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Generation III Internal Engine
1997-2006 LS1 | LS6
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Old 10-23-2010, 08:31 AM   #1
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Default 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.
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Old 10-23-2010, 08:39 AM   #2
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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.
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Yeah your BIG stall, gear ratio, and tire size and your goals put you in or on the "kill" mode column. LOL
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Old 10-23-2010, 08:42 AM   #3
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There shouldn't be any knock issues at 11.3, some get away wit a little more like above though.
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Old 10-23-2010, 08:49 AM   #4
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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.
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Old 10-23-2010, 08:51 AM   #5
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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.
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Old 10-23-2010, 09:00 AM   #6
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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.
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Old 10-23-2010, 09:00 AM   #7
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here you go, here is 2 links. I havnt used either, but others here have.
http://www.kb-silvolite.com/calc.php?action=comp

and this one you can download it at the bottom of the page:
http://www.empirenet.com/pkelley2/DynamicCR.html
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Old 10-23-2010, 09:01 AM   #8
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yeah, thats not right. LOL
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Old 10-23-2010, 09:04 AM   #9
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make sure you add the 15 degrees
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Old 10-23-2010, 09:10 AM   #10
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I am at 11.4 to 1 and have no problems ... it is all in the tune and having a nice tight quench ..
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Old 10-23-2010, 09:10 AM
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93, commpression, compresion, compression, dcr, dynamic, engine, good, ls1, needed, octane, ratio, ration, safe, whats


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