Racing Fuel?

[northern bear]

I want to put a high compression piston in my ride. At what point does a person need to start running race gas, and what blend do u need respectively for different compression ratios? Thinking around a 12:1 ratio. Also if i went 50/50 blend on the fuel would it hurt a stock engine?

[DaveB]

Depends on the cam. A big cam with lots of overlap will bleed off compression at low RPMs and let you run lower octane fuel. But...just thinking in averages....your stock piston is what, 9.5 to 10:1 and is recommended to run on regular...? You could probably run 91 premium with a 11:1 and even 12:1 with premium at elevation. For low elevation running a mix is safe.

I'm cheap....I never buy race gas. I run my hi-comp stuff on a mix of 91 premium and AV gas (LL100). Most small local airports will fill approved containers with LL100 and it only costs a little more per litre than premium. I run 50/50 AV gas/premium in my 14:1 sled motors (2 stroke).

Running MORE race fuel or AV gas than you need won't physically hurt the motor if it doesn't need it.....but it will make LESS HP than it would with the correct lower octane mix. I guess what I would do is start with lots of high octane, run it, then start running less and less until you get it to get it to knock at low rpm when you lug it. You may find out that it will be fine with straight 91 premium.

Of course...the easiest way is to wait until a fellow Grizz guy who has done this jumps in and tells us what works...LOL.

[imdoo'n]

i've tried to get av gas at the RD airport, only they are not interested in filling a 5 gallon jerry can. you say approved can is that one of the red cans?

[DaveB]

I go to Skywings out there all the time and fill 4 or 5 red jerry cans....no issues.

[northern bear]

Thanks Daveb, makes sense. Probably gonna run about 12:1 with a mudbuster cam (stage one hotcam). I noticed a significant gain right now running 91 vs 87 just by adding the pipe. no difference before. gonna try a 50/50 blend this weekend see how it works. worst case scenario them kawi's i ride with will still beat me in a drag

[imdoo'n]

i didn't have the need for that much, at the time, but did get some fuel that they had drained from one of the planes that had landed. used it in a dirt bike for ice races. will have to go there again maybe pick up a few jerry cans full

[BIG_BRUTE750]

Originally Posted by northern bear

Thanks Daveb, makes sense. Probably gonna run about 12:1 with a mudbuster cam (stage one hotcam). I noticed a significant gain right now running 91 vs 87 just by adding the pipe. no difference before. gonna try a 50/50 blend this weekend see how it works. worst case scenario them kawi's i ride with will still beat me in a drag

LOL!!!!