superfastyfz450driver Posted March 31, 2010 Report Share Posted March 31, 2010 hi every one what size domes do you all suggest for a 4mmstroker, 68mm bore cub running on methanol, using 36mm carbs, and cpi inframes, running 1/4 - 1/2 mile oval tracks right now i have 17cc domes, but i have all the facilities and equipment to open them up a bit if i need be Quote Link to comment Share on other sites More sharing options...
firebanshee Posted March 31, 2010 Report Share Posted March 31, 2010 I liked my 21cc domes, good torque and good over-rev. Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted March 31, 2010 Report Share Posted March 31, 2010 first what kind of compression do you have now with the 17's? high i would assume Quote Link to comment Share on other sites More sharing options...
Wheelman Chassis Posted March 31, 2010 Report Share Posted March 31, 2010 i have redline alky domes ,they are 19cc's and im at sea levelish. my 4mm cubpumps like 165-170lbs..runs like a raped ape. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted March 31, 2010 Report Share Posted March 31, 2010 Depending on number of laps,you will find you wanna stay on the low side with the compression if your in it for long periods,also think about running just a lil timing advance,but im no exprt on roundy-round Quote Link to comment Share on other sites More sharing options...
superfastyfz450driver Posted March 31, 2010 Author Report Share Posted March 31, 2010 im going to do a compression test tonight and i will let you guys know, and also yes i will be running between sea level and 500 feet above Quote Link to comment Share on other sites More sharing options...
superfastyfz450driver Posted April 1, 2010 Author Report Share Posted April 1, 2010 ok here is the results from the compression test 162 on the mag side and 160 on the pto side, squish is .075'', Quote Link to comment Share on other sites More sharing options...
alcoholbanshee Posted April 1, 2010 Report Share Posted April 1, 2010 ok here is the results from the compression test 162 on the mag side and 160 on the pto side, squish is .075'', Squish is to loose. I would like to see it at around .045 to .055. With 17cc domes you should have way more compression than that. The thing prolly runs like poo right now huh....... If I had to guess I would say you have to thick of a base gasket on right now. I dont remember anymore but I think the 421's are supposed to have a real thin base gasket like .012 or something like that. Quote Link to comment Share on other sites More sharing options...
superfastyfz450driver Posted April 2, 2010 Author Report Share Posted April 2, 2010 i havent had the bike running yet, by the weekend i should be able to drive it around i hope, but right now my main concerns are to have a bike that will also hold together for up to 15 laps also Quote Link to comment Share on other sites More sharing options...
banshee332 Posted April 2, 2010 Report Share Posted April 2, 2010 i havent had the bike running yet, by the weekend i should be able to drive it around i hope, but right now my main concerns are to have a bike that will also hold together for up to 15 laps also So if you never had it running the rings have not had time to seat. I would guess once you break it in you should have more compression. Guess thats how it works,but Like Roger said the squish is to lose. I like it around 52-55 Quote Link to comment Share on other sites More sharing options...
sheefreak Posted April 2, 2010 Report Share Posted April 2, 2010 The rings seating won't make that big of a difference. Bringing that squish down to where it should be definately will. Quote Link to comment Share on other sites More sharing options...
superfastyfz450driver Posted April 2, 2010 Author Report Share Posted April 2, 2010 what is the minimum amount of compression for alcohol, like i said i would rather play it a little on the safe side and work my way up then the other way around especially on a nicasil cylinder, if it was cast iron lined and i had to over bore wouldnt be such a big deal Quote Link to comment Share on other sites More sharing options...
J-Madd Posted April 2, 2010 Report Share Posted April 2, 2010 I have a friend with a 397 Cub that kicks 105 psi. His compression ratio is probably ridiculous, though. It's the fastest 0-400 cc Banshee that I have ever saw run in 300 ft. A tenth faster than the current "record." Anyway, as mentioned - check the thickness of that base gasket; should probably be 0.012". Get that squish down a little. You may need it a little looser than us drag racers; but not that loose. You can probably get by with lower compression and timing also. You'll create too much heat with high compression and timing racing that oval, imo. Quote Link to comment Share on other sites More sharing options...
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