So, I'm trying to determine the DCR of my engine. Keith Black ( http://www.kb-silvolite.com/calc.php?action=comp )and Wallace Racing ( http://www.wallaceracing.com/dynamic-cr.php ) are both showing a DCR of ~7.5. This is on the low side for performance I understand. But the Wallace page also gives a cranking compression of 145.5 PSI. I just checked my engine and got 175-177 PSI on every cylinder (except the ones with the blown head gasket ) This cranking PSI would indicate a DCR of 8.5 or so, I think. Anybody have any ideas? I have checked and rechecked my numbers: 4.080 bore, .040 gasket with 4.230 gasket bore, .010 deck height, 5cc pistons, cylinder head volume 72cc. I'm putting in 72 for IVC degree number, which is what camquest lists as seat to seat. I am running .020 lash, so should I be taking that out? When I plug in 50 degrees which is the .050 timing, I get right at 175 PSI cranking compression, which is what I'm at.
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Plugged the numbers into that one and still got 7.66:1 DCR. That would still give me around 145 PSI cranking comrpression, yet I'm running 175-177 PSI.
DuckRyder wrote:Use 68 for the heads and see what you get...
Had a buddy tell me that Comp Cams are advanced 6 degrees. Plugged that in with 68cc heads and got 7.97 DCR, 10.66 SCR. That DCR would still put my cranking PSI around 155. I plugged the numbers into the Wallace Racing calculator and got 8.29 DCR, with a cranking PSI of 166.48, which is still about 10 PSI low.
DCR is an inexact science, the Silvolite one in particular usually differs from other calculators. There is one that you have to download and is widely belived to be the most accurate.
As with any other calculator, the better the numbers you use the more accurate the results. heads blocks and pistons all vary from specification and really the best way to get them is to measure your engine (including degreeing the cam). If the block and or heads have been decked in the past it could account for your discrepencies.
To what end are you attempting to calculate this, you mention blown head gaskets, but does it spark knock or exhibit some other problem?
DuckRyder wrote:DCR is an inexact science, the Silvolite one in particular usually differs from other calculators. There is one that you have to download and is widely belived to be the most accurate.
As with any other calculator, the better the numbers you use the more accurate the results. heads blocks and pistons all vary from specification and really the best way to get them is to measure your engine (including degreeing the cam). If the block and or heads have been decked in the past it could account for your discrepencies.
To what end are you attempting to calculate this, you mention blown head gaskets, but does it spark knock or exhibit some other problem?
No other problems. Runs strong. I have decided the blown head gasket was my fault for using old bolts and not using an assembly lube. Just checking myself to see if my components were a good fit, as I didn't understand or calculate DCR when selecting components. Based upon my crakning compression and the way it runs, I'm thinking I have a pretty good setup. Thanks for the help.
) This cranking PSI would indicate a DCR of 8.5 or so, I think. Anybody have any ideas? I have checked and rechecked my numbers: 4.080 bore, .040 gasket with 4.230 gasket bore, .010 deck height, 5cc pistons, cylinder head volume 72cc. I'm putting in 72 for IVC degree number, which is what camquest lists as seat to seat. I am running .020 lash, so should I be taking that out? When I plug in 50 degrees which is the .050 timing, I get right at 175 PSI cranking compression, which is what I'm at.
