Unleaded versus leaded gas

[John Lapic]

Years ago, there was no such thing as unleaded gas. Now, we can't find it. Are there any performance issues using unleaded gas in older motors? Would adding lead additives to oil/gas mixtures improve performance and motor life?

 

[DJ]

Re: Unleaded versus leaded gas

Lead was added to coat valves in four cycle engines. Lead does not do anything for two cycle engines. Unleaded is acttually better for them.

You also do not need premium. 87 octane is fine.

 

[John Lapic]

Re: Unleaded versus leaded gas

DJ - thanks for the quick reply and the advice. Good to know spending more on premium gas will not do any good.

 

[jay_merrill]

Re: Unleaded versus leaded gas

As DJ said, the issue of leaded v. unleaaded fuel is an issue for 4 cycle engines, not 2 cycle. If you have an older inboard or I/O, you could possibly have some issues with the valves in the motor because the lead acted as a lubricant for the valve seats. This is generally true of motors built prior to 1974. If the motor has been rebuilt, however, hardened valves may have been installed and things could be fine.

The only 4 stroke outboard that I can think of which could be affected, is the Homelite 55hp 4 stroke.

 

[JB]

Re: Unleaded versus leaded gas

Actually, back in the days of leaded gas many outboard manuals recommended using "white" gas.

Amoco sold an unleaded gas that was clear and about 80 octane. They called it white gas and it was "the" gas to use in outboards and gasoline powered lamps and other appliances.

 

[JCF350]

Re: Unleaded versus leaded gas

If the motor has been rebuilt, however, hardened valve seats may have been installed and things could be fine.

 

[Texasmark]

Re: Unleaded versus leaded gas

Hey JB. I remember those days. Never figured out how Amoco did that; white gas in a leaded market, valve erosion potential with no lead....what'd they call it "Tetraethyl Lead"?

Don't remember what I ran in my rigs then. Had a few Amoco stations around So. Texas, but not that many.

Mark

 

[SpinnerBait_Nut]

Re: Unleaded versus leaded gas

Mercury says for best performance out of my ProMax, use premium.
There is something they do to them so you can run the lower grade, but don't know what it is.

 

[JCF350]

Re: Unleaded versus leaded gas

Hey JB. I remember those days. Never figured out how Amoco did that; white gas in a leaded market, valve erosion potential with no lead....what'd they call it "Tetraethyl Lead"?

Don't remember what I ran in my rigs then. Had a few Amoco stations around So. Texas, but not that many.

Mark

Yep,
The damaged caused was from the unhardened seat material sticking to the valve.

Had to stay away from Amoco's with the motorcycles back then, made them ping like crazy.

 

[JB]

Re: Unleaded versus leaded gas

I think the white gas was originally intended for older, very low compression engines, yard tools, lanterns, outboards, etc. Uncle Tom used it in his '34 Ford with no problem.

Tetraethyl lead was used mainly to increase the knock resistance in gas (octane number). The lubrication of valve seats was serendipity and allowed makers to use unhardened valve seats.

I ruined the valves and seats in my Mom's '46 Ford by burning aviation (unleaded) 115/145 in it. I got the avgas free from my employer and thought it would make the little flathead V8 roar. Wrong.

 

[jay_merrill]

Re: Unleaded versus leaded gas

Actually, 115/145 is a highly leaded fuel. The avgas that is sold today is called 100LL and that is somewhat of a misnomer, because it is only low lead in comparison to older aviation gasolines.

In the days when there were aircraft engines that required higher octanes (and hence, more lead content), there were basically three grades of avgas sold - 80/87, 100/130 and 115/145. the 80/87 had a maximum lead content limit of .5 grams per gallon, for 100/130 there was no limit but it generally contained about 3 grams per gallon, and 115/145 also had no limit but usually contained about 4 - 5 grams per gallon. Some 115/145 even had up to 6 grams per gallon.

When I was flying SAR in the Coast Guard, we were still operating a piston engine aircraft (Grumman Albatross) that had engines of 1820 cubic inch displacement. They required a fuel grade of at least 100/130 but we used to run 115/145 in them. A few of my fellow airmen used to think it was a good idea to steal the stuff by making a nozzle adapter to reduce the diameter of the larger fuel nozzle on the refueling trucks. They would then sneak out in the middle of the night to the back of the hangers, where the fuel trucks were parked, and let fuel gravity feed into their tanks by simply squeezing the nozzle trigger on the truck's hose. The joke was eventually in them though, because the Guard got hip to what they were doing and started watching the trucks. It was always amusing to see an airman trying to explain why he had a tank full of purple gasoline!

I am not a petroleum engineer but I would guess that 115/145 burns hotter than regular gasoline so that is probably why you damaged your engine.

 

[JCF350]

Re: Unleaded versus leaded gas

I am not a petroleum engineer but I would guess that 115/145 burns hotter than regular gasoline so that is probably why you damaged your engine.

Don't know about temperature wise but the higher octane fuels do burn slower
in an engine of the same compression ratio's (so it would seem they would be cooler?). Thats why you get pinging when burning low octane fuel in a high compression engine.

 

[DJ]

Re: Unleaded versus leaded gas

It was always amusing to see an airman trying to explain why he had a tank full of purple gasoline!

I am not a petroleum engineer but I would guess that 115/145 burns hotter than regular gasoline so that is probably why you damaged your engine.

It's also amusing to watch truckers try to explain away red diesel in their tanks.

Higher octane means a SLOWER burn. As far as temperature, I would have to say it is less. Those enormous piston aircraft engines were known for needing octane. They would rattle something fierce without it.

 

[jay_merrill]

Re: Unleaded versus leaded gas

You guys are probably exactly right on the burn. That would also explain "burnt" valves because the duration of the cam for the exhaust cycle (open exhaust vakves) would be designed for the faster burning fuel. I would think that a slower fuel would still be "burning" as the exhaust valve opens.

PS: Heck DJ, they rattled alot anyway! We used to wear the David Clark type headsets that looked like oval hockey pucs, because they cut the noise considerably. Imagine 3640 cubic inches of piston power with no muffler system and pipes that were only a couple of feet long at the most! We also used to say that if an engine wasn't leaking oil, there probably wasn't any in it! We actually used to flight plan about a gallon an hour of consumption per engine and the things used 50 weight oil!

 

[Texasmark]

Re: Unleaded versus leaded gas

Very interesting nostalgia. I also recall back then that the valves had to be redone at 45,000 and the engine was crap at 100,000.

We had some low octane white gas when I was a kid also. Had it in one of those overhead tanks where you crank up what you want and let gravity deliver it to your tank.

Anybody run flathead Fords and put penny's in the heat riser ports to make the engines run cold and make the Smitty's louder? Grin. That has been a long time ago.

Then there's the time the neighborhood boys (I was the ringleader) overhauled the flathead V8 in the neighbor's '49 Merc and we assembled it DRY. Quite another story.

Mark

 

[Texasmark]

Re: Unleaded versus leaded gas

Then there was daddy's '56 Chev station wagon that I would get going to about 40 mph, turn the key off till it got down to about 30 and turned the key back on. That was great sport till one day I blew the muffler off and had to explain "that I couldn't imagine" why his muffler failed. Ha!

 

[SuperNova]

Re: Unleaded versus leaded gas

My understanding is octane is a measurement of fuel volatility with higher numbers being more stable and therefore more resistant to detonation and pre-ignition. The downside is that they burn more slowly and develop less total pressure. And on a high revving engine, some of the fuel ends up burning in the exhaust mainfold at higher rpm. Lead was used in the early days because of technolgy. It was the only thing they could get to stay suspended in the fuel. With the advent of better tech and the knowledge that lead was poisonous (which I personally believe they knew all along) they came up with less poisonous compounds to replace lead. I personally do not believe the whole "unleaded valve recession" theory and I have never seen it proven in even the slightest fashion. I used to work in a cylinder head specialty shop where we did rebuilds as well as custom work for high-performance applictions ranging from circle track dirt cars to big block drag boat--I even worked on the Accel Performance drag boat. I never saw one case of valse or seat recession attributed to lack of lead in the fuel. However, we sold a lot of hardened seat jobs and laughed all the way to the bank. There was nothing wrong with doing an upgrade--and it IS a good upgrade--just it wasn't as necessary as people believed.
--
Stan

 

[MikDee]

Re: Unleaded versus leaded gas

Then there was daddy's '56 Chev station wagon that I would get going to about 40 mph, turn the key off till it got down to about 30 and turned the key back on. That was great sport till one day I blew the muffler off and had to explain "that I couldn't imagine" why his muffler failed. Ha!

Been there, Done that

In fact many yrs ago, I had a Smittiy's glasspack on a 56' Olds 88 I had, man that sounded so good!

Later on I put a Smitty's steelpack on a 60' Chevy 2dr Biscayne stick shift, that I had just put a rebuilt 283 V8 with a mild cam in. It made that sound real sweet going thru the gears.

 

[jay_merrill]

Re: Unleaded versus leaded gas

One of the first cars I ever drove was my grandaddy's '51 Lincoln Mercury. Big ole flathead engine, three speed and an "overdrive" that was engaged with a handle that look like a parking brake handle. He was still driving it when he died on the early 1980s.

 

[Hoss the Hermit]

Re: Unleaded versus leaded gas

Lincoln Mercury??