Comp cams xe268h for 318
In the rebuild, I'd bet something like the Felpro standard head gasket were put in, which are quite a bit thicker than the originals. Just that change would make the Static CR drop from the ACTUAL 9.7-9.8 from the factory down to around 9.2. So AJ's numbers are likely higher than what you really had for cranking pressure and V/P.
I gotta root around Wyrm's info on how the factory actually measured 'advertised'....IIRC it was at .008" lift?? (Wish I could get his info on that matter memorized.) Meaning that at .006" it would be more like a 274-ish cam and driving more towards being sluggish in the lower RPM ranges. And if the stock cam had no ground in advance like almost all of the aftermarket hyd flat cams do, there is another factor; it would go in retarded typically 4 degrees versus most aftermarket cams if installed dot-to-dot.
I adjusted the comp to match the Mopar cam, as best as I knew how. I used 10/1 as you noted because I was comparing each cam to the other, so the base compression used is relatively unimportant. The factory cam,with the 114LSA, no matter how you slice it,will puke pressure back into the intake, 4 extra degrees over the 110LSA-Comp, when installed as described. While the numbers may not be dead nuts accurate, I believe the comparison is.
I did not take the headgaskets into consideration because the heads don't have to come off for a cam change.I agree that a 4cc change in headgaskets, would skew the results a half a point of compression on a 10.1 340-engine , so the Mopar cam would finish at 160@126VP still less than the 162/132 of the Comp (post#284)
You won't hurt my feelings if you rework the comparo, just keep an eye on the percentage VP change; that's what's important here. Per post #284 that would be 122/132 = .924 or the Mopar should be 1-.924=7.6% weaker on the bottom, from stall to about 3000rpm. I have no idea what that 7.6% would feel like, but I could guess, lol. The difference from 3.23s to 3.55s is 9.9%, and from 3.55s to 3.73s is 5.1%.
Just remember that VP is a diminishing ratio number that may start out at that 7.6% loss, but somewhere between 3000 and perhaps 3500, that VP disadvantage number may have shrunk to zero; I have not studied out how that works. But the 2psi pressure difference, while quite small tells more about what the power difference might be from peak to peak, which in this case looks almost insignificant. However, we don't know what these cams are doing between closed and open. I suspect the Comp will be faster, and trap more mixture, and then the 2 psi might be worth something as it increases the EFFECTIVE compression ratio which is a third way of measuring compression, and is constantly changing with throttle position and rpm. This is the most meaningful compression ratio, as it most closely relates to what the operator is experiencing.
Scr is fixed mathematically, and so is the Dcr. But Ecr is constantly changing just like VE.
