DSM1290 Posted December 24, 2006 Report Share Posted December 24, 2006 I'm trying to put together a 440. And i'm wondering if 12.5:1 is to high of a compression for 93 octane. If so, what would be the highest you would recommend? Quote Link to comment Share on other sites More sharing options...
AJ Posted December 24, 2006 Report Share Posted December 24, 2006 11:1 is the highest you should go, 11:5 if you retard the timing alot. thats if you use aluminum heads. i'm not sure about cast iron i think its not recomended to go past 10:5 Quote Link to comment Share on other sites More sharing options...
Dave1647545494 Posted December 24, 2006 Report Share Posted December 24, 2006 compression ratio is not really the main issue.... its cylinder head and piston design that really limit what you can do (quench area).... with the right combination of parts 12.5 and evnen higher compression ratios are possible if your using mostly off the shelf stuff AJ is correct stay around 11:1 Quote Link to comment Share on other sites More sharing options...
Farkas Posted December 24, 2006 Report Share Posted December 24, 2006 I'm runnin' 93 octane and 11.7:1 compression in the Corolla pretty good, but I'd be interested in seeing how well my car runs on 104 octane. Quote Link to comment Share on other sites More sharing options...
AJ Posted December 24, 2006 Report Share Posted December 24, 2006 your corolla also has a knock sensor and retards timing Quote Link to comment Share on other sites More sharing options...
desperado Posted December 24, 2006 Report Share Posted December 24, 2006 This will almost sound silly, but but build the fuel system to run E85. It's 105 octane and is pretty difficult to get to detonate. E85 is cheaper than moose piss 87 octane and will make power like race fuel. Quote Link to comment Share on other sites More sharing options...
98fiveseven1647545503 Posted December 24, 2006 Report Share Posted December 24, 2006 Shouldn't this be in the TECH SECTION???????????? Quote Link to comment Share on other sites More sharing options...
koolrayz Posted December 24, 2006 Report Share Posted December 24, 2006 The valve events can have more to do with the answer to your question than anything. Your asking what static compression ratio you can get away with on pump gas (SCR) when actually It's the dynamic compression ratio DCR that tells the real story. Cam overlap, bleedoff etc can allow a low enough DCR to allow you to run over 12:1 on pump gas. This Is a complex subject that is certainly beyond my knowledge, But i suggest you employ a true expert when trying to select components for an engine so that they truly work together. Quote Link to comment Share on other sites More sharing options...
Guest powers Posted December 24, 2006 Report Share Posted December 24, 2006 The valve events can have more to do with the answer to your question than anything. Your asking what static compression ratio you can get away with on pump gas (SCR) when actually It's the dynamic compression ratio DCR that tells the real story. Cam overlap, bleedoff etc can allow a low enough DCR to allow you to run over 12:1 on pump gas. This Is a complex subject that is certainly beyond my knowledge, But i suggest you employ a true expert when trying to select components for an engine so that they truly work together. excellent advice. Quote Link to comment Share on other sites More sharing options...
Guest Removed Posted December 24, 2006 Report Share Posted December 24, 2006 The valve events can have more to do with the answer to your question than anything. Your asking what static compression ratio you can get away with on pump gas (SCR) when actually It's the dynamic compression ratio DCR that tells the real story. Cam overlap, bleedoff etc can allow a low enough DCR to allow you to run over 12:1 on pump gas. This Is a complex subject that is certainly beyond my knowledge, But i suggest you employ a true expert when trying to select components for an engine so that they truly work together. very true, theres a guy running around in a older nova, 14.5 to 1 406. drives it everday on 93 octane, and at the tracks drops in the race gas and turns the timing back up. Quote Link to comment Share on other sites More sharing options...
Farkas Posted December 25, 2006 Report Share Posted December 25, 2006 your corolla also has a knock sensor and retards timing I'm glad you know all about my car.. Sorry to break it to you bud, but my car doesn't have a knock sensor nor an ECU. Quote Link to comment Share on other sites More sharing options...
AJ Posted December 25, 2006 Report Share Posted December 25, 2006 so did you retard the timing slot to stop the pinging? sorry i don't mess with imports or anything less than 8 cylinders for that matter. Quote Link to comment Share on other sites More sharing options...
Farkas Posted December 25, 2006 Report Share Posted December 25, 2006 I'm running somewhere between 30 and 32 degrees(IIRC) retarded, static timing. It's currently locked out because I don't have a vacuum advance distributor, but that's soon to come once I can source one compatable with the 4AG distributor. Quote Link to comment Share on other sites More sharing options...
desperado Posted December 28, 2006 Report Share Posted December 28, 2006 I'm running somewhere between 30 and 32 degrees(IIRC) retarded, static timing. It's currently locked out because I don't have a vacuum advance distributor, but that's soon to come once I can source one compatable with the 4AG distributor. You do relaize that retarded is After top dead center, meaning that the piston would already be moving down the stroke before you fire the ignition. Us silly V-8 guys tend to run our timing advanced, firing before TDC. Quote Link to comment Share on other sites More sharing options...
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