Safe compression ratio for 93 octane

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Oct 23, 2010 | 08:31 AM

redbird555

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From: Pompano Beach FL

Safe compression ratio for 93 octane

Hi guys my buddy and I are currently freshening up his ls1 its basically a stock rebuild as the car is a DD and makes several trips. So far its a stock ls1 rotating assembly with upgraded rod bolts ls6 cam and 799 heads. So I guess we could basically call it an ls6 conversion. I know that there are better cams out there for power but hes on a budget and the cam was free with the heads.. So anyway his pushrods looked like pretzels when we pulled them so they'll need to be replaced with hardened ones. Question is we want to mill the 799 heads down a bit to get a little more compression out of the engine. The 7999's have a stock chamber of 64.45 cc's i think? And from what I know they can be milled to a max of 59cc before the deck becomes to thin? So if we did that with a stock gasket i get a compression ratio of 11.3:1 with a .051 gasket? Does that sound about right? We're shooting for a good compression ratio for a little more power an better response without creating knock issues on pump gas so if anyone has some input please post up.

Oct 23, 2010 | 08:39 AM

01FbTaWs6

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what you need to worry about is the DCR, not the SCR. (Dynamic compression ratio, not static compression ratio)

The common consensus is not to go over 8.5 DCR. I ran mine at 8.9 DCR (which was about 11.5:1 SCR) and never had an issue, but I had a very good tune in the car.

Oct 23, 2010 | 08:42 AM

camz28arro

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There shouldn't be any knock issues at 11.3, some get away wit a little more like above though.

Oct 23, 2010 | 08:49 AM

redbird555

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thanks guys to calculate the SCR i was using a stock thickness from what i was told was .051 for a mls gasket along with a 3.91 gasket bore does that sound right? Also how can I calculate dynamic compression all the formulas i found were giving me scr.

Oct 23, 2010 | 08:51 AM

01FbTaWs6

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I used to have the program, but have since switched computers. Do a search on here for the program. And i believe that stock thickness sounds correct.

Oct 23, 2010 | 09:00 AM

redbird555

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ok no prob i found the calculator here.http://www.kb-silvolite.com/calc.php?action=comp but i keep getting a dcr of 9.5 on a stock ls6 spec chart using 64cc for the heads 3.89 bore 3.91 head gasket bore 3.62 stroke and 6" rods along with 42 degrees for the intake closing point on an ls6 which is what i was told it was. I cant see where I m going wrong lol.