Lethaface Posted March 4, 2007 Report Posted March 4, 2007 Long story short, had a guy tell me yesterday that my 17cc domes may be to much compression for my new cub motor and that i may blow o-rings out on my cool head..Also was told that it may be to much for my 110 leaded race gas.. Anybody ever heard encountered anything like that?? Dome recommendations really seem to vary from one person to the next.. I have heard throw as much compression and timing at it as you can all the way to keep it in the 160lb range because the cub motors seem to perform better.. Anyways I'm gonna be running 110 leaded race gas, with a 4 degree timing advance at 2,000 feet elevation.. I have had two other sets of ported stock cylinders on 17cc domes that put out 170-185 lbs of compression.. I know the added stroke and volume of the cylinder is gonna make for more compression, I'm mainly just making sure i'm not going to ruin the first trip out over a $50 pair of domes thats so easily replaceable..So is anybody out there running 17cc domes on there 421?? Thanks, Letha Quote
Bansh-eman Posted March 4, 2007 Report Posted March 4, 2007 as long as you have the right squish you should be good 175 lbs is very common... and at an alt of 2k should be good... i know for sure 110 oct with 175 lbs is fine... im at sea lvl but im going with either 18 or 19 domes in this build... Quote
Lethaface Posted March 4, 2007 Author Report Posted March 4, 2007 I havn't even got a chance to check the squish yet..I am waiting on a ez change clutch cover so i don't even have any fluids in it as of yet.. Quote
moneybags Posted March 4, 2007 Report Posted March 4, 2007 My 421 cub runs with 19cc domes and has 175PSI in both cyclinders. It runs on VP 110 oct. I am also at sea level. I dont know what the squish is but the motor was built by passion racing. Dont know if any of that helps you. Quote
dajogejr Posted March 4, 2007 Report Posted March 4, 2007 Keep the squish in the low to mid 40's, you'll be fine. I ran 185PSI and a SHIT TON of timing on my bike, Jer...and 110 octane was fine. As long as you're doing it all right, cubs love compression and timing. Quote
Handyman Posted March 4, 2007 Report Posted March 4, 2007 I'm running 20cc domes with 175 psi at 200 feet above sea level...i also have a set of 17cc domes that will run about 200+psi at my sea level and that will be fine on VP 110 octane.. Quote
bansheeseat$$ Posted March 4, 2007 Report Posted March 4, 2007 Lethaface, I run 18's in my cub and have 180 psi at 4500 feet with 113 octane and +4 on the timing and don't have any problems at all.I'm suprised that some of these guys are only at 175 psi at lower elevations with there cubs.A little secret though,Dome angle is very important in the squish and compression. Quote
Lethaface Posted March 4, 2007 Author Report Posted March 4, 2007 (edited) bansheeseat, It could be gasket thickness making the extra compression.. Thanks handyman! Thanks Dave, I guess i just better get it all together and keep a close eye on the compression during break in.. Edited March 4, 2007 by Lethaface Quote
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