Fuel quality and octane level?

I just read the thread about E85.
In the past, a person or two has reccommended using high ocatane fuels in the older tractors because the regular fuel of the 50s and 60s had a higher octane rating than todays reg. fuel.
What is it about an engine that will determine if you need to use regular or premimuim fuel?
Compression ratio?
Cam shaft?
Distributor timing.
These older tractor engines are not very sophicated and I don't see why they would need to be run on High octane fuels. I really am hoping to learn a few things about this.
Steve

Well maybe by todays standards they are not BUT for there day they were the latest and greatest . And they were designed around the fuel of the day. Now and old M may GET by with it playing around But if you put her back to work and i mean work you will find out what happens . IF it has been upgraded with higher compression pistons and a better high compression head plus just how many times has the head been milled down over the years and like you said timing that new low grade gas is going to burn way hotter and on the CAST PISTONS that they sell today the pistons can not get rid of the extra heat that the 87 and 89 octane makes and the pistons will start to swell and guild .Then ya get into the higher RPM 4 cylinder and 6 bangers and it get worse . . All this newer gas is for cars and light trucks that just move your donkey down the road . Ya ok you haul your toys behind pick ups they still are not working as hard as a tractor in the field pulling a plow or a disk .Just how many of you guys ever spent 10-12 hours on a gas tractor plowing and as the sun sets the glow of the manifold and the muffler is a cherry redand there is a half foot of flame standing out the pipe. .The higher cotane burns longer and cooler and makes all the difference .

Most gas tractors were built for 70 octane, stock.

E85/any alcohol, is wonderful- and will have more octane. I have used alcohol for 34 years, very sucessfully. Biodeisel for 18 years.

In terms of IC engine theory, you want to avoid a knock event.

Knock is a point where the air/fuel mixture becomes unstable and explodes and releases a concentrated bit of heat. Normal combustion can be thought of as a smooth-flowing "ghost" that "sweeps" thru the chamber.

Main factors that affect knock are octane rating of fuel, how much oil is being consumed (oil has a very low octane rating...80 or below, tampering with the fuel's rating), the compression ratio, spark advance, and any "hot spots" in the combustion chamber ala a "hot" spark plug. Air density (for charging), air temperature, and relative humidity all make a difference.

You can think of knock conceptually as sandblasting your fingertip. It gets "hot" and one time doesn't cause any permanent damage. But if you did this 15 times per second (@ 1800 rpms for example, the crank rolls over at 30x per second and 15 of those are "power" strokes or combustion events), the heat would build up quickly...and a piston that can't get rid of that heat will eventually become aluminum gravel. Sharp edges on a piston for valve reliefs are an area it is difficult to remove heat from quickly and so are at greater risk.

My personal thoughts are that as long as you are not knocking audibly, then 87 octane is fine. Tetraethyl lead of days gone by did wonders for very inexpensively raising the octane rating of gasoline. The Farmall/IHC 4-cyl letter-series engines I've dealt with are all "low compression" in relative terms. The 6-cyl 221cid I just got has a 7.2:1 CR which is considerably more.

As TractorVet says, the duty cycle is important...if you are going to do your own Nebraska testing day in and day out you might want to think about premium fuel. All others I would personally recommend using 87 octane.

SDE,
The old octane ratings actually compare very favorably with the new method (R+M/2). Typically the Research octane is 10 points higher than Motor octane and was the number used in the days of our tractors. My DC Case manual calls for fuel no lower than 65 Research octane. So 65+55/2 would equal 60 octane in todays fuel.

So are any of the "octane boosters" any good or are they just snake oil? My only option around here would be to buy 100LL av gas and mix. Speaking of mixing, is it a simple ratio (half gallon 100 plus half gallon 85 equals one gallon of 94 octane) or more complicated than that?

Thanks

Best read up on what they require for fuel . And like i said the old M's over the years with the upgrades are no longer a low compression engine as every farmer out there never had enough horse power and the days of the distillate engines are long gone and with that came the fire crater pistons the high dome the lower CC heads and on and on . Even the old gas powered semi's from back in them days HAD TO RUN hightest gas . Way back in 63 i started driven a semi , it was a B 60 Mack with a big 6 cylinder gas engine and when i put gas in it you had to run the hightest and it was 105 octane same gas i ran in my 56 ford with the hopped up 292 with the 312 heads and iski cam with two 4bbl holley bird cage carbs and the mallory dual point dist. The gas that was brought to the farms was now get this 95 octane as i remember the stickers on the pumps as at my uncles farm there was tractor gas and it was 95 and there was the gas we ran in the old semi's that he started out with before the BIG trucks arrive that had the massive 8-71 detroit 318's . The old Ford F 1000 with the 534 V8 gas and the dodge 900 with the 413 they needed the 105 . In the late summer of 64 i started building my new car engine from a bare block and when done with that one she would run on the 105 but not like it would on the Sunoco 260. And also back then the pistons used were FORGED pistons in tractors and working engines and getty up and go fast engines. Now today we get cheap cast pistons and they do not like heat . I have seen many times what this new 87 octane gas will do to a working gas farm tractor . So it is like this you do what you want and when the day comes and you score 3- to all 6 pistons or you have a China syndrome in your engine and standing there wondering why this happened then just look back and what was in your tank. I see it on here all the time about my spark plugs keep fouling why . Well you will have plug problems more on the 87 compared to the 93 .

Vet---what do you think the loss of lead in fuel has done?? Back in the days that lead was in gasoline, the fuel actually had a red color to it. Gas nowdays is clear as water. What is your opinion of lead substitutes for adding to gas?? Mostly "top oil"??

Agreed. The older gas engines from the 1950s run with very low compression ratios. 87 octane will cover their needs without knock or excessive heat easily. As pointed out by Gary current octane ratings would have measured several points higher back in the 1950s and 1960s.

http://www.faqs.org/faqs/autos/gasoline-faq/part3/preamble.html

If you are getting engine knock with 87 octane on a engine with less that 8.5:1 compression ratio you have a problem - and it sure **** aint the fuel. Its only when you get up to 9:4 or higher that octane becomes an issue (with pump fuel) - and usually only with mechanical variable ignition timing.

The Super H in 1952 only had a compression ratio of 6.1:1 and the Farmall 450 only had 7:1 compression ratio - well within the operating range of current 87 octane fuel. Running 91 octane fuel in them is a waste of money.

I don't know anything about combustion theory and I only own one tractor, a 1966 140 that my old man bought when I was 14. When they got rid of the lead, she started to knock, but only when bushhogging thick grass uphill on a hot day. I hate knock--and after giving up on lead additives (made no difference), I switched up to Premium, no knock. She will bog down, but she won't knock. Mid-range or Plus, also no knock. So I have stuck with Plus for the past twenty years. Just one man's experience with one tractor. I have always gone by the rule that the lowest grade that doesn't knock is what you need, any more is wasteful. I guess turbos are different, but I don't own any.

Well way back in my time ya know when the dinosaurs roamed the roads along with land yachts cruised the roads Amaco had unleaded gas and it ran well no valve problems no ing. knock . And the snake oil in the bottle is just that. Myself and 4 of my close friends all run farmall gas tractors and since we have all gone to the 93 octane gas even the old M's run better less plug fouling they don't fall off as fast under load . As for the valves and seats heck I H has always used stelite valves and seats on the exhaust . So no worry over that end of it. The biggest worry on a I H gasser is the oil and here it is a must to use the LOW ASH . IF you have a valve problem then you are not using low ash oil.

Thank you for the replies. In the future, when I make the tractor work hard I will use the better fuel. I noticed the manifold and the muffler were quite hot last year when I pulled a digger for 4 continuous hours. I am planning on playing farmer again this spring. Otherwise my tractor is just a toy that puts a smile on my face.
(when things go well)
Steve

The octane rating is a measure of resistance to ignition, basically the higher the octane, the hotter the flash point. The higher flash point is needed with higher compression so that the fuel doesn't detonate from the heat from compression and from the walls of the chamber. The knocking you hear is actually the engine trying to run like a diesel, through compression ignition, instead of spark ignition. It's trying to kick the crank over backwards because it's firing early. I think retarding the timing can help eliminate detonation but you'd have to check up on that.