mgrey Posted August 13, 2011 Report Share Posted August 13, 2011 so i have big dune ported stock cylinders running 19cc domes but only pushing 130 psi. if i bump up to 17 or 18 cc what would my new comp. psi be. is there a cutoff psi for 91 oct fuel ? any help would be appreciated Quote Link to comment Share on other sites More sharing options...
coryv4 Posted August 13, 2011 Report Share Posted August 13, 2011 so i have big dune ported stock cylinders running 19cc domes but only pushing 130 psi. if i bump up to 17 or 18 cc what would my new comp. psi be. is there a cutoff psi for 91 oct fuel ? any help would be appreciated ur compression is low 19cc domes might be time for new rings Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted August 13, 2011 Report Share Posted August 13, 2011 (edited) x2 your compression sounds low with those domes, but I don't know your elevation. Check out the chart at the bottom of the page on the link to get an idea of what your compression should be with 19cc domes based on your elevation. I think the cutoff for 93 octane pumpgas is 150-160psi or so, depending on how advanced the timing is. http://www.nossmachine.com/banshee_heads.htm Edited August 13, 2011 by SuprSlow50 Quote Link to comment Share on other sites More sharing options...
AKheathen Posted August 14, 2011 Report Share Posted August 14, 2011 wtf is "big dune" port style? dune/drag? anyways, elevation will play a factor, but if your cyls are within 5psi of each-other, then your rings should be just fine. cranking compression is pretty much just for checking ring/piston condition. you can put out 130 and still be at the limits of pump fuel, and you can crank near 180 and still be safe. so, post your elevation, and a better porting description, and the compression ratio will decide Quote Link to comment Share on other sites More sharing options...
Dgrey Posted May 5, 2012 Report Share Posted May 5, 2012 Hey, the fool posting this is my brother. His elevation is sea level if that helps diagnose the problem. Glamis and Gordon's well is where we roll. Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted May 5, 2012 Report Share Posted May 5, 2012 i agree that the compression should be higher than that with 19cc at sea level. sounds like topend needs freshed up. Quote Link to comment Share on other sites More sharing options...
special06shee Posted May 5, 2012 Report Share Posted May 5, 2012 when i was running a "big dune port stock cyl." i had 20cc domes and had 155psi in both cylinder and had no promplem with 93 pump fuel! i also think you should give it a fresh top end.. 130 seems really low! Quote Link to comment Share on other sites More sharing options...
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