bansheeyfz Posted January 16, 2007 Report Share Posted January 16, 2007 My banshee has just t5s and a cool head with 21cc domes. if i switch to 19cc domes will i have to run race gas or no t i heard that is the most you'll be able to go before running race gas. also will i fell a noticeable difference switching from 21 to 19s? If i get a Mx port in the future will i have to run race gas then? Thanks Quote Link to comment Share on other sites More sharing options...
woodro77 Posted January 16, 2007 Report Share Posted January 16, 2007 it depends on your elevation , where do you live ? the closer you live to sealevel the more your compression goes up Quote Link to comment Share on other sites More sharing options...
bansheeyfz Posted January 16, 2007 Author Report Share Posted January 16, 2007 near philly Quote Link to comment Share on other sites More sharing options...
bansheeyfz Posted January 16, 2007 Author Report Share Posted January 16, 2007 is 93 octane alright Quote Link to comment Share on other sites More sharing options...
bada450r Posted January 16, 2007 Report Share Posted January 16, 2007 is 93 octane alright two words......compresion check......... :shoothead: :: Quote Link to comment Share on other sites More sharing options...
bansheeyfz Posted January 16, 2007 Author Report Share Posted January 16, 2007 well i figured that. Whats the high compression can you run without runnin race gas. 185? Quote Link to comment Share on other sites More sharing options...
letsgetthisdone Posted January 16, 2007 Report Share Posted January 16, 2007 ithink 150psi is the cut-off if you wanna run straight pump gas. Quote Link to comment Share on other sites More sharing options...
2003LimitedBanshee Posted January 16, 2007 Report Share Posted January 16, 2007 well i figured that. Whats the high compression can you run without runnin race gas. 185? It won't run long on pump at 185 psi. I kick near 190 psi (and +4 timing) at sea level and I run straight Trick Race Fuel. I'm not sure about woodro's statement. I think maybe I am just interpretting his explanation wrong. Compression psi goes up as elevation increases, but the same cc dome change will not net additional compression at a lower elevation over the higher elevation. Quote Link to comment Share on other sites More sharing options...
dajogejr Posted January 16, 2007 Report Share Posted January 16, 2007 It won't run long on pump at 185 psi. I kick near 190 psi (and +4 timing) at sea level and I run straight Trick Race Fuel. I'm not sure about woodro's statement. I think maybe I am just interpretting his explanation wrong. Compression psi goes up as elevation increases, but the same cc dome change will not net additional compression at a lower elevation over the higher elevation. Incorrect.... The same bike will have less cranking compression at a higher elevation than lower. Dome size is irrelevant. You lose roughly 10 to 18 PSI for every 1000 to 1500 feet of elevation...roughly. Big Red Rides at 7500 or 8500 feet, and he uses his own 16cc cut domes, to get him good compression. At or near sea level where I ride, I wouldn't even dream of running 16cc domes, it would put me into the 200's for PSI, and make my bottom end life very short lived... To answer your question, however, bada put it right. Compression check... There are NO rules, only educated guesses and guidelines. Here are the ones I go by, taking into consideration you run +4 timing. 150 or less, pump SHOULD be ok. 151 to 165, mix pump/race 165 or more, 110 octane, etc. Now...these are estimates. some may run more compression on less octane, some may run less compression on more octane. Bottom line is check the compression for a baseline starting point, and use a GOOD QUALITY tester, not an auto store el cheapo. Then, listen to your motor and check your plugs often. Quote Link to comment Share on other sites More sharing options...
2003LimitedBanshee Posted January 16, 2007 Report Share Posted January 16, 2007 Incorrect.... The same bike will have less cranking compression at a higher elevation than lower. Dome size is irrelevant. You lose roughly 10 to 18 PSI for every 1000 to 1500 feet of elevation...roughly. Big Red Rides at 7500 or 8500 feet, and he uses his own 16cc cut domes, to get him good compression. At or near sea level where I ride, I wouldn't even dream of running 16cc domes, it would put me into the 200's for PSI, and make my bottom end life very short lived... To answer your question, however, bada put it right. Compression check... There are NO rules, only educated guesses and guidelines. Here are the ones I go by, taking into consideration you run +4 timing. 150 or less, pump SHOULD be ok. 151 to 165, mix pump/race 165 or more, 110 octane, etc. Now...these are estimates. some may run more compression on less octane, some may run less compression on more octane. Bottom line is check the compression for a baseline starting point, and use a GOOD QUALITY tester, not an auto store el cheapo. Then, listen to your motor and check your plugs often. You caught my error, I guess that's what I get for responding after working all day late at night. Compression psi absolutely increases with a decrease in elevation. I completely typed the wrong angle. The statement in woodro's I was intending to address was that Red should see the same compression change as I would when I ride at sea level if we both went from 16cc to 18cc. In other words, if Red sees a 30 psi drop by going from 16cc to 18cc I should see a 30 psi drop as well, all else the same. Now, where I got caught with my pants down late last night, was that absolutely I will see a higher compression psi at 2000' vs. Red's 7500' if everything else is exactly the same on the bikes. My apologies; way to sound like a dumbass on my part. :: :: Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted January 17, 2007 Report Share Posted January 17, 2007 I run 19cc domes at 2500 ft elevation. I have an MX port job and have 150 psi compression both cylinders. My timing is set at +4 deg. I run 91 octane fuel. Liek every one said every motor is different. Quote Link to comment Share on other sites More sharing options...
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