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| Maximum compression ratio before needing premium? https://slantsix.org/forum/viewtopic.php?t=46493 |
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| Author: | Daddiojoe [ Thu Sep 29, 2011 12:52 pm ] |
| Post subject: | Maximum compression ratio before needing premium? |
At what point do I need to go to a higher octane? I have a 9.5:1 ratio on my current engine, but I'm runnning propane, which is 108 octane. Planning on building another petrol engine.... Thanks, Joe |
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| Author: | Doc [ Thu Sep 29, 2011 1:45 pm ] |
| Post subject: | |
An 8 to 1 DCR (Dynamic Compression Ratio) is about the max for 87 octane pump gas. DD |
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| Author: | Daddiojoe [ Thu Sep 29, 2011 3:31 pm ] |
| Post subject: | |
THanks, Doc. Is that about what stock is? Joe |
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| Author: | DusterIdiot [ Thu Sep 29, 2011 4:44 pm ] |
| Post subject: | Lol... |
Quote: An 8 to 1 DCR (Dynamic Compression Ratio) is about the max for 87 octane pump gas.
I've gotten away with a bit more at 8.23:1 DCR but had to yard the timing back which makes for a gain and a loss (kept the mileage, but I'm sure I left some power out of it...), that engine was 10:1 SCR...DCR is a more accurate way to check how your engine is going to possibly perform, there are several calculators online to help. SCR is what is typically is used (stock mill is advertised in the 8.2:1+/- range, but can be anything depending on the year and vehicle). -D.Idiot |
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| Author: | Doc [ Thu Sep 29, 2011 4:45 pm ] |
| Post subject: | |
The DCR from the factory is usually in the 7.5 to 7.8 range. DD |
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| Author: | Daddiojoe [ Fri Sep 30, 2011 6:50 am ] |
| Post subject: | |
So a thinner headgasket would probably be the safest and farthest you'd want to go as far as compression mods if you wanted to keep using regular? Joe |
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| Author: | Doc [ Fri Sep 30, 2011 9:28 am ] |
| Post subject: | |
Measure, calculate and set your static & DCR compression ratios... or ... Make your "best guess" and take your chances. The "best guess" with a factory SL6, give it more compression. Using a stamped steel shim head gasket helps but not a lot... and you need really clean & flat surfaces to get those to seal well. My best "guess"... mill the head to get a 50 cc chamber size and use a Fel-Pro gasket. DD |
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| Author: | Daddiojoe [ Fri Sep 30, 2011 12:50 pm ] |
| Post subject: | |
Thanks again, Doc. Joe |
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