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At what RPM is peak efficiency (torque) for M?

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M.Rad.

05-26-2007 22:18:32

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I'm thinking of putting a tach on my M, so I can run it at it's optimum rpm for peak efficiency while pulling a disc or shredder. What rpm would that be? Currently it pulls an 8' disc (two sets in front two in back) easily at throttle setting "2" on the lever, in 4th gear. But I have no idea how fast that is (rpm) or how efficient.

Any help is appreciated!

Regards,
M.R.

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M.Rad.

05-28-2007 19:14:39

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Thanks again, guys. I alway avoid lugging any eng in reply to M.Rad., 05-26-2007 22:18:32

but I also didn"t want to over-rev the unit. The disc I was pulling had a very shallow "cup" (sorry for not using the correct nomenclature-I"m new to this), and even with two cinder blocks over each set of disks (8 total), and fully "angled", it still didn"t cut very deeply. Still, the old M was never even breathing hard.

As for the throttle lever, it"s the standard type with numbers cast on top aligning with a line on the support bracket. Numbered 0-6, I believe?

Regards,
M.R.

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M.Rad.

05-28-2007 19:13:17

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Thanks again, guys. I alway avoid lugging any eng in reply to M.Rad., 05-26-2007 22:18:32

As for the throttle lever, it"s the standard type with numbers cast on top aligning with a line on the support bracket. Numbered 0-6, I believe?

Regards,
M.R.

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Cedric

05-28-2007 04:09:16

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Re: At what RPM is peak efficiency (torque) for M? in reply to M.Rad., 05-26-2007 22:18:32

I have a 1971 reprint of the Blue Ribbon Service Manual for the H & 4 Series tractors which also includes the U-4 Power Unit. As part of the description for the Power Unit there is a graph showing performance curves. Maximum torque of 110 lb.ft. took place at 1200 rpm's at just over 25 hp. As agpilot suggested, the torque curve was fairly flat, ranging from 90 lb.ft. at 600 rpm, up to the maximum of 110 then back to 90 lb.ft. at 1800 rpm.
As far as I'm aware the U-4 Power Unit and H engines are identical so these figures should also be applicable to the H.

If you can get hold of a Blue Ribbon Manual for the M it should have the I-6 Power Unit in with similar information.

Hope this might be of some help. Sid.

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CNKS

05-27-2007 08:47:08

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Re: At what RPM is peak efficiency (torque) for M? in reply to M.Rad., 05-26-2007 22:18:32

Also, that disk is probably a little small for an M. WOT is 5+ mph in 4th. If you are running in 4th at part throttle, you need to put some weight on it or get a bigger disk. In any event, you do not want to lug the engine, regardless of rpm. I don't know what kind of throttle control you have, must be aftermarket, because the 2nd notch on the standard notched throttle is barely above idle. I have spent maybe a couple of thousand hours on an H with a 6 foot heavily weighted tandem disk in 3rd gear. That was all the H wanted, it would accelerate smoothly from a standing start to full speed in third without lugging -- that is the most important thing. If you feel that engine lugging, you are going to burn the valves, or worse, which will cost far more in repairs than the gas you save.

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CNKS

05-27-2007 08:33:45

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Re: At what RPM is peak efficiency (torque) for M? in reply to M.Rad., 05-26-2007 22:18:32

An older tractor like the M was designed to be run at full throttle for "normal" loads. For light duty such as pulling a hay rake, or cultivating, they can (must be for cultivating) throttled back. For a plow, disk or shredder that is sized to the tractor, full throttle. This is not necessarily true for modern tractors which can sometimes be shifted up and throttled back for lighter loads.

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agpilot

05-27-2007 10:58:34

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Re: At what RPM is peak efficiency (torque) for M? in reply to CNKS, 05-27-2007 08:33:45

Hello CNKS: With all due respect, I don't remember reading anything where IHC stated that the M engine was designed for full throttle. As a backup to this I'll point out that rated PTO RPM of 540 is obtained well below max engine RPM. Why did they not use full engine RPM power to the PTO? I can't recall all the books or manuals I've read years ago but I'll stay with my impression that the M and most other 4 cylinder Farmalls were designed with a fairly Flat torque curve from half to full RPM. Most non-turbo engines have a peak in torque about 70 percent max RPM. An earlier 425hp Corvette I had peaked torque at 5100 but Redline was 6400. I've read many of your posts and you have a very good knowledge of Farmall but I'll hold to staying with saying the M has a very usefull and relative flat output power from above half RPM to almost full RPM. Another place I can see flat output in most 4 cylinder classic Farmalls is in a tractor pull. They hang tuff untill engine RPM goes below about half. Then they fade faster. Most aircraft piston engines have published torque curves and fuel used vs power output etc for all comercial pilots to use. Pilots have to know this to plan a safe flight. If only we had this type of info on Farmalls like I've seen for low RPM non-turbo piston aircraft engines... Hopeing your having a great weekend... agpilot

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CNKS

05-27-2007 15:00:19

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Re: At what RPM is peak efficiency (torque) for M? in reply to agpilot, 05-27-2007 10:58:34

I think my point is, that those are not "modern" engines and most farmers, at least for tillage loaded them to the gills, as our H was -- therefore we had to use WOT to pull anything. And for what it's worth, my college machinery professor in the 50's, said to use WOT, we were always donated an IH tractor for that class. Aircraft engines are NOT the same -- I was a flight mechanic on the old C 54's in the early 60's. Sat between the pilot and copilot and did the prop and throttle settings during cruise -- none of my business during takeoff, we would crash with me working them. Max power only during takeoff, less than that during most climbs -- not the same thing as an old tractor engine. Torque and HP are both important, but those old tractors were run wide open except for cultivating, regardless of load.

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D Slater

05-27-2007 14:45:11

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Re: At what RPM is peak efficiency (torque) for M? in reply to agpilot, 05-27-2007 10:58:34

agpilot, I don't claim to be a expert on this subject so here is some things I know and others I think. On stock M the maximum no load RPM setting is 1595 to 1600 area,maximum full load RPM is 1450. The PTO speed is 537 RPM at 1450 RPM. The stock engines make there most torque between 900 and 1200 RPM and don't drop much down to 775 to full governed RPM. Under light loads at full throttle these engines are operating maybe 30 or 40% below what there maximum RPM would be if not governed. At maximum load the load keeps RPM down until it lightens enough for governor to close butterfly in carburetor some. Back in the days we used them for heavy tillage the throttles were locked wide open and left there. On light loads the same most times just because of the slow forth gear speed. Of coarse fuel consumption was not looked at as hard as now.

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agpilot

05-27-2007 06:08:20

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Re: At what RPM is peak efficiency (torque) for M? in reply to M.Rad., 05-26-2007 22:18:32

M.Rad: I would guess people like Guy Fay has seen engineering reports that show test results of where the best RPM is for any given load. Lacking that info, I'll add my 2 cents from what I've seen on low RPM aircraft engines. Most operate at 75 percent for an average load. Their best miles per gallon would likely be 50 to 60 percent max RPM with average load but your adding time to completion. A very heavy load would require at least 75 percent. With all that said, I'll refer back in my memory to the days when I sat on an MD or gas M all day and say that if it handles the load fairly well, without relying on the governor, at 75 percent RPM, your probably close to best efficiency. agpilot

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M.Rad.

05-27-2007 07:20:50

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Thanks Agpilot. Do you know what red lineq in reply to agpilot, 05-27-2007 06:08:20

Knowing that, I could calculate best "cruise". Also, do you know where I could find other info such as compression ratio, stock cranking psi, dyno graphs (if any exist), etc?

Regards,
M.R.

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