a "hot cam". I also have a quench that is nearly ideally perfect. @ 0.040. The only thing that will put my mind at ease is to find someone using this cam, and see how it worked out in real world. This motor is intended for a street/strip car. I missed a few items in my original post like rod length. Im adding it now.
I get the exact same numbers as you. I would advance that cam, it is pretty big advertised. Putting it in at 108 ICL (4 deg advanced) I get a 7.0 DCR.
