Fuel Type

[cbxmountainman]

If I'm not mistaken, I have read where premium fuel burns slower/cooler than the lower octanes. I just run plain ol Regular in my CLs.

[hooptytank]

If I'm not mistaken, I have read where premium fuel burns slower/cooler than the lower octanes. I just run plain ol Regular in my CLs.

Correct.

Higher octane burns slower, keeping the fuel from exploding in the combustion chamber of higher compression engines, which is what happens when the engine pings or knocks.

So in a low compression engine you may actually loose power. Probably not enough to feel, but may be visible on a dyno.

Basically run the lowest octane that won't ping when the engine it tuned properly with the right timing, points gap, jets, etc

[conbs]

While the issue in this thread is whether your bike will run alright on no-lead fuels, I recently found other issues that I don't know the answer to, but are probably important in the discussion about what should go into your gas tank.

The May '09 issue of Mustang Monthly has an article on new fuels in vintage vehicles. They claim that today's gas has ethanol and other additives designed to "clean up emissions and help sagging octane". Those additives are "especially hard on vintage mustangs with their rubber float needle valves, die-cast bodies, galvanized tanks and lines". They suggest annual replacement of rubber parts in the fuel system because ethanol accelerates deterioration of vintage fuel systems. The issue is deterioration of rubber leads to fuel leaks that can result in fire.

Also, because "ethanol tends to be hard on rubber and cork components, you can wind up with leaks and bits of rubber in the fuel system, which can cause a sticking float and plugged passages.

Also ethanol"tends to be hard on die-cast carburetor bodies" and "zinc and ethanol don't get along well" "Like brake fluid, ethanol likes to retain more water than gasoline."

Is this just a pitch so the vendors that pay for advertising in the magazine can sell more parts? I can't tell. They don't really say whether 10% ethanol is as bad as E85, but they do say flatly "E85, which is 85-percent ethanol and 15 percent gasoline, should never be used in a classic mustang."

Anybody heard about these claims? The fuels systems on Honda's are much simpler than on a Mustang, but if these are real issues, with the scarcity of many parts shouldn't we all be paying attention to them?

[LOUD MOUSE]

Were I to be able to read the exhaust temperature with regular gas/fuel or high octane which should I see the higher temperature at the same distance into the exhaust pipe?. (4 inches in particular) ................lm

If I'm not mistaken, I have read where premium fuel burns slower/cooler than the lower octanes. I just run plain ol Regular in my CLs.

Correct.

Higher octane burns slower, keeping the fuel from exploding in the combustion chamber of higher compression engines, which is what happens when the engine pings or knocks.

So in a low compression engine you may actually loose power. Probably not enough to feel, but may be visible on a dyno.

Basically run the lowest octane that won't ping when the engine it tuned properly with the right timing, points gap, jets, etc

[jwbert]

I try to run the fuel that does not contain any ethanol, which is usually the 91 octane where I fuel up.

[sotxbill]

Were I to be able to read the exhaust temperature with regular gas/fuel or high octane which should I see the higher temperature at the same distance into the exhaust pipe?. (4 inches in particular) ................lm

I would be surprised if you see any difference between high octane and low octane. If your engine is not pinging, either fuel should burn the same temperature and have the same power.

BUT if your compression is so high that it pings or knocks, then a higher level octane will fix it and burn correctly to give it more power. but once that level is reached, adding more octane will do nothing. no more power in higher octane fuel.. just more lead or other additives to keep it from pre igniting.

so I would be surprise to see any difference between the temps of high octane vrs regular if its not knocking. should be the same. Explosive forces are the same under this example, this engine, this compression level. higher octane might be a tiny bit less temp, but I would be surprised if you could measure it. The btu content would be the same and burn fast enough to completely burn through the cycle. All of the usable btus would be given up, even if it took a billionth of a second longer for high test to burn. The difference should not be significant.

Sound plausable????? anyone have some lab results?? or a myth buster episode?? thought I would throw in my best quess.

[teazer]

It's an old thread, but many questions were left unanswered.

100ll is designed to burn slowly in a slow running aircraft engine. The old myth about it being good for performance came back in the 50s when gas was about 80 octane and compressions were low. The car guys wanted more compression and that caused detonation, so if they were able to beg borrow or steal some av gas they could run a higher compression without meltdown.

So higher compression was the power generator. Av-Gas allowed them to use it.

We found on the dyno that 89 octane made marginally more power than VP C12 with a smoother power curve - that was on a full race CB160 turning 11,500 with raised compression.

Some race gas burn faster than others and a faster burning gas will have more burned before it leaves the exhaust port. Others are slower burning. Some have a low evaporation curve and some don't evaporate until at least 100 degrees higher.

All the gas is not used before it exits the port. Poor atomization and non effective squish mean that some of the larger fuel droplets are still burning as the gas goes down the pipe.

A hot running two stroke may well reduce it's EGT with a race gas, but it has to be the right gas. Sounds like LM got lucky that time.

Any more octane than a motor needs to avoid detonation is a complete waste of time and money and usually results in less power and a lighter wallet.

The only thing I really like about leaded race gas is that it tends to burn cleaner than unleaded and needs a cooler spark plug which is much easier to read at the race track. Unleaded tends to leave a sooty deposit and often needs a hotter running plug to keep clean.

Ethanol and methanol are hard on fuel systems, but we don't have rubber tipped float needles, or galvanized fuel lines, so that is less of an issue. Ethanol will leach the resin out a fiberglass tank though.

E85 is a whole different story though. It generally needs larger jets, more spark advance and can stand much higher compression. Alcohols generally need to be jetted differently than gasolines.