Loc Posted May 16, 2011 Report Share Posted May 16, 2011 So after the build my compression is right at 140 on each cylinder. What should it be 421 Cub with 20cc Domes 1400ft elevation Quote Link to comment Share on other sites More sharing options...
Boston Posted May 16, 2011 Report Share Posted May 16, 2011 what octane you going to run? Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted May 16, 2011 Report Share Posted May 16, 2011 what octane you going to run? id say right around 140-145 is where you should be at so you sound about right... Quote Link to comment Share on other sites More sharing options...
Loc Posted May 16, 2011 Author Report Share Posted May 16, 2011 I am going to run avgas 100LL. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted May 16, 2011 Report Share Posted May 16, 2011 I am going to run avgas 100LL. if your going to run 100ll then you should be able to run more compression than that....should be able to run around 150ish mark. Quote Link to comment Share on other sites More sharing options...
Loc Posted May 16, 2011 Author Report Share Posted May 16, 2011 This may be a dumb question but how do I raise the compression now. Would I have to have new domes cut for the cub. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted May 16, 2011 Report Share Posted May 16, 2011 This may be a dumb question but how do I raise the compression now. Would I have to have new domes cut for the cub. correct.....new domes for your coolhead. id call a site sponsor and have them cut them.....that way you know they are correct (as oppose to trinity) and they can tell you what cc you can safely go down to in order to raise your compression based on your cylinders\compression\and fuel Quote Link to comment Share on other sites More sharing options...
crazycanuck Posted May 16, 2011 Report Share Posted May 16, 2011 So after the build my compression is right at 140 on each cylinder. What should it be 421 Cub with 20cc Domes 1400ft elevation you sure they are 20cc?? 140 psi is really low. you should be arond 170-175psi with 20cc domes @ 1000ft Quote Link to comment Share on other sites More sharing options...
shakar Posted May 17, 2011 Report Share Posted May 17, 2011 i run ported stock with 20cc domes .they put me at 150 psi. i think porting lowers the comp abit?? Quote Link to comment Share on other sites More sharing options...
Loc Posted May 17, 2011 Author Report Share Posted May 17, 2011 No port work at all. I am thinking that the rings may not completly set. I am going to run it for a bit then check the comp again. Quote Link to comment Share on other sites More sharing options...
slacker1bob Posted May 18, 2011 Report Share Posted May 18, 2011 No port work at all. I am thinking that the rings may not completly set. I am going to run it for a bit then check the comp again. My 421 was 135psi with 24cc domes, so something seems wrong with yours, and I dont think the rings are gonna settle enough to get it where it should be. Also, 145psi can still handle 91 octane(according to Brandon at Wildcard racing) so you can definately have more compression with 100octane Quote Link to comment Share on other sites More sharing options...
tedd1 Posted May 18, 2011 Report Share Posted May 18, 2011 So after the build my compression is right at 140 on each cylinder. What should it be 421 Cub with 20cc Domes 1400ft elevation What is your squish? What thickness base gasket? Quote Link to comment Share on other sites More sharing options...
Coupelx Posted May 18, 2011 Report Share Posted May 18, 2011 No port work at all. I am thinking that the rings may not completly set. I am going to run it for a bit then check the comp again. how much have you ran it? if all you did was idle around then chances are the rings didnt seat and its likely they never will. The last few times i put mine together the compression didnt change drastically between the time i assembled it and after i rode it the first time. make sure your jetting is close and go rip on it a little bit. what gaskets did you use? Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted May 18, 2011 Report Share Posted May 18, 2011 as canuck said 170-175,but check the domes i have gotton mislabled domes more than once Quote Link to comment Share on other sites More sharing options...
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