Don't hang me, but I have an Octane question

B

Bigger Hammer

New member
Joined
Oct 27, 2005
Messages
14
Age
44
Location
Michigan
OK, I am mainly a 4-stroke guy. Both my dirtbike and main sled are 4 strokers. I have always been under the impression that higher octane dosn't add HP, it is for higher compression engines, so they don't spark knock. Do I have the right basic idea how octane works? I know a guy that rides a Yamaha 250 2-stroke (YZ 250?). He was telling me the other day how he was getting some racing fuel and how much a 2-stroke likes running the high octane gas, and how much more power it adds. As far as I know the bike is stock, except for the exhaust. Do differn't rules apply to 2-stroke powered bikes?

EDIT: Maybe I heard wrong, but I thought he said the race gas he was getting was leaded :dunno:
 
Last edited:

Approach octane the same way you would jetting - too much octane has the same effect as to big of jets - the secret is to find what the engine can use - with todays fuels, 92 pump gas may only be 88 or so - if the motor you are running performs best on 94, a blend of pump gas and race fuel would be in order - I run a 50/50 blend in all of my high performace toys - they perform better and I don't need to concern myself with long term storage issues that you would have with pump gas - I'm sure not everyone will agree, but it works for me!! ;)!
 
Reading the owners manual in my truck, it tunes itself to the fuel used. It will run on 87 but will tune itself for more power (timing advance I think) with better fuel. I think it uses the knock sensors to tune the engine but not sure.

I think you have the right idea. But with racing fuel it will allow leaner jetting and a net higher performance? I know when I was running my turbo cars race gas would allow increased boost pressures. The higher octane cooled the pistons better. It is my understanding that running higher octane than your motor requires will end up in a power loss unless you tune for it?
 
there't additives in race fuel that go well beyond just having high octane. Race fuel will usually make more poower despite being higher octane.
 
I think alot of guys hear the words "race fuel" and they automatically think 110+ octane - I think of race fuel synonymous with "quality fuel" - you can buy 100 octane race fuel mix it with 92 pump and have an awesome 94-96 octane fuel - get the MTBE oxygenated type and it is like a little shot of nitrous!
 
Run too high of octane fuel in a 2 stroke and you will yield low rpm!! Running race fuel doesnt make more power, as someone touched on earlier, you only want just the amount of octane used to supress detonation, anymore then needed doesnt make any more power. If you could theorecticly run a race engine on 87 octane the engine would make the most power, but the octane is needed to supress the detonation from tight squish clearances, high compression, advanced ignition timing, etc. Octane is the fuels ability to "NOT Burn"

If your paticular set up needs 102 octane running 112 will simply result in less power and LESS RPM!! because the higher octane is like corn syrup, it wont burn, you cant even physically start up a sled on a cold day with high octane gas, you need to squirt in some 87 or whatever to get it to start!
 
You could use the LL100 in it, but I would cut that down with 93/94 pumpgas, because the LL100 gas has a additive to keep heat in a plane engine at elevation, but use it like a 60/40 with pump gas would be good 60% 93/94 and 40% LL100.
 
This question goes along w/ this post so could someone tell me the difference between lead additive and octane boost. I am under the impression that lead was added to gas to improve the octane and help lubricate the valves. is this true?
 
You must log in or register to reply here.


Back
Top