killshee Posted November 28, 2008 Report Posted November 28, 2008 wanted to kno if anyone can tell me how high in compression u can go b4 u have to change to race fuel??? Quote
Misssppelllleddd Posted November 28, 2008 Report Posted November 28, 2008 well....i want to say about 160 is where you would want to change to race fuel....at 180-190 lbs of compression i ran 110. 195lbs is pushing it for 110. elevation will also change your compression.... Quote
crazycanuck Posted November 28, 2008 Report Posted November 28, 2008 think anything higher than 150lbs will need race fuel, do u know what urs are?? Quote
278 Posted November 28, 2008 Report Posted November 28, 2008 Id say it depends on your riding. What I mean is if you ride in the same place all the time and your comp. is at 155 there youll be ok, but if your altitude changes up and down from where you did your comp test and its 155 then I would run 100 octane. About 155 is where you need to start considering it. If you get to 160 I'd run 100, 165 Id consider going 110, 170-175 Id run 112-115, and you'll probably be in there somewhere if your higher than 175 or 180 then you need to go higher and Id talk to your builder and see what he suggests Quote
RIPPEN Posted November 28, 2008 Report Posted November 28, 2008 Once you hit around 160 Id be going to the safe side and runnin 50/50... 170-175 or so I would go straight race fuel.. Thats what I have always done anyway.. RIPPEN Quote
dajogejr Posted November 28, 2008 Report Posted November 28, 2008 Compression ratio, NOT cranking compression dictates the need for more/less octane. If the motor is on stock porting...and you're sure of this, make it easy. Over 160PSI, run straight race fuel, under, run 92 or 93 octane. You're going to hear guys that say they have 180 to 200 PSI and run pump gas, guys that have 140PSI and swear they need race fuel.... The only sure way is to measure the compression ratio, that is how fuel is measured to be knock-resistant. Big advances in timing require more octane, but compression is more needy than timing.... Quote
deckheight Posted November 30, 2008 Report Posted November 30, 2008 Sound advise there folks! There is no professional motorsport in the world that uses a compression gauge to establish fuel octane requirements, that I am aware of anyway. Compression ratio, NOT cranking compression dictates the need for more/less octane. The only sure way is to measure the compression ratio, that is how fuel is measured to be knock-resistant. Big advances in timing require more octane, but compression is more needy than timing.... Quote
RIPPEN Posted November 30, 2008 Report Posted November 30, 2008 Sound advise there folks! There is no professional motorsport in the world that uses a compression gauge to establish fuel octane requirements, that I am aware of anyway. Well there isn't anyone on here that Iam aware of that is profesionaly competing in motorsports.. lol Serioulsy though.. I agree 100% with Dave that going solely off cranking compression isn't the BEST way to figure out fuel requirements as there are different variables in everyones set-up.. However taking accurate measurment of cranking compression and roughly factoring in the other variables such as timing and such atleast helps to give you a baseline.. When It comes to fuel I always try to "play it a little safe" anyway, atleast that way you maybe hurting a tad in performance rather than sevearly physicly hurting componets.. Like I said, I understand cranking comp isn't as accurate as figuring it out the "long way" but is a bit more practical and straight forward for allot of guys(including myself).. :biggrin: RIPPEN Quote
deckheight Posted December 1, 2008 Report Posted December 1, 2008 Sounds like were both on the same page :biggrin: :biggrin: Wether it is the "long way" or not might depend on an individuals ability to pay for parts and labor. LOL! I understand your point as far as static compression readings being understandable however. With "Accurate" being a somewhat relative term anyway... :ermm: Quote
Misssppelllleddd Posted December 1, 2008 Report Posted December 1, 2008 Compression ratio, NOT cranking compression dictates the need for more/less octane. If the motor is on stock porting...and you're sure of this, make it easy. Over 160PSI, run straight race fuel, under, run 92 or 93 octane. You're going to hear guys that say they have 180 to 200 PSI and run pump gas, guys that have 140PSI and swear they need race fuel.... The only sure way is to measure the compression ratio, that is how fuel is measured to be knock-resistant. Big advances in timing require more octane, but compression is more needy than timing.... I learn something new everyday from this site. :thumbsup: Quote
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