278 Posted December 20, 2008 Report Share Posted December 20, 2008 Ok so I was at the gas station earlier today and I never really payed attention to the octanes, well the supreme gas here is 90 octane WTF? Im pretty sure at 0-500 ft. above sea level, 20cc domes and +4 timing I'm going to need a higher octane fuel... so can you guys give me an estimated compression(since I won't be putting the motor back in the frame for another month so I can't break it in and test it yet), what octane you guys think I should be running, and a good octane booster to use. Quote Link to comment Share on other sites More sharing options...
Bansh-eman Posted December 20, 2008 Report Share Posted December 20, 2008 at around 150 psi i start mixing.... do a comression test and see what your actually kicking. Dont base your motor off what you have read others compressions be at your elevation. Depending on porting, squish, temp, ect the motor can turn completely differant numbers. dont bother with octane boosters. If you need more octane, do it right and buy a differant fuel. Quote Link to comment Share on other sites More sharing options...
GrMeyer Posted December 20, 2008 Report Share Posted December 20, 2008 true. i was thinking i was going to be around 150 psi and kicked out 115 on each and now i need a new top end. but it all looked good when i was in there. but i know what your talking about for oct at the gas stations. when i lived up in wyoming the oct was at 93 and moved to az and its 91. moved out east and it was back to 93 in Ky and Tn. but just moved back to Az and we can get 100 oct at the gas station on unionhills and cavecreek for $8gal. but we started to buy the 5 gal 110 oct and mix it with 5 gal of 91 and it gives you 10 gal of 100 oct. and the oct boosters only are good for like .3 not 3 points. but best of luck and i looked into av gas but it will lead to a early build up of carbon. I always mix in some carb cleaner in my gas. so when ever i take down the carbs they are always very clean on the inside. Quote Link to comment Share on other sites More sharing options...
AKheathen Posted December 20, 2008 Report Share Posted December 20, 2008 i think it was four or five years back that they got rid of the ethanol in alaska, and i immediately bitched up a storm, but what can you do to fight the state? you can get some av gas at merril field. bumped my 700xcsp up to 136 ponnies on the dyno @50/50 Quote Link to comment Share on other sites More sharing options...
deckheight Posted December 20, 2008 Report Share Posted December 20, 2008 Unless you have some other reason to suspect ring sealing problems I would pretty much disregard the low pressure gauge readings. That both cylinders blow the same kinda tells me that everything is good??? 20cc domes on 92 octane doesn't leave much room for error IMHO, so 90 octane is probably not a very good idea, again JMHO. Personally, I would take the octane booster and carb cleaner $$$ and put it toward better fuel or a set of 21cc domes. I've been using 100LL avgas off and on for 20+ years in all types of 2-stroke engines and have never had a problem I could attribute to fuel or noticed any excessive carbon build up or anything else unusual for a leaded fuel. Other than the lead deposits I am kinda at a loss as far as the avgas/carbon connection... Where did you get that info? Last I heard, the FAA doesn't have much of a sense of humor when air planes start falling out of the sky Quote Link to comment Share on other sites More sharing options...
278 Posted December 20, 2008 Author Report Share Posted December 20, 2008 (edited) i think it was four or five years back that they got rid of the ethanol in alaska, and i immediately bitched up a storm, but what can you do to fight the state? you can get some av gas at merril field. bumped my 700xcsp up to 136 ponnies on the dyno @50/50 Yeah now that you mention it I remember hearing about it, but never really payed too much attention. I'll probably start going to ADB and buying trick fuel (as much as I hate to give them anymore business). But yeah I'll just do a check when I get it together I just wanted some other opinions on the whole octane thing. Im pretty sure Ill have to run race fuel, how much of a power gain will I see from running my 20cc domes and running 100-106 octane fuel instead of 21 or 22 cc domes and 90 octane fuel Edited December 20, 2008 by 278 Quote Link to comment Share on other sites More sharing options...
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