Because most race bikes have high enough compression they will detonate on anything less (including 92 octane). The last of the two stroke CR250Rs could NOT run on pump gas. I don't know for sure about the current stock 250 and 450 motocrossers, but I'm betting they may have some detonation problems possibly even with 92 octane and guarantee it if they are built a bit.

In addition some race gas has additives beyond just the octane boost. THAT will increase power, not the higher octane. Fact is if you look at the VP Racing Fuels web site you will find they actually have an 87 octane gas, MR12, that has power boosting additives in the blend - so it isn't the octane.

Many racing organizations including the AMA have octane limiting rules in some classes - an easy way to control the compression level of an engine without getting too technical. Too high of compression - detonation, damages engines. They also may have additive limiting rules too, to stop some trick additives, like a dash of nitro or the like. That is why they take fuel samples from top placing racers at pro levels.

 

Oddly enough most pump gas in the U.S. is usually a blend of both tanks. Kind of like what Sunoco does with their pumps. The variation over the various grades is simply the volume of one fuel over the other. They ran a really low octane 190 for years, their top was 260. No idea what the octanes were.

By the way, I am sure that in both ways to measure octane the function is still the same.

 

Now when you mention actual experience I had the exact opposite experience with my Bultaco Sherpa T trials bike. It ran better with the regular leaded of the day over the high test premium leaded. Seems the bike ran cool enough that the higher octane making the fuel fire at a higher temp caused the T to not burn well at lower rpm in low gears. I always ran regular in it. That was actual "you can truly feel it" experience. Not seat of the pants "I think it runs better", but actual "this damn thing is not firing right" runs worse.

As for your small engines, I'd love to know how you measure it with your mower or a generator.

If there are problems it isn't the octane.

Again VP Racing actually makes an 87 octane high performance fuel that adds up to 5% power proven by their testing.

 

high octane fuel WILL make you faster. it lightens you wallet significantly and the weight savings result in much faster riding.

 

Facts are facts

 

I am in the regular fuel for everything camp. I buy lots of fuel for lots of engines and there is no reason to buy anything more than what the engine was designed for which is regular 87 octane.

Here's an answer to the "smell" issue that some seem to think is an indication of cleanliness... the higher grade gas does not sell well, not many folks buy it for obvious reasons. It's old and the light ends have evaporated off by the time you buy it leaving only stale gas that is not as volatile as it once was. Buying regular fuel assures you a fresher supply. That stink is a good thing, it means that the fuel is converting to gaseous fuel readily. The gasses from gas are what burn.

Ethanol is an entirely different issue. Don't confuse high octane with low ethanol.

 

I've run both 87 and 91 octane in my 09 KLX and to be honest I couldn't tell any difference at all. My bike's engine is basically stock with only jetting and air box lid mods. I think wildcard's comment is hilarious though.

 

Huh, good observation. I wish someone on here had the equipment and chemistry background to maybe test and analyze 87 and 91 for freshness and true octane level (just curious what if it's all a ploy and 91 is actually just 89?!?!?! conspiracy)

 

I'll jump back in here if we're going to discuss the 'moon' landing & '9-11', otherwise I'm out.

 

As hot as it gets in so cal, I'd rather spend the extra money on hi test figuring if it runs cooler the big bore will appreciate it by lasting longer