what is the best octane for performance?about 5 hrs. on bike has 11.7:1 comp.50/50 Sunnoco 110 and 93 r/m unleaded?honda conventional oil for break in.First change 3hrs.
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new 08 honda crf150R octane
- Thread starter mudsling
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The best performance will be from the least amount of octane you can run without getting detonation...If it will run on 87 without detonation you'll get the best performance with that...
There's absolutely no need for 110...More than likely it is slowing the bike down and making it run too rich...
On a 4 stroke motor if you're getting too much fuel it can remove the oil film on the cylinders and dilute the oil...Not a good combination on an engine turning 14,000 rpm.
There's absolutely no need for 110...More than likely it is slowing the bike down and making it run too rich...
On a 4 stroke motor if you're getting too much fuel it can remove the oil film on the cylinders and dilute the oil...Not a good combination on an engine turning 14,000 rpm.
mudsling
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would the lead in the race gas help lube the valves etc.Say about 75% super unleaded and 25% sunnoco 110?Would it make it run cooler?I have a new Dr.D step system and will get the carb rejetted.Thanks
They should be fine on fresh pump premium. Often more power can be found with race gas NOT because of the octane, but because they can use an oxygenate, if jetted for the extra oxygen can make more power just on that. If not jetted they can run leaner which may bring on deto, hopefully the extra octane will ward it off. It's all about testing though. Run er hard on pump premium and inspect the plug with a jewelers magnifier, look for metallic glitter. A few specks is fine, if it's peppered all over it's deto and you want to make some kind of change, either mixture or octane.
Originally Posted By: CaspianM
Can you explain how octane can change the af ratio? I would like to know.
Well, octane won't.
But in a carburated engine, the engine produces vacuum that pulls the fuel through the jets.
As the specific gravity of a fuel changes, so will the amount of fuel that gets into the cylinder. So, everything being equal, pump gas has a specific gravity around .755. Most 110 leaded racing fuels are in the .710 to .730 area. If one just changed the fuel, it would be richer as more fuel would be pulled into the combustion chamber.
Oxygenated fuels are available. A lot of pump gas has oxygenates too from ethanol to MTBE. The addition of those additives further leans out AF mixtures.
A common 110 leaded is NOT oxygenated. Some unleaded racing fuels that are easily available have some oxygenate at times.
Lead is available in some fuels. Really, the aromatics and the lead in those fuels can be a benefit when added to pump gas in that 75% pump gas/25% race fuel. Unleaded fuels burn a bit scattered, but when lead is introduced, it usually will contribute to a more uniform flame burn. That can lean out the mixture a little as the AF in the combustion chamber is burned more so than just an unleaded.
Given that one's jetting is "correct", I'd start by cutting the pump gas with a little 110 leaded fuel. The overall mixture will end up having a little lighter specific gravity, have a little lead, and have a little more of the aromatic chemicals that have been pulled out of fuel. It should allow for a little better burn in the cylinder without changing jetting.
Hope that gives you some ideas.
Can you explain how octane can change the af ratio? I would like to know.
Well, octane won't.
But in a carburated engine, the engine produces vacuum that pulls the fuel through the jets.
As the specific gravity of a fuel changes, so will the amount of fuel that gets into the cylinder. So, everything being equal, pump gas has a specific gravity around .755. Most 110 leaded racing fuels are in the .710 to .730 area. If one just changed the fuel, it would be richer as more fuel would be pulled into the combustion chamber.
Oxygenated fuels are available. A lot of pump gas has oxygenates too from ethanol to MTBE. The addition of those additives further leans out AF mixtures.
A common 110 leaded is NOT oxygenated. Some unleaded racing fuels that are easily available have some oxygenate at times.
Lead is available in some fuels. Really, the aromatics and the lead in those fuels can be a benefit when added to pump gas in that 75% pump gas/25% race fuel. Unleaded fuels burn a bit scattered, but when lead is introduced, it usually will contribute to a more uniform flame burn. That can lean out the mixture a little as the AF in the combustion chamber is burned more so than just an unleaded.
Given that one's jetting is "correct", I'd start by cutting the pump gas with a little 110 leaded fuel. The overall mixture will end up having a little lighter specific gravity, have a little lead, and have a little more of the aromatic chemicals that have been pulled out of fuel. It should allow for a little better burn in the cylinder without changing jetting.
Hope that gives you some ideas.
Right, it would. But the lead and the aromatics in a regular 110 style racing fuel would burn more completely thus making it not run rich.
Don't think of it only as a result of the increased fuel, but additionally as part of the process of combustion.
Don't think of it only as a result of the increased fuel, but additionally as part of the process of combustion.
mudsling
Thread starter
I sure have learned a lot.I thank you for your time.
Higher octane will not burn more completely if you do not have adequate compression or very lean jetting to run it...
The fuel won't change the a/f ratio...That will stay the same but you have a slower flame front with high octane and it takes more to ignite it..So if the fuel you're using has octane too high for the compression you will not get complete combustion of the fuel and you're running rich, slowing down, and possibly contaminating the oil...Essentially the same thing as running an A/F ratio that is too rich....The same amount of fuel and air will be going in, but the amount combusted will be different resulting in the same thing as running rich...
Unless you have the head modified and running high compression you might as well save your money..You're not going to get a performance boost with more octane... More than likely you'll get the opposite...The fuel ignites from a combination of the spark and the fuel/air being pressurized...The higher the pressure the more easily the fuel will ignite...That's why low octane in a high compression motor can cause the fuel to ignite prematurely or off time resulting in a knock...So high compression motor needs an octane level suitable for it...And the lowest octane possible without getting detonation and that will give the best performance.
Run the lowest octane possible without detonation and that will give you the best performance and the least trouble....Unless you go with an oxygenated fuel...Then be prepared to richen it up. Run what the manual says and the correct jetting and you will be fine.
The fuel won't change the a/f ratio...That will stay the same but you have a slower flame front with high octane and it takes more to ignite it..So if the fuel you're using has octane too high for the compression you will not get complete combustion of the fuel and you're running rich, slowing down, and possibly contaminating the oil...Essentially the same thing as running an A/F ratio that is too rich....The same amount of fuel and air will be going in, but the amount combusted will be different resulting in the same thing as running rich...
Unless you have the head modified and running high compression you might as well save your money..You're not going to get a performance boost with more octane... More than likely you'll get the opposite...The fuel ignites from a combination of the spark and the fuel/air being pressurized...The higher the pressure the more easily the fuel will ignite...That's why low octane in a high compression motor can cause the fuel to ignite prematurely or off time resulting in a knock...So high compression motor needs an octane level suitable for it...And the lowest octane possible without getting detonation and that will give the best performance.
Run the lowest octane possible without detonation and that will give you the best performance and the least trouble....Unless you go with an oxygenated fuel...Then be prepared to richen it up. Run what the manual says and the correct jetting and you will be fine.
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