2 stroke leaded fuel

[quick2008]

Hi Guys,

Wondering if anyone can help me out in the fuel department.??

The long lived debate between avgas users and hi octane unleaded, in outboard racing has always interested me.

My understanding is that tetraethyl lead was introduced to "fuel" years ago to raise octane levels, and for exhaust valve seat protection in 4 strokes

Obviously emission laws have faded leaded fuel out in Genral automotive vehicles, but aviation industry still use leaded fuel (avgas) for its exhaust valve protection and its anti knock properties.

My question is, is there any benefit in "avgas" other than its anti-knock properties required in high perf. 2 stroke, or any high compression engine?

Cheers Guys,

quick2008:)

[Master Oil Racing Team]

I only raced with gasoline once, and at that time unleaded had not been formulated, but I was friends with a lot of OPC guys and they always used avgas. Seems like unleaded started appearing on the market around 1970 or so. I think the outboard racers must have found that the avgas was superior in the 2 cycles as well. Leaded gasoline was important for the high compression 4 cycles, but when laws reducing the oxides of nitrogen came into effect, compression had to be reduced and there were a number of years where engines really sucked as the design engineers had to figure out how to comply with new laws.

Seems like in 1975 or 76 that the European OPC racers were banned from using avgas. I kind of remember that before there were field tests, there was a little bit of smuggling going on. The airports were not allowed to put the fuel in anything other than an airplane, but you know how that goes.;):D Lars Strom could probably give you the inside story on the history and whether or not there were benefits.

[721 Jr.]

Give me a call Norso Lubricants 916-517-5998

[fyremanbill]

As for leaded vs unleaded, the lead residue coats everything that comes in contact with the burning fuel. It stands to reason that it has some level of lubricating value on pistons, rings, and cylinders. It's also difficult to achieve really high octane ratings in gasoline without the use of TEL.
As for the use of Avgas, I'm sure there are better racing fuels made. However, Av works fine on moderate compression engines and I've used it for decades without a problem.

[Mark75H]

Any difference, benefit or problem depends on the motor and compression ratio.

Tetraethyl lead by itself eats up valve seats. The actual additive package contains lead (as the octane performance enhancer) and some bromine compounds that counteract the valve seat recession problem.

Between 1965 and 1971 super high octane street gas could have had between 5 and 8 times as much lead as current AV gas. Some of that 1960's stuff did cause "lead fouling", but modern mixes aren't anywhere near those levels in AV gas or leaded racing gas. AV gas is always the same, the formula will not be changed, discontinued or replaced. A major advantage.

There are pros and cons to both, the pros for AV gas are that it is almost universally available without extra shipping costs and never has oxygenates to change mixture ratios or anything else that will attract moisture or co-dissolve moisture into the mix.

Cons to both are that if you aren't racing and having your fuel tested, the pros probably do not out weigh the biggest con of over octane ... sluggish performance from the peak cylinder pressure and torque being lower if your timing is not advanced to synch up with the best tuning for the fuel you are using.

[quick2008]

Thanks Sam,

I can see the pros and cons of the two,

As for Avgas, ive read lots of stuff around the net+ books, (and yes dont believe everything you read on the net)
These are NOT my opinions, just what i have read/stumbled across
which is why im putting the question up for debate. some things ive found,

1. Avgas hard on rings??
2.It has a chemical property in it designed to clean/remove oil to stop aircraft plugs fouling?
3. carbon build up can occur over time??

and the final, i lost count of how many times ive read that it
runs cooler than..../ runs hotter than...

I understand all of these would be subject to the individuals engine.

My assumptions in general are if you can get QUALITY race gas, use it??

:confused::confused::confused: anyone, lol

quick2008:)

[SkyHarborCowboy]

There is more to Avgas then just the lead content. For example, the Vapor Pressure of the fuel is different then normal or race gas due to the altitudes that it is designed to be used in.

Joe

[Don Muncie]

After years of experience running aviation fuels in all kinds of engines, there is absolutly no worries about doing so! Out here in Oregon, we just went through one of the worst snow events in recent memory. I have a mercury snow mobile that last ran in 1990 on 100/130 avgas. There was still about a gallon of that fuel in the tank..the forth pull and I was pulling cordwood to the house!

As far as aviation in outboiard racing goes, it's not manadory to use it, it ain't any faster. What it does do for you is this, your setting will always be the same (no more F'ing around with jets or timing) The fuel will always pass the meter and you can store this fuel safely for five years! It also burns much colder than any other perolium based fuel out there. It burns super clean and is very safe for the environment and should be made readily available for two cycle engines!

Have no fear in using the 100LL aviation fuel, you'll be glad you did!

[Mark75H]

There is more to Avgas then just the lead content. For example, the Vapor Pressure of the fuel is different then normal or race gas due to the altitudes that it is designed to be used in.Joe

Joe is correct ... no one wants to get vapor lock at 10,000 feet. And what Don Muncie always says is also correct ... it has fewer of the components that decay and make gum and varnish as regular street gas does. One of the specs is that it must last a minimum of 2 years in storage.

It is no different on rings and has nothing in it for any extra combustion chamber or spark plug cleaning. Carbon build up depends on fuel mixture for any fuel, nothing special or specific about AV gas. Cooler or hotter also depends more on spark advance and mixture than the particular fuel.

[looseunit225]

as a aircraft engineer in my earlier days i can tell you from our study's on Av gas in Australia we have Avgas and we have LOW LEAD avgas the low lead is slightly lower in octane but its good for the turbo'ed engines something to do with comppressing the fuel before the stroke of the cylinder!

Avgas wont increase carbon build up! carbon build up has got to do with how you tune the engine!

avgas doesnt have any additives in it that were designed after WW11

it is better for cylinder rings because the lead gives upper bore luberication!

once again the best thing about AVGAS is it takes for ever to go off doesnt attract water!
and best of all it hasnt changed its generic make up since world war 2 as with aircraft if it works dont change it stuff the enviroment bassicly!

i mean just look at the engines they have in the plans ??? you cant get much more simple than them!

[Bradkitcher]

Hi Norso Lubricants

Can you please give me advice on racing fuel, oil and plugs for a tohatsu 2-stroke 15hp

Regards

brad at kitchergroup dot com

[Rotary John]

The primary benifit of Av gas is the higher octane rating; 100 mim. It used to be 130 octane. The higher octane allows higher compression ratios and advanced timing (more power) because the higher octane prevent detonation. We used to run Av gas in our 2-cycle racing engines back in the 70's even when auto gas had lead in it also. Lead also acts as a lubricant for the rings, but leads to more and harder deposits. When lead was removed from auto gas in the 70's, problems with coated rings and rubber parts were numurous, along with reduced power to prevent detonation. My '79 Corvette 350 had a wopping 170 HP. Vitually all modern engines are designed and tested to run on non-leaded gas, including outboards. An octane booster will allow the same engine modifications that Av gas allowed and a much lower cost.

[Mark75H]

What about using it in stock motors with 6:1 compression ratios?

[Rotary John]

What about using it in stock motors with 6:1 compression ratios?

Don't get me wrong, AV gas won't hurt yor engine. I suspect a race engine is torn down and inspected on a regular basis, so if piston deposits are getting heavy, they can be cleaned off. I guess my point was if you don't need the higher octane to prevent knock and detonation, there isn't any benifit in running Av gas in modern engines.

[calvin]

Some have warned against using hi-test in 2 strokes because of why they could not explain..would this be an issue?

[Mark75H]

The problem is not necessarily 2 strokes, but low compression motors.

Most 2 stroke fishing motors are generally fairly low compression motors that can not take advantage of higher octane. Some, but not all low compression motors running on some but not all high octane fuels will make less power. Some will make no difference. None will make more power by switching to high octane if the compression is low or medium.

Using high octane gas in a motor that doesn't need it, takes a chance on making less power than running on the correct octane rated fuel for that motor.

[Bradkitcher]

What is high and what is low compression. I tried to work it out and my motor is 12:1. Does that sound correct. Is this high or low.

Advancing timing apparently helps with higher octane fuel.

Does anyone have any recommendation for time advance, why it works, what fuel to use and any oil recommendations.

Thanks guys

[Mark75H]

High varies with bore size and chamber shape. On a two stroke, it is often better to compute "effective compression ratio" rather than full stroke compression ratio as calculated for four strokes.

[Bradkitcher]

Could somebody please calculate my compression ratio or the other type which is called the effective compression ration. Then I would greatly appreciate input to if this is high or low.

I heard that these outboard have a higher compression than outboards of a similar size.

Per Cylinder

Bore 55mm
Stroke 52mm
Capacity per cylinder 123.5cc
Cylinder head height 21.75mm
Cylinder head capacity with spark fitted

Thank you all for your help so far.

[Mark75H]

Need to know the height of your exhaust port

[Rotary John]

It might be easier if you posted what engine you have and what if any modification have been done to it. Some one with the same engine might have the info for you. To be able to calculate your CR you will need to measure the cylinder heard volume at Top Dead Center (CC's). Then your max vol will be your 123.5cc + this head vol. Your min volume will be this head vol. The CR = max vol/min vol. The effective CR is measured just as the exhaust port closes. That is, your effective max vol is (the vol that is left of your stroke at exhaust port closing + min vol)/min vol. Hope this helps.