What Octane?

[AtvKid4Eva]

I have an 02 400ex the motor is all stock and it has a HMF slip on. I was wondering what the best octane gas to run would be thanks.

[nowukno]

I would run mid grade 89 or 91 , or pay a little extra and run premium.

[400exrider26]

For a stock 400ex it says right in the manuel to run 92 octane or above... So premium would be your best bet.

[Elyk]

I run 87 in my stock 05 ex and it runs just fine.

[AtvKid4Eva]

yea i run 87 and it runs fine i was jw if i ran a higher grade if it would run any better?

[xsr71x]

Originally posted by 400exrider26
For a stock 400ex it says right in the manuel to run 92 octane or above... So premium would be your best bet.

Look closer at the manual and how they figue that number you might be suprised!

[xsr71x]

Originally posted by AtvKid4Eva
yea i run 87 and it runs fine i was jw if i ran a higher grade if it would run any better?

Nope.. octane prevents pre-detonation, if you are getting symptoms of such you should add octane, but unless you are running oxygenated race gas the lower the octane the better. If you run octane higher than needed by the engine you have more carbon deposits on valves piston etc.

[underpowered]

Originally posted by xsr71x
Nope.. octane prevents pre-detonation, if you are getting symptoms of such you should add octane, but unless you are running oxygenated race gas the lower the octane the better. If you run octane higher than needed by the engine you have more carbon deposits on valves piston etc.

close, but teh higher octane fuels burn cleaner and therefore less carbon buildup.

[xsr71x]

Check your facts.. The closer you are to perfect octane the less buildup... search the web someone did some cool head to head tests.

[underpowered]

Originally posted by xsr71x
Check your facts.. The closer you are to perfect octane the less buildup... search the web someone did some cool head to head tests.

this i know, but the motor was built to run on 92+ octane fuel, check your facts. So running 87 will cause detonation when the motor is lugging or hot. i run 93 in mine with 11:1 comp. 426. i also run race fuel even though i do not have to because teh octane varies greatly in pump gas. a quality fuel will burn cleaner and more efficiently than pump fuel. Most people seem to think that a black exhaust tip is a tipoff to a rich fuel mixture when in reality your jetting may be perfect but the poor quality and additives in todays fuels cause the black buildup on the tip.

[Rip_Tear]

I wasn't going to post but... Don't forget the pump is telling you the "minium" octane that you are getting, a 87 pump could be giving you 90ish or more even, could be less, but no less then 87. The lower your octane the cooler your engine runs, so I would just test your atv(or any motor) out with different stuff, you can't really hurt it running more or less.

[underpowered]

Originally posted by Rip_Tear
The lower your octane the cooler your engine runs, so I would just test your atv(or any motor) out with different stuff, you can't really hurt it running more or less.

not really, the Higher the octane teh cooler it will run. higher octane resist detonation so it will burn when it is supposed to burn. race fuel will run cooler than pump gas in the same engine.

[ridred4eva01]

if you run too high of octane you'll actually loose horsepower it's dyno proven

[xsr71x]

Originally posted by ridred4eva01
if you run too high of octane you'll actually loose horsepower it's dyno proven
Dern and to think I didn't know what I was talking about..:rolleyes: