Avgas ?

[Mr Geets]

Anyone use avgas? My Mercury 90 efi 4 stroke recommends premium fuel ($1.39.9 per liter here in Saskatchewan - US gallon is 3.79 liters) Av gas 100 low lead looks like about 10 cents cheaper a guy told me at an airort today. Any comments? Thanks.

[Just Laxin]

My friends run avgas but their H.P is any where from 800-1000 per engine. For a 90 HP I have no idea, sorry. In my Merc. 150 efi 4-stroke I run 87 octane.

[RobRoy]

If for only cost consideration I'd stay with the manufacturer's recommended fuel.

Higher octane provides for quicker detonation and therefore some increase in power at the trade cost of higher temperatures and premature fatigue.

No sense experimenting with a $4K engine. ...or whatever it costs.

[STEVEBRENDA]

I did not know that higher octane provides for quicker detonation. My understanding is that it is the other way around and that premium gas is really just a waste of money. (both fuels being E85).

[ronb]

I did not know that higher octane provides for quicker detonation. My understanding is that it is the other way around and that premium gas is really just a waste of money. (both fuels being E85).

You are correct about Octane ratings..

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance

[Bamaman]

It's a shame that gasoline's so expensive in Canada, especially since your country is such a large fuel exporter.

When we were in Italy in April, regular grade gasoline was the equivalent of $9.51 per U.S. Dollar. Obviously, many of the automobiles in Europe are diesels.

Yesterday, local diesel fuel was $3.99, in spite of regular 90/10 gasoline dropping to $3.41 per gallon. We diesel owners feel like we're somewhat being taken advantage of too.

If gasoline gets too expensive, I'll be floating more in the middle of the lake listening to music on the pontoon boat.

[HandymanHerb]

Lead will short out your plugs, when I was racing I ended up getting some leaded gas and it took out all four plugs in a heartbeat, and AVgas is higher in US due to all the FAA taxes on it.

Europe should be giving gas away as no one is using it because all the taxes on it there, that's why our diesel prices are so high in the USA, your politicians are trading our diesel away for their throw away gas.

When you process crude oil into fuel, if your want diesel your by product is gas, same way when you make gas the by product is diesel, that's why we use to throw it away for years in the USA and it was the cheapest fuel, but since they figured out they can sell it to Europe for a higher price, our price went way up from being the cheapest to the most expensive.

Doesn't bother me you say, you don't use diesel, WRONG, we all pay for diesel every time your buy something, it all gets to the store by diesel, ship, trains or truck, so every time the diesel goes up, so does the price on every thing you buy, we end up paying for Europe's high taxes on fuel to cover their health care.

[Bryden24shp]

I did not know that higher octane provides for quicker detonation. My understanding is that it is the other way around and that premium gas is really just a waste of money. (both fuels being E85).

You are correct about Octane ratings..

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance

Yep the higher the octane, the more efficient the 'burn'. This also equates into better fuel economy at the far end of the spectrum. I used to run 103 AvGas when I had my 440 GTX, when running regular, it would knock like crazy. It was high priced back then, like $1.98/ gallon compared to $1.30 or so. Today, I use only Shell 93 Octane in the truck with all its high performance shit on it and am supposed to use it in the boat, but its hard to find it when your on the water. Its 100% gas. No ethanol. But now in the winter, its rated at 91 Octane, because of the conditioners they put in it. And now that I'm done towing the boat to hell and back, its cool.
I know of some people who mix Pump gas with AvGas for their HP boats, to raise the octane. Oh the good ole days...

Herb, I wonder if anyone has ever thought of a diesel outboard. Of course, you're right, with the cost, it would'nt matter!

[HandymanHerb]

I know I went from using 24 gallons of gas a week to 4 gallons a week of diesel when I bought my used Kobota, but diesel are heavier so will keep them off small boats for a while longer.

When my mower quit but the engine was still working fine, I was thinking of using it in my toon, I know it would have been better on fuel usage and would be faster than my 50 horse Evinrude even with only 26 horses, but was to busy working back then.

[ronb]

Yesterday, local diesel fuel was $3.99, in spite of regular 90/10 gasoline dropping to $3.41 per gallon. We diesel owners feel like we're somewhat being taken advantage of too.

I always thought that diesel was the 'left over garbage' from the gasoline making process. But the problem you are probably up against is shipping/trucking/logistics, trains, and farmers (its harvest season).

$3.41, the cheapest I saw it on the way to work was $3.59... and we both pull it from the ground here (crude oil) AND make our own Ethanol.. (there is an Ethanol plant about 20 miles West of Fargo in Casselton)

FWIW. Mercury has a contract with Cummins to sell I/O diesels...
http://www.cmdmarine.com/

[HandymanHerb]

No the problem they can sell our diesel for a higher dollar to Europe because they have all switched to diesel for the best fuel mileage because of the high taxes on their fuel, so even though diesel takes less processing, out of a barrel of crude oil, you going to get only so much diesel or gas, now in America we crack the crude to get more Gas, but part of the process makes diesel.

In Europe they crack the crude for the most diesel, so their by product is gas, which they can't sell in Europe, so your politicians made a deal to keep gas prices down with cheap gas from Europe, but then that drives up the price of every thing we buy.

So no it's not just something going on by local farmers, it's our politicians selling us down the road again.

[sammyphsyco]

A) don't run any more octane than is required to prevent pre-ignition and or detonation. There is ZERO performance gain beyond that point and no fuel economy to be gained either.
B) avgas is designed for engines that run at altitude, run a steady rpm and have diffrent requirements than boat or car engines.

[belercous]

I'm quite familar with AvGas from my days of being an A/C mechanic. Most AvGas sold nowadays is 100LL. The LL means "low lead," which it is for 100 octane gasoline. Do not be4 fooled, it's low-lead, but only for 100 octane gas. 100LL contains a lot of lead. The lead will build up on pistons & will throw a high-reving engine out of balance. This is not critical on A/C engines since they rarely spin over 4K/min.

But the 100 octane rating is for a stoiciometric mixture which is the optimun fuel/air mixture. A stoichiometric mixture runs hot. Don't wanna do that. It'll burn out exhaust valves & pistons, in that order. 100LL AvGas is rated as 100/130, octane-wise. If rated as an automotive fuel it would be 130 octane. 130 is the octane rating for a rich mixture. The equivalent AvGas (if they sell it anymore) of 87 octane (auto fuel) is rated 80/87. 80 being the stoiciometric mixture, 87 being the rich mixture. Automotive gas is rated using the rich mixture octane figure.

I've rebuilt many small A/C engines, and also pulled/replaced jugs on the same. Everyone of them, all using 100LL AvGas, had considerable lead deposits on the pistons, heads & valves. You could scrape it off in chunks. Which I've done. On low reving engines, this is no problem. But on higher reving engines it will throw the reciprocating parts out of balance. This is not good. Most A/C piston engines spin well under 4k at W.O.T., which is usually only on take-off or emergencies. (although some may rev a bit higher, depending upon the installed prop).

The genearal rule is to not run a higher octane-rated fuel than is needed to control pre-ignition. A higher octane rated fuel is just wasted money, and in the case of running AvGas, could be detrimental. However, what usually happens at higher RPM's is that the lead deposits tend to break loose & fly off. Still, not a good idea to run AvGas.

An engine experiencing pre-ignition or detonation is not good. Perhaps some have heard the sound: the valves pinging in a car upon going up a hill or under hard acceleration is it. Quite hard on an engine. 2-stroke engines don't have the same sound (no valves to slam shut). Running a high lead content fuel, such as 100LL (or above) AvGas WILL leave lead deposits. Lead deposits WILL cause hot-spots (they glow red) which WILL cause pre-ignition. This will defintely ruin an engine. Bent connecting rods or holes in the piston: this & burnt valves in a 4 stroke. Running a piston engine overtemp will also glaze the cylinder walls which will reduce the engine's compression, & in a 4 stroke engine, cause high oil consumption.

(Also note that there is NO octane in gasoline, it's only a comparative rating system: Iso-octane being 100, Heptane being 0.)

Just my $.02 worth. Sorry for the diatribe.

[oldmn19]

I think the main point is as stated by several above, running higher octane then required to control pinging or knocking is a total waste of money. Plus any lead will shorten the life of spark plugs dramatically. If your as old as me you probably remember changing spark plugs about every 10K miles because of misfires. Today we see plugs lasting 50K to 100K miles, thanks to no lead and tighter engine tolerances, less blow by the rings and better oils. One last thing if your caught using AVE gas on the highway your subject to a nasty fine.

[WILD MAN]

When I was a kid my dad had some crop-dusters so when I needed gas for my motorcycle and didn't have any money I would "borrow" some 100 low lead and put it in my bike, long story short my bike ran so much better on avgas I decided to "borrow" more, a week later I was replacing the top end on my bike because of burnt valves.