I have recently converted a Ryobi 31 cc and I have been told to try using Coleman fuel/oil mix instead of gasoline/oil mix because it burns cleaner and has a higher octane. Have any of you tried this combination? My engine seems to run well on it, but it seems to be quite warm after I stop the engine. I am running 32:1 mix with the Coleman fuel. Thanks, Mossback

I doubt that its running any warmer?

Coleman is much lower in octane than regular unleaded.

It doesn't necessarily burn cleaner.

The biggest advantage or difference is that Coleman smells better and your wife will not object to it.

Enjoy,

Jim

I wonder why Maynard Hill used Coleman camp fuel rather than gasoline in his transatlantic model plane flight. The engine was a OS .61 4stroke with spark ignition, and a carburator from an OS .10!

BTU's per oz. Mainard engine also runs around 4000 rpm with a very modest load., at 2oz per hour fuel burn it is not making much heat

OK---Lets step up the stakes on this one. Has anyone tried 105 Oct. racing gas in there weedy? No telling what kind of oil mix you would need on this one. Hooker53

The racing fuel will make your gas engine run hot. It will not have more power.

Enjoy,

Jim

w8ye,

Would you care to be more specific about your statement? I have the following questions:

1- Have you experimented with it?
2- Why does it work on engines that have higher compression ratios, and or may be super or turbo charged?
3- It's used on engines that are not only for dragracing, why would it not work on engines that are less demanding.


Thank you

TKG did some very exacting tests a few years ago on this, there should be some info somewhere in the old files....
There is a world of difference between a 6000 hp supercharged 4 cycle dragster and a 2 hp low compression weedeater 2 stroke...

If 105 octane racing fuel would work in a weedie someone would already be doing it..

Unless an engine has high compression, like a racing engine, it does not need the increased octane rating of racing gas. Supercharging or Turbo'd engines also need high octane gasoline, depending on how much boost they are set up for. Generally, higher octane fuels actually have LESS inherent energy, but because they permit an engine to run safely with much higher compression ratios, the engines develop more power. If you run high octane fuel in an engine that doesn't require it, like our weedies, you will be doing several things:

1. Losing some power.
2. Wasting some money.
3. Carboning up your engine and spark plug from the un-needed additives in the fuel.

Hope this helps,
AV8TOR

I wouldn't recommend this for everyone....but it works for me...most of my motors are the low budget type...(she's still not over the motor missing out of her weed eater.)

Wife did wrinkle her nose at the smell of burnt oil...[&o]
Local racing shop has small bottles of stuff that makes your exhaust smell like cherries, bananas, cinnamon etc..

One tablespoon of the stuff to one gallon of gas makes a world of difference to her.
I've not seen that it's done any damage to the motors..

I've found
Really no advantage to Colman fuel...
Avgas, you have to know someone to get it without a license.
Todays hi-test pump gas is days gone by regular..
Racing fuel (here) is $6.00 to $8.00 a gallon
Racing methanol is $4.00 a gallon if you buy 5 gallons at a time, for mix you're own glow..

OK---this is a good discussion. But--I'v still not heard anyone say what is the best to run in these conv. engines. From the lines I'm hearing, I gather Reg. (87 Oct.) with a 32: to 50 : mix of Amsoil. Right. Hooker53

High octane slows down the burn rate of the fuel to stop detonation in high comp. engines. So its just not required in the low comp engines because there is no detonation.

You got it....Pump gas......
Break one in with either LawnBoy Ashless, or Pensoil for air cooled engines then switch to a synthetic......I'm not going to say what brand name....tooooomany different opinions.

Yes, be sure to break your engines in on regular oil like Pennzoil for air-cooled engines, and THEN switch to synthetic if you want to do so. If you use synthetic from the beginning, you might glaze the cylinder walls, and the engine will never seal; (break in). I would say though, that 32 or 50 to 1 would be way too much for Amsoil. More like 80 to 1, perhaps even 100:1. Be aware that synthetic oils do not offer very good long term storage protection, and can absorb moisture from the air. Therefore, if you are not going to fly for a while, an after run oil treatment would be a good idea. (I use 3 in 1 oil for this.)

Most weedie gurus recommend regular 87 octane car gas, though 89 might be a good choice if you have raised the compression. Do try to find gasoline without alcohol, as the alcohol readily absorbs moisture out of the air, and this doesn't mix well with the oil in your mixture. We have a lot of problems with this in Ultralight airplane engines, and resultant engine failures.

AV8TOR

High compression=the need for high octane. Whether it be static compression or forced induction.

87 will make the most power. Its actually the cleanest gas also, less additives.

One thought, I would buy any gas I would use during the summer when there is no MTBE in it. MTBE seems to lower power and gas mileage in my car, so it must do the same in a plane.

If you want an extra power boost, hook up a small bottle of NO2, the kind used for making whipped cream, just don't forget to add more fuel to it too. j/k

Preignition has to do with the rate of flame travel among other things like compression ratio. The additives to make higher octane gasolene have substances like MTBE added that slow the rate of flame travel down.

With a model 2 cycle gas engine running 7,000 rpm, that's 7,000 combustion cycles a minute. That would be like your car engine running at 14,000 rpm. Firing at this speed, the rate of flame travel is a mute point considering the relatively low compression ratio of the typical gasser.

Coleman fuel has a much lower octane than 87. Perhaps as low as 60 octane.

Enjoy,

Jim

Oh boy........

I hear a can of worms opening....Whirrr, whirrrrrr.

7,000 rpm = 116.6 firing cycles per second...

Coleman fuel has a much lower octane than 87. Perhaps as low as 60 octane. Why doesn't it ping in your gasser?


I'm agonna bite on this one...
It would be the fastest burning of all the others..

This has all been hashed over before over in the fuels forum last summer. That was the situation that some fuels engineer finally came on there and said.


--------------------------------------------------------------------------------

Tommy Meisel says:

I gotta chime in as a mechanical engineer (retired) who has a basic understanding of engines and combustion processes. The size of the combustion chamber in these small two cycle engines and the frequency of combustion (at 7000 rom you light the fire 117 times a second) does not allow secondary flame fronts to form and collide with the primary flame front and cause ping. On your four stroke automobile, at 4000 rpm you are lighting the fire 33 times a second. A secondary flame front caused by preignition (aggravated with higher compression) has enough time to make it ping. Higher octane fuel just burns slower, that all. By the time any secondary flame front meets the primary one, it is too late.

Engines are designed to utililize certain fuel characteristics. On an engine that would be ping limited, if the manufacturer knows you are using a high octane fuel, he can raise the compression ratio, increase the timing and change the valve timing and overlap to increase power. Some do.

But our model engines are not ping limited.

Our gassers are pretty oblivious to the octane of the fuel. If it runs without preignition, the octane is high enough.

The manufacturer may specify higher octane fuel for other reasons, maybe he feels it has less additives, maybe he feels it gives him a competitive advantage by making his engines appear more sophisticated and needing "better" fuel. Who knows?

_____________________________


Enjoy,

Jim

Now that's exactly right and well put. One of the reasons full size airplane engines have two spark plugs in each cylinder is to properly ignite the mixture in the very large bores common in those engines. This is also why they need high octane fuel; the large bore size. Our small (tiny by comparison) bore weedie engines are a different matter.

AV8TOR

I thought ping in an automobile engine was caused by the ignition firing too soon, and the piston is not all the way up.
So the piston is trying to compress an explosion that already happened. The ping noise is your connecting rod bearings slapping around.
I never heard of secondary flame fronts. But I am not an engineer.
Doesn't matter what octane you have, you can make an engine ping by increasing the timing too much.

I understand about the higher octane slowing the burn process down.

Check this out, a top fuel dragster only makes around 500-600 revolutions of the crank to get down the 1/4 mile.

It's a complicated subject. There are two things that can occur. One is Pre-Ignition, and the other is Detonation. One can begin and cause the other. The cures are, higher octane fuel, less ignition timing advance, lower effective compression ratio, water/alcohol injection, etc.

Pre-ignition is caused by either the timing being too far advanced, or something in the combustion area setting off the combustion too soon, such as a glowing piece of carbon, a spark plug electrode being too hot and actually glowing, etc. Detonation, is usually the auto-combustion of the mixture in some area of the combustion chamber, and this burning flame front colliding with the one initiated by the spark plug. These occurrences are most problematic in engines with large bores, high compression ratios, (or effectively high compression ratios due to super or turbo charging), and advanced ignition timing, though the problems can occur in many engines if the conditions are right. Even a low compression smog era car engine will ping if the fuel is crappy enough. It is a very destructive condition for the engine, with everything involved taking a beating, to include pistons, valves, bearings, etc. I have seen pistons with holes burned completely through them caused by detonation, and valves beat up into their seats so badly that the heads were unuseable.

The cure is to use proper gasoline for the application. However, using a fuel with a higher octane than the engine needs is nothing more than a waste, and can cause increasing combustion chamber deposits and spark plug fouling.

Hope this helps clear it up a bit,
Take care,
AV8TOR

One more point. The fact about higher octane fuel burning slower is exactly right. The lower octane fuel cannot tolerate as much timing advance because it burns faster, and the combustion process is too far along before the piston gets to the top. It is important to remember that we want the fuel mix to burn and expand; not explode, and that we want the peak pressure of combustion to occur around the time the piston is passing top dead center. This gives the most power, and is why we light off the mixture before top dead center to begin with. This is easy to visualize while adjusting the timing on a running engine. The engine will increase in speed, (and efficiency) as you advance the timing from a too slow position, and then start bucking and running rough when you get to the too advanced point.

AV8TOR

I realize that one. Thanks.
I just had never heard of a second flame front, I found it to be interesting.
I have built a few street motors, including some porting work I did myself.

av8tor,

Thanks for setting the record straight, your clear and easy to understand explanation of the differences between pre-ignition and detonation is right on, just the way I learned it in high school Auto-Shop in 1947. Thanks again, [8D][8D]

RJ