Sport_Pilot

Also most aircraft engines have no more compression ration than automobiles.  The lead is needed because the engines have very large bores and the longer distance the flame front travels results in a higher compression of the unburn't fuels by the flame front.  Or in simple terms engines of a larger displacement of the same compression ratio have a higher octane requirement.

eddieC

My Feedback: (2)

The A&P's at the airport I work at won't put avgas in a lawnmower or aircraft tug. They know it's bad for the engines, mainly due to the lead content.  Avgas does have a smell, it's just not as strong as auto gas.

I'm amazed at the folks who ignore the manufacturer's recommendations. They're just whistling in the dark... 

Firepower R/C

My Feedback: (10)

Well, like I said, you can split hairs here...

"Also most aircraft engines have no more compression ratio than automobiles." Ok, but this doesn't matter, does it? By your own description, "The lead is needed because the engines have very large bores and the longer distance the flame front travels results in a higher compression of the unburn't fuels by the flame front..." In a nutshell it allows higher (effective) compression caused by the long flame front propagation distance.

Static or Effective compression... the lead allows it to be higher than without it without detonation/damage, which was my point. I was trying to keep it simple.

In addition, aviation engines do have trouble with fouling plugs quite often, as the lead will foul them as Zeeb said. This is due to a rich mixture. This situation can be minimized with a proper mixture setting/ carb setup.

I will bow out of this topic wishing all happy engine running, but state: Large or small, engines have to be set up for the particular fuel they use to get the most out of it... a small engine can run on 100LL just fine if set up for it. Is it worth it to do? Probably not.

It might be worth doing some testing... could be fun!!!

OliverJacob

My Feedback: (12)

I think it is worth a try. From what I see here - spark plug fouling is the worst that can happen.
So you should not run too rich. Also in a full scale plane spark plug fouling happens mostly if your engine idles for long periods of time. In flight you should make sure to lean it out with higher altitude / lower air pressure.
I guess it would be a good practice not to let your rc engine idle for too long.

Sport_Pilot

No, because that is what happens on low octane gas.  And the compression is way too high causing detonation.  With high octane the flame front burns slower.  Also this is the actuall presures I am talking about too much causes detonation, this is not the compression ratio which is another thing.

Sport_Pilot

Not to mention stuck valves, clogged and rusted out mufflers, stuck rings, filthy oil, worn bearings, and possibly many other problems.

You are talking about carbon fouling. Although a lean mixture will help with lead fouling it won't get rid of it. Having a high compression ratio is the best way to deal with lead fouling from leaded fuel, and that only reduces the problem.

Antique

My Feedback: (4)

How come no one talks about the lead helping to lubricate the valves is a 4 stroke ??
We ran leaded fuel in EVERYTHING starting in about 1909 with the first Model T...I have a 1912, leaded fuel would be no problem...Even runs on kerosene..Smokes a lot with that Compression ratio is 4:1....

OliverJacob

My Feedback: (12)

The smell is really an issue. Some people here have large glow engines, burning lots of fuel and the next hobby shop is about 1 hour away.
Only reason they do not switch to gas engines is the smell, which is definitely a problem if you store your planes in the house.
Maybe some engine manufacturers are watching and offer a model which is rated for Avgas use. I'd be very interested and so are many others.
If it's just the compression ratio - maybe someone could offer modified cylinder heads.

Sport_Pilot

I have never seen lead do anything but jam up in the guides and cause valves to stick. Perhaps the low leval of lead in the old amogas did that, but 100 LL Avgas has more lead than the old premium mogas did.

eddieC

My Feedback: (2)

I keep my 1/4-scalesprint car in the house, no one knows unless they see it. Tank has fuel in it, but i do clean the car after runs and plug the exhaust.

OliverJacob

My Feedback: (12)

Back in Germany my '84 Beamer was rated for leaded gas. Since '94 leaded gasoline bacame illegal to use in cars.
So even with the highest quality unleaded gas this car sounded like a diesel under high loads. You could hear every valve hitting the seat.
Even with the additives you could buy it was still noticeable. That car needed lead, so I sold it to russia, they still had leaded gas.
But back to the topic, I am running only 2 stroke gas engines. I don't think lead will make them run better, but will it hurt them?

Sport_Pilot

Sounding like a diesel and hearing valves hitting the seat is a problem with low octane.  The early unleaded fuels had lower octane than the leaded fuels, causing knocking.  100LL has 20 times the lead of the old leaded regular gas.  The lead will not only foul the spark plug but also the rings and muffler. 

airraptor

My Feedback: (66)

You need to quit asking the guys on here we are no expert but most of us think we are experts lol.

The AV gas/Race gas comes up all the time in every sport with running engines. I seen it many times in the ATV world. seems about every five or so years someone new asks the question.

yes you can make 100 run better in your engine than pump gas but ist not worth it. AV gas was designed for full scale airplane engines to run a at a steady state rpm.

Then there are they guys that think if i run race gas in my engine it will be faster lol. I seen it in cars, ATV's and even in here. A guy wil ask what fuel you running the guy will smile and say " I only run race gas ". Most "race gas" gasoline's have a high octane rating. these are set up for a computed "measured" compression ratio. measure compression ration is different than "running" compression as it can be more or less depending on the engine. In 4S the cam can bleed of compression with valve overlap and be higher at top rpm. same with two strokes as they can be lower at idle then one on the pipe can be way higher. Running a high octane fuel in a low compression engine will allow the chamber, piston top and exhaust port to "carbon up" faster.

The compression ratio I believe in most of our two stroke gas engines are in the area of 7-1 to 9-1. If you take that 7-1 engine and make it 11-1 and run some good 100 race gas (not AV gas) you will see some gains.

If want a different smell to your engines VP sells some really good "race gas" in 93-94 octane that can order with different scents like strawberrys, cherry and so on.


So if you want good quality advice go do some research on gasoline, how engines work, read how to read a spark plug, read a piston/chamber and many other areas as you will be better informed than most of the guys on here will give.

Yes some have used it and had no issues and some have. i bet the IMAC guy is sponsered and his engines get sent in a lot to make sure in top form.....

I would never run AV gas in anything other than a real airplane.

hobby_man

My Feedback: (8)

.

I have a 1976 Grumman AA5A Cheetah, I get asked this question all the time, I quote my old wise and knowing instructor told me, 100 Low Lead is for Airplanes

pe reivers

+1
+10!
NO engine of ours needs the 100LL avgas. If you must use it for personal reasons, or because you screwed up your engine with too high a CR, then please adjust the ignition timing to make the best of it.

aussiesteve

I would be very worried if whatever fuel I planned on using was a threat to the inlet and exhaust valves in my Quadra or Zenoah. I know for sure they are very hard to obtain as spare parts.

You have your answers. 100LL will run in the engine. and will have less smell but there is a risk of it causing damage due to chemical reaction (In some engines - don't know exactly on the Zenoah and Quadra - anyone wish to talk about alloying of the surfaces of Aluminium components at combustion temperatures?) and due to fouling and due to increased heating. It also is stil burning when it dpearts the exhaust in a high revving engine (Full scale engines really don't run much above 3000 RPM).

Less smell = less warning sign that fumes are building to a potentially dangerous level (When I was 17 years old, I witnessed a person die from exactly that when the S.O.S lab exploded at the Caterpillar dealer I was working at in West Australia - fumes built up to ignition point).

Warbird Man

My Feedback: (95)

I love the smell avgas in the morning, smells like... Victory!

Seriously, I think It's more important to use a good quality oil and find a premium pump gas without ethanol in it.

aussiesteve

Yep - I use Premium pump Gas and 40:1 of a good synthetic oil (Mobil 2T Synthetic) in ALL my 2 strokes (15cc - 420cc RC Gassers, Chainsaws, Weed Whackers, etc) They all work VERY well.

I tried the "Manhattan Oils" fuel scents for a laugh once. Got a few different ones but the one that smelt like "Reefers" (It was called something like "Wicked Reefer" sure got some interesting lookas around the pits when people were looking to see who was smoking that substance.

[link]http://www.summitracing.com/search/Brand/Manhattan-Oil/Product-Line/Manhattan-Oil-Fuel-Fragrances/?RC=100[/link]

WWIIP38

My Feedback: (43)

I recently asked a USRA representative involved in AT-6 / Zenoah G62 racing about using 100LL in G62 engines. This was his response;

By far the biggest performance factor is the gasoline octane rating. The G-62 was designed to run on crappy low-octane fuel, around 80 R+M, and power output will drop as octane rating is increased. With VP race gas the G-62 is a dog, best with cheap-o pump gas without too much alcohol in it. Unfortunately, the gas-o-hol Nazis have made straight gasoline harder to find in many areas of the country and the added alcohol will play havoc with the carburetor diaphragms after a while.

Scota4570

I did not see the oil that makes your exhaust smell like pot smoke. I need to get some of that for my dirty trick arsenal. Put it in somebody's gas tank and the cops will be pulling them over and searching their car, over and over, and over again! Yet, they are completely clueless. Good stuff when you need it.

Oh, the gasoline smell? Stick a golf tee or nail in the over flow from your tank. That way it don't spill inside your car and stink up the place.

eddieC

My Feedback: (2)

The days of diaphragms and floats being affected by alcohol in fuels were years ago. Current carbs aren't affected.

WWIIP38

My Feedback: (43)

Check out; http://www.ebay.com/itm/Manhattan-Oi...81940649104036

aussiesteve

Yep - I purchased mine from the Aussie supplier (who stock the Reefer Madness).

Little tip on the dirty tricks dept - I loaded the Missuses Jeep with it (she is one of the most straight people you could ever come across) - it was hilarious to see peoples faces when she turned up at a horse event - trick is not to overdose it in the tank otherwise the effect isn't as good.

Couple of guys at my field still believe I am trialling "Hemp oil" as a lubricant in my engines (from legal sources of course). I told them it works really well at 100:1.

loopdeeloop

My Feedback: (4)

By golly if 100 octane AV gas is good for your engine, why not run E-85 which is 104 octane. Seriously there is no advantage to running higher octane fuel in an engine that is not designed to use it (or unless the engine has a tendency to detonate). Unless the engine has a detonation sensor or some other way of determining when detonation is about to occur, the engine managment system cannot automatically advance ignition timing to take advantage of the increased octane. Case in point. My Chevy Impala can run on corn squeezin's (E-85) just fine and it performs better than it does on 87 octane regular although it uses more of it. (It is currently 60 cents/gallon cheaper than regular right now.) The reason is that the engine management system knows what the fuel mix is (E-85 vs Regular) and adjusts the injector pulse width and ignition advance accordingly keeping it at just below detonation levels. Model engines do not have that capability so unless the engine is modified to run the higher octane fuel, it is a waste of money. Someone also said higher octane fuel burns hotter than regular. That is also incorrect. Higher octane fuel buns slower, hence cooler to reduce the tendency for the engine to detonate in the first place. If you advance timing on a model gasser to say 34 degrees rather than the traditional 32 degrees, and increase compression a tad, then there would be an increase in power since the engine can take advantage of the increased octane without detonating. It is the tuning changes that make the power difference. The higher octane fuel simly allows the engine to be operated under those tuning conditions. It is also true that higher octane fuels contain additives that two stroke motors don't deal with very well. So the answer to the OP's question is try it and see. Nobody can give you a positive answer. If your engine was designed to provide maximum power on 87 or 92 octane fuel and it runs better on 100, then it was not tuned properly in the first place.

captinjohn

AJ, if you really do not care....why are you yapping about it yet? I have a snowblower that started hard for years...I put some AV gas I had for my Motorcycle in it and it finally started like it should...first pull.

You guys that do not try new ideas are just screwing youself. Capt,n