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Suzuki MX & Off-Road Dirt Bikes
Race gas for RM250
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[QUOTE="Rich Rohrich, post: 803841, member: 16241"] A quote from the link you posted : I love these kinds of sweeping statements from streetbike guys with a dynojet and "all the answers" :rotfl: The reason those fuels can make less horsepower in an RC51 is because the 90% temp, endpoint temp , and pretty much the whole distillation curve in general is wrong for a high speed small combustion chamber engine. They couldn't have picked a more inappropriate group of fuels to run in that engine. Had they bothered to test fuels specifically designed for a high speed four-stroke they would have seen something entirely different. Anyone care to take bets on whether or not they recalibrated the EFI system for every fuel in that test to ensure that the fuel curve was identical in all cases? :rotfl: The idea that any high octane fuel will automatically make less horsepower in an engine like the RC51 is ridiculous. The same can hold true for some pump fuels. The reason that SOME 87 octane fuels can make more power in a high speed four-stroke has to do with the distillation temperatures of the various components. In most cases higher octane components in pump fuel tend to have higher distillation temperatures associated with them. If the distillation temperatures are too high for the application then the fuel can't be properly vaporized in the short time, and short intake tract distance available on a 10,000 rpm four-stroke. You can't burn fuel that you can't vaporize. The same thing holds true on the 250Fs and CRFs. The temperatures at the upper end of the distillation curve on pump fuels are well above 350F, or about 100-200 degrees higher than they should be for our use. This isn't a problem on a closed loop EFI equipped street car with their long very hot intake tracts as they cruise down the highway at 2800 rpm, but it's a big issue for us. Regardless of what you have heard, fuels are very much application specific. The wrong fuel has the same basic effect as the wrong jetting. Two-strokes have a whole different set of requirements than four-strokes, and big bores like the CR500 have different requirements than a tweaked CR125. Bottom line is engines are a system, if you change one thing it impacts the whole system. If you don't choose a fuel that is designed for your application and then jet specifically for that fuel you are just wasting your time and money. If you choose the correct fuel and jet for it you'll find it can be money well spent. [/QUOTE]
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Dirt Bike Discussions By Brand
Suzuki MX & Off-Road Dirt Bikes
Race gas for RM250
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