with an 11.5:1 piston and cam. what can i expect with higher than 93 octane gas. any damage? what brand? what octane? power increase?

 

Just run pump gas. C12 or other fuels will be a waste of money.

 

Just buy AV gas (aviation fuel) you can get it at any airport. it's 100+ octane and posibly better and cleaner then race gas. It's way cheaper then race gas also by more than a dollar! Just go there with your 5 gallon can and ask them to fill it up.

-Darren

 

AV gas is NOT the "way to go." AV gas has a different specific gravity and is made for a different purpose. Perhaps the older AV gas that was high lead may have been ok for the budget racer; however, today's lead free and low lead AV gas is not something you will need.

The main reason why you would need "fuel" is because you have a pinging problem. Depending on your cam specs, stroke and head design, you may not need to go beyond pump gas. Don't think fuel is the end all instant performance booster... it is not.

 

Here is some info on AV-gas from a PWC Racing Vendor.....They have alot of good 2-stroke PWC information that can be helpful understanding any type of motor.

www.groupk.com/tec-gas96.htm

"ABOUT AVIATION FUELS - Aviation gasoline (or "av gas&quot is blended specifically for use in small aircraft. It's also commonly used by many high performance engine owners because of it's high stated octane rating (usually 100-110) and the relatively low price compared to racing fuel. Unfortunately this fuel is not all it appears to be. Avgas octane is rated on a different scale than gasoline's intended for ground level use. What is 100 octane "av", is not necessarily 100 octane "ground level". Besides this, there is also a big chemical difference. Normal ground level race fuels are made up of gas molecules that have a "light end" and a "heavy end". The light end of the molecule ignites easily and burns quickly with a low temperature flame (as a piece of thin newspaper would burn). The heavy end of the molecule is not so easily ignited, but it burns with a much more intense heat (as an oak log would). This heavy end of the gasoline molecule is responsible for the hotter, more powerful part of the combustion process.

Small aircraft are constructed as very weight conscious vehicles. That's because their somewhat weak engines often have difficulty taking off with any extra weight. To help reduce this weight problem, aviation gasoline's are blended with no heavy molecule end. This makes a gallon of avgas weigh substantially less than a gallon of ground level fuel. Since small plane engines turn very low rpms and produce so little power, the omission of the heavy end is not a horsepower issue. However, for high output pwc racing engines, there is defiantly a compromise in power. This, despite the fact that many pwc owners experience the desirable cooler operating temperatures that avgas offers. In addition, some blends of avgas will quickly separate from some oils used in premix situations. For the above reasons, we do not recommend the ongoing use of 100% avgas, and we will not prepare any "avgas" engine kits.

Despite all this bad news, running avgas (accepting the slight power loss) is usually a better choice than burning down a high output engine on regular pump gas. In this situation, the best choice is usually a 50/50 mix of pump and avgas. That provides "some" heavy molecule ends for the engine."

 

Raptor720 is right. For years, racing mags have issued tech info that clearly shows that higher-octane pump fuels have no more inherent explosive energy than regular pump gas. They simply control the pre-ignition factor better. Therefore, use the lowest octane pump gas that doesn't knock under full-load acceleration. Racing fuel is only necessary for race engines, since they have extremely high compression ratios and race cams that would cause harmful pinging without the extra octane.

But trying to convince a 20 year old of this fact, when he uses race gas in his stock atv, is probably a waste of time.

ps: most modern car/truck engines have anti-knock sensors that allow the computer to advance the timing so as to get max power out of the fuel you use. Therefore, higher octane pump fuels will produce more hp than regular pump gas. But atvs have no such sensors.

 

Very true...if it doesn't knock it doesn't need better fuel.

FYI...A human ear can't always detect a borderline knock. Engines produce the most power out of a given fuel at this boarderline point. But it also reduces the engines life.

Best bet is to see if you can hear any knock at a low RPM under heavy load and then upgrade or downgrade your fuel accordingly.

The raptor doesn't have a very aggressive stock timing advance or compression ratio...so pump gas is fine.

Also in modern cars the Knock Sensor only retards the timing (and maybe increase the fuel mixture) when knocking is detected, it does not advance the timing until a knock occurs. Using a higher octane fuel does not increase power unless the computer is modified (more aggressive advance and better fuel mixture) and/or the compression ratio is increased.

But Go ahead and spend your money on the premium....as long as you buy it from one of our C-stores or Supermarket Fuel Centers....the extra profit helps increase my bonus so I can buy new parts for my Raptor.

 

Thanks for the support guys,

I am usually here defending my positions. [img]i/expressions/face-icon-small-smile.gif[/img]