just want some opinions on running hi octane gas when it's not needed. Does it give you more power? Example. Lets say you had 2 brand new identical 400EX's. You have 93 ocatane in one and leaded 110 octane in the other. Will the bike with the 110 be faster? I thought I knew the answer to this but I've seen a few things lately that really have me wondering.

Nope, there is no benefit to running that high of octane in that situation. On a stock 400ex you don't really even need to run 93 octane.

stock compression on a 400ex at i think it was 8.5:1 high octane gas would offer no real gains. with hogher compression comes the need for hotter gas. the 450r is 11:1 and 93 octane is pretty much right on for it. higher compressions need higher octanes to work correctly and produce more power

The stockcompression on a 450R is 10.5:1. I have read on this forms in several threads that running 110 octane when not neededcan actually make your bike run slower.

Use oxygenated fuel if you want more power from your fuel

Its not the high octane fuel that provides more power, it is the engine components used that require high octane fuel that produces more power. If the components do not need race fuel than there is no advantage of using it. Race gas will lighten your pocket some if you need to shave some weight off for faster acceleration .

Leaded fuel is better for all engines but harsh on the enviroment and is probably what people confuse for high octane sometimes.

Get it, got it, good :D

actually, in the scenario you describe the one running on 110 would be slower

Thanks guys, thats pretty much exactly what I thought. Weird thing happened to me though. Me and my buddy both have 450R's both have cams and exhaust and jetting. He weighs about 50 pounds more than me so when we race I always beat him. We always run 93 octane. He filled up with 110 leaded and now he beats me! We are going to put 110 in both of them and see what happens!

that should be interesting!

well I think mabe he used oxygenated fuel.

High octane and high compression goes together. Low compression needs lower octane and high compression needs high octane to stop detonation. High octane burns slower. If you have too much octane for compression, may hurt more than helping.

Correct me if I'm wrong, but the higher octane burns cooler, to reduce predetionation, lower octane burns hotter. Hypethetically, you'd get the most power from running the lowest octaine possible, without detionating. Right?

Im running a 50/50 mix of VP110 and pump gas ,you do notice the diff(a little) and the price of pump these days isnt much more than the 110,,i think i really run it for the smell alone ,,,OOO OOO that smell ,,,the pump out here is 3.60 a gal and the VP is 4.11 a gal and with the 50/50 mix the VP lasts a long time

I don't know if I want to get into this but, here we go. While 1BAD was close with his description, his wording was off slightly. Excellent shot though.

Predetonation is not really a word. Pre-ignition and detonation are some things that can happen from poor fuel though. Pre-ignition is the fuel lighting off on it's own from somewhere inside the combustion chamber other than from the spark plug and obviously an unwanted scenario. This would be the same as jacking the timing around so it fires, oh, say 15-25 degrees before it is supposed to. This is usually caused by some hot spot in the combustion chamber, really low octane fuel, or just plain poor fuel. It can also sometimes be caused by lean jetting when the machine is working really hard but, this scenario lends itself more to detonation, it's a really fine line there.

Detonation is the explosion of fuel when an engine is being worked at it's maximum capacity over a long enough period of time to completely vaporize the incoming charge and then compress it enough that it explodes under the pressure of being squeezed instead of ignited by the plug and then burned in a controlled fashion. (that was a really long sentence, sorry) Too low of octane fuel will do this simply because the bond between the molecule chains aren't strong enough and the fuel vaporizes too easily. This is also the reason I don't like mixxing fuels, the molecular bonds in these chains can be broken apart by different compounds in the differing fuel types. Like mixxing pump gas and race fuel, just plain not a good idea.

The two things you should realize about detonation and pre-ignition, pre-ignition will really raise the operating temps of the motor quickly since the engine is fighting itself to run. Detonation is just self contained violence. It happens so quickly and is over so fast that unless it does permanent damage (most likely the case) you'll never know it happened until you tear the motor apart because it suddenly has become slow running. Stuck rings, bent rods, broken rods, broken piston tops, broken piston skirts, all can be the results of detonation. The giveaway is "spots" of carbon missing from the piston top or cylinder head. Pre-ignition is just that, the fuel is still burning, not exploding. With pre-ignition it is more likely to melt the dome of the piston away, most times just to the exhaust side of the spark plug tip.

When diagnosing a piston failure it's important to look at the evidence carefully. If it has a hole melted in it and also signs of detonation, what would be the actual cause? Pre-ignition! Why? Because as the piston dome melts away it spreads the metal around on the dome and as the engine fights to run it gets these particles hot and starts lighting the fuel off in different locations, in effect, causing detonation when the flame fronts colide.

I know I have explained this before a couple times on this forum, maybe we can pin this?

Sorry about that 1BAD, don't mean to step on your toes. :blush: Welcome to the site.

Tony

So it is writen, so it shall be done. (Bonus points for anyone under 25 that can name that movie.)


I'll leave this thread here for a while, and then I'll put it in the Engine Tech FAQ. Nice job Tony

Tony, that's kinda what I was getting at. Thanks for clearing it up! :D

if u have a high compression engine as the 450r u must run high octane if you dont youll have pre-ignition.low octane will basically turn a high compression engine into a diesel engine.{diesels fire because of the compression, thats why there in the neighborhood of 20 to 1 compression ratio} in other words the fuel is being burned before top dead center. its firing off the fuel as soon as the fuel charge is compressed enough.
so to fix this you run high octane the more octane the more it can be compressed, therfore the high compression engine can fire the fuel when it is suppossed too

Yule Brenner in Charleton Heston's Moses. I think.

I'm only tree and a half yeas ooold.

Tony

Big Daddy?

JESUS????? :D

WELL i agree 100% with tony ticemans post...

so in theory the reason a lower compression bike will run worse on leaded 111 for example isnt because the gas is bad or something it just takes more energy to light it during the ignition stage of the engine...so therefore an engine that normally ignites a spark bEFORE TOP DEAD CENTER...in reality isnt actually firing the mix until after TDC and that is not optimal for power and therfore will loose some effiecency in flame travel and power cause the mixture wont have its optimal dynamic compression at ignition...and the fuel which opperates much more stable under compression will not burn as well as a lower octane/pump fuel would burn...

race gas dont make more power ( unless oxygenated) it just lets a high compression motor run the way it should and keeps things under control for clean burn on every stroke regardless of engine heat due to harsh conditions like racing...

when i ran a 13-1 compression piston in my yfz on pump gas it was most noticeable climbing long hills in 3rd gear...the piston i assume would get hot (obviously under hot condtions dragging my big butt up a hill at over 9K...in turn i would loose rpms and power once the engine got hotter....enter the high octane leaded gas and vioualla (misspelled :D ) the bike would actually rev the way it should (better) and wouldnt loose power by the top of the large hills...it just ran far cleaner than the 91...was i burning more fuel??? nope...but my bike felt like it was burning cleaner and there was no chance for preburn with the more stable octanes....

also correct me if im wrong guys but i believe lead in gasoline offers a cooling affect...BUT i could be way off on that one...i know alky runs super cool

but the reason all our race gases come with lead is because lead makes OCTANE...and octane fights the preburns or preignitions or detonations however you want to label each condition that hurts power and even reliability...

pump gasses these days use many additives to bring up the octanes which are safer then lead but unfortunatley are not necessrily ideal in a high performance engine

later
jason

LOL hope i typed correct info or im about to get schooled by tice