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Yamaha MX & Off-Road Dirt Bikes
Advice on Octane Boost for 2002 Yamaha WR250F
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[QUOTE="Rich Rohrich, post: 488234, member: 16241"] [b]NO[/b] if you are talking about pump fuel. Here's some of my [b]personal[/b] basic rules of thumb: - ALL US pump fuel is [b]TOTAL crap[/b] for use in a modern race bike. The degree of [b]crappiness[/b] varies based on a ton of factors and vary from week to week so you'll never consistently pin them down . - Premium pump fuel from big name companies tends to be less crappy than the cheaper low octane stuff, so using low grade pump fuel is ASSININE IMHO. - Pump fuels that use ethanol (alcohol) as their oxygenating agent will cause the most problems in terms of jetting, water absorption, and corrosion. Ethanol doped fuels have no business in a modern race bike. - MTBE is [b]not[/b] some chemical anti-chris[i][/i]t that needs to be avoided. Regardless of what the local nit wit mechanic or knee jerk, failed out of all his science classes, clueless green freak might want to tell you. - In almost every case 100ll Avgas is a better choice than current US alcohol based pump fuels - Mixing 100LL Avgas with a good race gas designed for your application and rpm range is a reasonable way to save some money, and makes more sense then dumping crappy pump fuel into good race fuel. - Mixing alcohol based pump fuels with ANYTHING in an attempt to make it BETTER is just a chemical circle jerk, and if you're that cheap or that ignorant you deserve the crummy performance and the insurmountable jetting problems that you will invariably be blessed with. Here's some additional info on MTBE for those of you who have dozed off YET :confused: AMA legal race fuels with MTBE generally contain about 15% by volume and subsequently have a lower energy per pound. You have to look at the big picture to see how this works in our favor. Here's a few numbers to explain things : Typical leaded race fuel (no oxygenates) = 18636 (BTU/lb) Typical unleaded race fuel (with ~15% MTBE by vol) = 17876 (BTU/lb) MTBE = 16353 (BTU/lb) As you can see the addition of MTBE lowers the overall energy value. So on the surface it looks like the leaded race fuel with highery energy content would make more power. But we know it doesn't. HOW COME? We have to look a little deeper and figure out the heat available in the cylinder per pound of air. If we look at the chemically correct (Stoichiometric Ratio) air/fuel ratio of our non-MTBE fuel we see it's 14.88 while the MTBE laced fuel has a Stoichiometric Ratio of 14.15 (for reference MTBE is 11.76) . So that tells us we need to add more fuel for each pound of air we ingest into the cylinder when we are using an MTBE based fuel. In this particualr example we would need to add 1.016 times more fuel with the MTBE based fuel (1.228 for pure MTBE). So we have more fuel in the cylinder for each pound of air with our oxygenated fuel and the actual heat available in the cylinder per pound of air (or specific energy)looks like this: Typical unleaded race fuel (~15% MTBE by vol) = 1263 BTU/lb of air Typical leaded race fuel (no oxygenates) = 1252 BTU/lb of air MTBE = 1391 BTU/lb of air So as you can see even though the non-oxygenated fuel started with an advantage sitting in our fuel can once it got around to doing some real work it loses the race. The super-fuels Nitromethane and Methanol have similar characteristics to our MTBE-fuel. Lower energy per pound but higher specific energy when you add in enough fuel to compensate for their lower stoichiometric ratios ( about 6.47 for Methanol and about 2.1 for Nitromethane). All that extra fuel adds up to lots of extra oomph. In short, if you want to run pump fuel you are going to trade off some performance and response [b]PERIOD[/b]. Whether or not that trade off is an issue is up to you decide. [/QUOTE]
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Yamaha MX & Off-Road Dirt Bikes
Advice on Octane Boost for 2002 Yamaha WR250F
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