gasoline octane..

i have been hearing some guy's saying the older equipment should use the higher octane gas, is there any reasoning behind that?
years ago guy's used lead additives in their hotrods when leaded gas was no longer available, does anyone ad lead?

With few exceptions the opinion on this forum is no additives to gas. As to octane, I won't comment except to say that an answer either way always starts an argument.

I think the consensus was and always has been no additives are needed, and I dont use any other than a stabilizer in my fuel when I have to add some gas to finish cutting. On octane, I think the consensus was No, it doesnt need high octane unless youre working the snot out of it, and then its been ususally the 6cyl. that do.(Im meeting with a friend whos voluteered the use of his 706 gas, and a couple of others to be fair, and has the money, equipment and time to verify statements made about octane here, if for nothing more than my personal knowledge. I am going to post results later this week, but I can already hear the cooments that are going to be made.)

Octane # is it's ability to resist "pre-ignition"or pinging/knocking.So the higher the compression ratio the higher the octane you need.

Lead additive is not needed.........I cringe even calling it that, because it sure isn't tetraethyl lead. Previous commentary on octane is pretty much my opinion. I have all letter or F series tractors. They are get he same thing my car and truck gets: 89.

Tetraethyl lead was added to increase octane rating. Nothing else. If anyone tries to tell you anyting other than that, don't listen. all the F series tractors and the letter series tractors were designed to also run on distillate or kerosene. Neither had lead. Now the higher compression/performance 6 cylinder (or similar) engines require higher octane, but not lead.

do an internet search on tetraethyl lead, and read why it was added and what it does. Then you can reach your own conclusion. It will help you sort out the 100 different opinions you will find here.

Unless your older equipment is a Pratt & Whitney 1340 radial or a Franklin aircooled engine. Don't waste you $$$ on snake oil lead additives which contain no lead.
Ever notice that for many decades. Diesels, all fuel and propane engines have operated just fine without lead?
Ever notice that back in the days of lead. An engine with 100,000 miles was a smoking clanking wreck. Now with unleaded fuel that burns clean and doesn't leave deposits. A gasser with 300,000 miles is boringly common. And if opened up, it looks like an LP engine's internals.

As for octane requirements if you have a cranking pressure of 180-190 lbs then I would say you should think about high octane if you are going to work it. If you have cranking pressure of 125 lbs I would use regular.

Octane of gasoline is like progression in smokeless gun powder. The higher the octane or more progressive the powder is the slower it burns. Higher compression causes fuel to burn faster so we slow it down to arrive at the same approximate time frame of combustion as a lower compression engine with lower octane . Gun powder, the heavier the load, higher pressure so we slow it to control it. Very similar situation.

(quoted from post at 15:15:57 07/24/10) i have been hearing some guy's saying the older equipment should use the higher octane gas, is there any reasoning behind that?
years ago guy's used lead additives in their hotrods when leaded gas was no longer available, does anyone ad lead?

Click to expand...

The lead additives are lead substitutes, not actually lead. The reason for their introduction was not to raise the octane rating, as the tetraethyl lead was used for, but rather to act as a lubricant for the valve seats and faces.

By the time the tetraethyl lead was introduced, most engine design had progressed to the point where it's benefits for valve lubrication was minor. Early engines, mostly built before WWII, had valve seats that were just machines spots in the cast iron. These seats worn quite quickly, especially if valve rotators were added to help break up carbon deposits on the mating surfaces. The tetraethyl lead proved to be of some benefit for extending valve life in those engines.

(quoted from post at 00:51:17 07/25/10) Octane of gasoline is like progression in smokeless gun powder. The higher the octane or more progressive the powder is the slower it burns. Higher compression causes fuel to burn faster so we slow it down to arrive at the same approximate time frame of combustion as a lower compression engine with lower octane . Gun powder, the heavier the load, higher pressure so we slow it to control it. Very similar situation.

Click to expand...

That is the most concise explanation of why we use different octanes that I've seen on this board.

The "time frame" is basically 10 degrees ATDC. No matter what fuel is being used or what the engine speed is, combustion should be complete by about 10 degrees ATDC. Ignition timing is changed to achieve that goal.

I have to agree with Pete he has a handle on it.

There is a formula that shows the power that any fuel gives off when burned. The higher octane fuels tend to give off lower power numbers due to the way they work "slow".

"Spark knock" pre ignition , you need better fuel or the timing curve reset.

With high octane fuels more timing is required in the motor to get it threw and reep the benefits of it .

Based on this we have tried differnt fuels and timing curves on and in my "M" on the dyno.

Once the cylinder presure starts getting up over 160 or more then fuel is a issue.

In this case if it is a stock tractor then the octane is not needed and may actually hurt the performance.

So in short your good and don't worry.


The only thing that we all have to worry about is todays oil. They are taking more and more "zinc" out of it causing engine failure.

Will it effect our older toys , hard to say.

Do your homework on oils and there zinc content , this is becoming a bigger problem.

GM requires a special oil and or additive in the Corvette motors etc etc etc due to the roller cams wiping out do to not enough zinc in the oil made today.

Owen, I agree that Pete23 gave a really good example. However, the tetraehtyl lead (TEL) was not originally added as lubricant for the valve seats, the higher octane it produced in gasoline did 2 things: by raising the octane it reduced pre-ignition (knocking) and it reduced the heat of the combustion. Both of which would batter and erode valves. That is the reason for the hardened valve seats in unleaded heads, so they could run on lower octane fuels (stellite valve seats have been around even longer than TEL, as it came into use around 1916). Stellite valve seats were also added to "high end" engines. Increased compression and higher RPM engines require higher octane fuel. TEL was at the time, the most cost effective way to boost octane rating.

In fact, the lead "cleaners" 1,2-dibromoethane and 1,2-dichloroethane are added with TEL to clean the lead oxide out of the combustion chambers and valves. So I agree, the residual lead oxide would have lubricated the valve seats, but once again, that was not the original intent of the TEL. Early on, before the "cleaners" were added, the lead would build up on the valves and other parts of the engine, and were actually worse than carbon.

I am not trying to bust anyone's chops here, but the chemistry behind this is very specific and simple. Lot's of urban legend on why TEL was added, and what it did. most of those explanations are not completely correct, or flat out wrong. They have been passed from person to person over the years.

TEL was introduce into fuel in 1923.

If anyone is interested, here are 2 links:
[u:4a4afd1da3]Timeline of TEL: [/u:4a4afd1da3] http://www.google.com/search?q=tetr...mp;ct=title&resnum=11&ved=0CEEQ5wIwCg

[u:4a4afd1da3]History and chemistry[/u:4a4afd1da3] http://en.wikipedia.org/wiki/Tetraethyllead some of this one needs to be taken with with a grain of salt, but it gets most of it right.

James, right on!

Tom, you are correct as for the reason for the addition of TEL. If you will reread what I wrote, you will see that is what I stated.

What I was talking about is the reason that the additives where pushed after the removal of TEL from the fuels. Because the lubrication benefit of TEL was so minor at the time of it's removal, the use of lead substitutes have little or no benefit.

Owen, absolutely agree. Sorry if my reply seemed directed at you. I intended it more for the rest of the readers......probably could have done a better job of writing it.

No offense intended.