HELP: Question about Octane/fuel.....kinda long sorry

[mtn_rider]

I was told recently by one of the guys at the local doo shop that I should consider using more than 91 octane in my 03 Summit 800. He suggested that I get model airplane fuel and mix 2 oz of that with every gallon of fuel I ran in the sled. He said this misture would raise the fuel to about 100 octane. I have never had any problems with running normal 91 octane, but I figured I might as well give it a shot. Instead of going to full out 100 octane, I bought 93 octance from the gas station and added an octane boosting compound. I crunched the numbers and I am pretty sure that the last tank of gas I ran through the engine was 96 octane. Now call me crazy, but I started the sled and as soon as it burned through the remaining 91 octane in the fuel line and starting sucking in the 96 octane, the idle rpms went down considerably(almost 400 rpms). I guess this makes sense since the higher the octane, the slower the fuel burns??? (I am not sure about that, I never paid attention in my petrol engineering class.) So i got out the next day in some deep snow and rallied around for about half an hour. The sled ran phenominally well!!! I was stoked, but then I got to wondering about the jetting and all the other stuff that the higher octance could potentially mess with. I am rather ignorant about snomobile engines, so I was wondering if you sled goo-roos could help me out with these questions.

1. Are there long/short term harmful consequences to running above 91 octane without adjusting anything?

2. Am I on crack or would the higher octane really make the engine idle lower and run better?

3. Should I stick with 91 octance or am I safe to play around with the fuel mixture

4. Is the model airplane fuel the best way to raise octane or should I continue to use regular octane booster.

Any help you all could give me in this would be greatly appreciated!!
Thanks

 

[winter brew]

If you have been fine with 91 all these years there is no reason to run more octane. Higher octane is more resistant to detonation....but if you have no detonation then the only thing additional octane will do is LOSE hp....probably 3-4 peak HP. Unless you go with more compression or more timing there is no need for it. Also, not sure exactly what additive you are using but alcohol based fuel can attract moisture and be harmful to fuel pump/lines if they are not designed for alcohol....Like the Doo reed cages.

 

[slyrydr]

unless you are running higher than stock compression due to an aftermarket head or shaved head, high octane will not give you more power and as wb said will lose you power due to the slower burn and the less energy in high octane fuels as compared to pump gas...and the additives in some of the "fuels" are definitely more corrosive to fuel lines, seals, and components...don't mean to knock whoever told you that the high octane was better, but it isn't so....

 

[mtn_rider]

thanks

thanks alot for the advice. I am not supremely thrilled with the advice I have been getting at this shop, but the answers i get from on SW for you all have always panned out. I really appreciate the honest advice. No more high test octane for me.

 

[DWHalverson]

Run it the way you have been. The off the shelf octane boosters are snake oil at best. There are some things you could mix to bump the octane up about 2.5 MON points, but that is with a 20-30% mix. The nitromethane you used probably has a higher specific gravity rating that should/might require a leaner jetting combo if enough was used. As was stated above, too much octane for the required application and you are loosing power.

 

[Jaynelson]

Won't do anything except negatively affect your hp and bank account. Best power levels come from running the least amount of octane needed to avoid detonation...plus some safety margin, of course, of which 91 has plenty if your sled is near-stock.

No "octane boost" you could have bought jumped your octane from 93 to 96, unforunately that stuff is marketed mostly for people who never needed more octane points in the first place...