Does it make a difference?
May 21, 2004 | 12:58 AM
#11
Pro Rider
Joined: Feb 2004
Posts: 612
Likes: 1
Does it make a difference?
you only need to run high octane gas in machine with high compression. Octane is the resistance to burn, higher compresion engine will detionate with lower octane gas because the fuel mixture will ignition before the spark plug fires. This runs hotter and burn holes through pistons. So you shouldn't notice any power difference
May 21, 2004 | 05:47 PM
#12
Air Cooled Rider
Future Govenator of Kalifornia!
Future Govenator of Kalifornia!
Joined: Feb 2003
Posts: 17,419
Likes: 0
From: Clovis, CA
Does it make a difference?
The whole octane thing has been gone over before on the site. Search around for it. I've seen links to other sites with more info.
Only go up in octane when you up your compression. Otherwise, run what the manufacturer suggests. Make sure the octane rating is what the manufacturer is basing on. There is MON, RON and a Road Octane which I believe is what you see on the pumps now. It's an average of RON & MON.) The lower octane fuels burn faster. So you will get more HP with a lower fuel octane. This goes against "common knowledge" that just changing the fuel will gain you more HP. It won't. Until you go into your motor (increasing compression) or add turbo or supercharging you don't need more octane. Using an inreadibly high octane fuel, unless the engine needs it, can actually make it run slower. The additives (usually 2 different forms of lead) used to slow the flame front can actually slow it down too much.
Also note that each engine coupled with it's operating environment have different requirements. So, in the middle of winter with cold intake temps and cold cooling air the motor will run cooler and need a lower octane. Same bike, but this time you've decided to head to Glamis in the middle of summer and it's 120F outside. Well, your octane requirement just went up.
On a 4-stroke bike, mearly doing porting, pollishing, intake and exhaust mods shouldn't effect the octane requirement. From what I read, jetting could possibly change it. You'll need to actually change the compression ratio of the motor to increase your octane requirement.
Now, that said, doing port work on a 2-stroke could change the requirement. Especially if you are raising the exhaust ports. You would think this would lower the compression, but it actually raises it because of the way the 2-stroke works by pulling some charge back in from the exhaust.
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Only go up in octane when you up your compression. Otherwise, run what the manufacturer suggests. Make sure the octane rating is what the manufacturer is basing on. There is MON, RON and a Road Octane which I believe is what you see on the pumps now. It's an average of RON & MON.) The lower octane fuels burn faster. So you will get more HP with a lower fuel octane. This goes against "common knowledge" that just changing the fuel will gain you more HP. It won't. Until you go into your motor (increasing compression) or add turbo or supercharging you don't need more octane. Using an inreadibly high octane fuel, unless the engine needs it, can actually make it run slower. The additives (usually 2 different forms of lead) used to slow the flame front can actually slow it down too much.
Also note that each engine coupled with it's operating environment have different requirements. So, in the middle of winter with cold intake temps and cold cooling air the motor will run cooler and need a lower octane. Same bike, but this time you've decided to head to Glamis in the middle of summer and it's 120F outside. Well, your octane requirement just went up.
On a 4-stroke bike, mearly doing porting, pollishing, intake and exhaust mods shouldn't effect the octane requirement. From what I read, jetting could possibly change it. You'll need to actually change the compression ratio of the motor to increase your octane requirement.
Now, that said, doing port work on a 2-stroke could change the requirement. Especially if you are raising the exhaust ports. You would think this would lower the compression, but it actually raises it because of the way the 2-stroke works by pulling some charge back in from the exhaust.
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