Fuel octane recommendation

This is old information from IH, but thought it may interest some with all the fuel postings going on. May take me a few posts.

lower part of same page.

This information was more for the 4 cylinder engines I think. I get confused with the different methods and numbers. Right or wrong, would the 87 Research Method recommended then be a lower octane than 87 posted at the pumps today?

This seems very relevant and easy to comprehend. Research octane is higher than The averaged numbers we find on most US and Canadian Pumps. Thus an 87 RON requirement is easy to meet with an 87 combined number. Jim

The current number is lower than the old number that included only the Research method. The current number is lower because it uses the average of the Research and Motor numbers. I added to the thread several pages back by now that the "new" method R+M/2 is 4-5 points lower than the Research method. BUT, other things being equal, in other words ignoring the improvement in todays gas over that of the 50's, research octane is about the same. TV says that the operators manual for the 706 says 93 octane (someone check that in their manual) -- that is the research number. Todays research number for 89 octane gas is also 93 maybe 94. Current 87 octane has an R number of 91 or 92. Motor will always be less than research, so the end result is that the current octane number posted on the pump is less that what would have been posted in the 50's -- if such a number was posted them. 93 octane on tdays pump would have an R number of 97 or 98.

And the 87 research number for the 4 cyl engines converts to 83 using the R+M/2 method. For todays 87 octane, the lowest you can buy except for high altitudes such as CO, is 91 as stated above.

Maybe I'm mixed up, but my thinking is that IH at that time recomended 87 octane gas using the research formula. If the motor formula was used the octane rating for the same gas would be lower. Wouldn't the octane rating on todays pumps now be a average of the two testing types? So the 87 on todays pumps should be lower than what the reseach octane # for the same gas would be. Or ROM 87 gas = a lower reading for the same gas using the other two methods . Or If rom was 87 the mom may be 77 or so, wouldn't that make RM2 on todays pumps 82? Is my thinking messed up?

If the 87 octane on the pages you posted were produced today, the R+M/2 currently in use would say about 83. So, the 87 on todays pumps is higher octane than the 87 octane recommended in 1958. The research number used in 1958 goes up to 91 or so due to todays higher octane regular gas. If the R octane was still 87, use of R+M/2 with a M of 77 as you stated would be 82. I don't know what the M rating was in 1958, though. I think I just said that today's gas is better than it was in 1958 -- I'm probably going to get in trouble. But as far as I'm concerned, it is. Unleaded gas burns cleaner than leaded, and the quality control is better than it was 50+ years ago.

You are correct, to get 87 today as an average, today's "research only" would have to be higher than the "research only" recommended in the book.

The upshot being that today's pump gas rating well exceeds what is required in the manual.

Good post! Interesting how the manual elaborates on difference and similarities between High Test and Regular.

I just used the 77 number as a example, but it would be make the RM2 lower than the 87 anyway.
I'm just after the facts, don't care who is right or wrong or if i'm wrong.

Good post. It is nice to see some actual data rather than a bunch of hearsay.

CNKS, great soil scientists think alike. :lol:

Now that is good . where did ya find that at???

In my opinion given without proof, I now think you can add 4 points to the octane posted on any pump and be close to the Research number recommended by IH. I was incorrect in the earlier thread because I was basing the R number of all grades of gas on 82 as an M number. Incorrect because as the R number goes up, the M number goes up too, by the same amount, I don't know.

Perhaps, but soil science doesn't have anything to do with gas or octane. In this case all my education does is to make me try to reason things out, and sometimes to question things that make no sense to me, which maybe I should have ignored.

Then WHY is it that most cars of today only run around a 8.5to 1 ????? plus all the computer controls ing. timing ?? I am by far a math major . And like someoine else posted the compression ration of the C263 and the C301 Stock when new . And like i said as far as i have knowen that as long as i have been playen with engines we have been on the research method till they started playen this numbers game with it . When this emission thing started the first thing that went down the tubes was compression ratio then cam timing was layed back 4-8 degrees carbs richened up and fuel milage went to the basement and horse power went into the cellar . Also answer me why we have this problem with over heating and detonation when everything that you can control is still there?? have you ever tryed hauling a load of grain with say a 77 I H 1600 load star with a 345 in it up and down our hill The 87 of today will not do it . Here again you have to move up to get the same performance . What i have said all along is that before 1975 reg gas at the pump at 90% of the stations was 95 octane ok yea it was the OLD Research rating .Also on these old 4-6 cylinder engines after 58 when they were new before they ate valves and had there heads milled down god only knows how many times now you got problems. Now the other problem i have with you directly is (1) you do not farm with your tractors (2) you do not work on them (3) you have never run into these problems . But you are the first to condemn me for given my advice . As to what i have found over the 25 years of fighting this problem . And if and extra 60 bucks a year on 300 gallon is tomuch to spend on you tractor to save and engine then you is really cheap even if i am wrong which i am not .

Fuel quality is of extreme importance in operating a farm tractor. I believe the sincerity of the The Tractor Vet in his insistance on 93 octane fuel. I respect his opinion. I believe the fuel delivered by the bulk distributors in his location was of poor quality control (especially from one source, maybe a particular brand or farm supplier, that had a desirable price. (I suspect it would not have gotten to 85 R+M/2) I have been around farmers with 6cyl gassers that have used "regular" gasoline in them from new without any detonation issues, and expected engine life. When the lead free fuels were introduced no changes were made. When alcohol was added, no changes. IH Oil with Low ash was used (or premium brand name diesel oil that had limited ash in its formula). A coked up engine with radical deposits in the chamber will be far more successful staying alive on 93, than 87 R+M/2 fuel.
I found this in tractor Data .com if it is relevant. Jim
Interntional Harvester C291

Fuel: gasoline

Cylinders: 6

Valves: -unknown-
Bore/Stroke: 3.75x4.39 inches [95 x 112 mm]

Displacement: 291 ci [4.8 L]

Cooling: liquid

Compression: 7.5:1

Rated RPMs: 2300

Dave, I didn't specifically answer your question, although you have probably figured it out by now. I think you meant "is the 87 octane research number recommended in 1958 lower than the one used for todays R+M/2 method?" The answer is yes. Todays 87 octane has a research number of about 91 vs the 1958 87. Also the R+M/2 which was not used in 1958 would have been about 83.

Old dealership stuff. Looking for something later than that info and on 6 cylinder gas but no luck so far. I agree with maybe for saftey going up a grade on gas for a engine operated under full load if its boarderline on octane needed. I would in mine if there was a doubt about the gas being god enough. When a checkup on stations and octane is run by inforcement once in a while around here, some have a lower octane than the # on the pump.

Tractor Vet, if you are talking to me -- I am not the first to question your octane numbers. I never understood from the first time you posted about needing 93 octane in 7.2-7.7 or so compression tractor engines. Then at some time it occurred to be that you were using the research method rather than the current R+M/2 method. There is a difference. As a compromise according to what I have read, 89 octane by the R+M/2 has a research number about 93, this probably varies some depending on who makes it. By the same token the current 93 octane by the R+M/2 has a research number of about 97 -- use it if you want. I was the first responder to a thread several months or maybe a year ago, not initiated by you when I said "I'm going to run 87 octane in my 460, regardless of what the experts say". I believe those were my exact words. You immediately tore into me with your usual statements about how ignorant I was and did not have your experience and had no clue what I was talking about. The thread went downhill from there, and you said you were leaving the forum and weren't coming back or something like that -- I went out to work on my tractors that you say I never work on, and when I came back the thread had gotten so bad that the administrator deleted it. You stayed away for a couple of months and came back. AND for your information I said I had a 460. The operators manual says to use 87 octane by the research method or 80 by the motor method, meaning that the R+M/2 method it was about 83.5 and hasn't even been sold in the recent or not so recent past. I will agree that on the 706-up tractors that have excess carbon in them, that a person needs to be careful with them, and perhaps they may need a higher octane number than the manual says. As the last page that Dave Slater posted says, sometimes there is damage when you can't hear detonation, and there are other factors involved. There are others on this forum who insist they have run 87 for years without a problem. Those are the ones who do not abuse their tractors. I get the feeling, although without proof, that many of the tractors you have worked on and correctly or incorrectly assumed that the wear you saw was caused by low octane were abused. Appears that your area is full of hills. I live in flat country and the soils are fairly uniform. My conclusion is that if you take care of your tractor, and don't overload it, that the octane number posted in the manual is fine.

Tell ya what here do you have skypes??? If Then why don't we get together on that. And i will show you just what happens when you get the wrong gas in one and i don't care if you run a 460 it can happen to them as well . I fought the same thing on a friends 460 that was bought new on the farm in 57 and it has had the head off it so many time for burnt valves over the years and each time that head was milled because of warpage. So the stock compression ratio is long gone out the window . It would not even pull a half loaded manure spreader back up the hill with out tiren to seize up . And you ignore when i try and tell you that reg gas was 95 Research when they were built . The 93 is the min. on a stock engine with forged pistons . NOW we have cast pistons cast will not take the heat and dissipate it like a forged will down to the skirt and to the walls .If and when we can get together i will make a point of getting the lab report and read it to you . Yes we have hills over here and some of them will put a pucker factor in your shorts . I have shelled corn on a couple side hills that you could only shell one way and that was with the cab door on the up hill side and only with a half full bin and you drove it half in the cab and half standing outside the cab so IF she started to go over you had a small chance to jump for it. Or had a 4 row corn planted shove you side ways while turning on the head land . It gets steeper south of me .

What are skypes?? Whatever they are it is spelled wrong. And I'm not going to drive 800? miles to look at a lab report, or a damaged engine. You live in a severe area, extremely hard on engines, probably including diesels. But, my point is that one size does not fit all. You continue to post what you believe, I will post what I believe -- BUT I refuse to participate in any further direct discussions with you, they are fruitless. If you want to think you have won, so be it -- but you haven't. Bye!

Just my $0.02 worth. I work as a tech in a new car dealership. I can't recall any of our vehicles running only 8.5 compression. Most of them are in the 9.5 to 11.5:1 range and recommend 87 octane. These modern engines also put out up to 400+ HP. Even the 4 cyl can get close to 300 HP with the factory turbo. Of course they also use variable valve timing and ignition timing to control detonation. I also remember detonation issues on cars of the mid 70s through the mid to late 80s because they were trying to raise temps and lean out mixtures to reduce emissions. Those things would "ping" with 8:1 compression on 87 octane and put out 110 HP with a 350 V-8. Anyway I'll keep running 87 in my M's since I don't use them that hard anyway and haven't had any problem yet.