Displacement/engine speed/HP

When evaluating different tractors, I notice that some of the newer tractors have smaller engine displacements but higher rated engine speed, giving the same HP rating as other new tractors and some of the older tractors. What are the implications/advantages of displacement with lower speed vs. small, high speed engines? Is it newer technology that allows the new tractors to run at higher speeds, and is there a wear/durability difference?

Opinions are much appreciated.

Torque is brute twisting power applied to a shaft. Horsepower is a meaasure of work and calculations involve time, distance, and mass. They're two different issues.

Long ago, in a tech tng class, I asked a Chrysler tng rep why the short stroke and elevated RPM. Answer came back as "lowered emissions". Bravo sierra!

Do some calculator work on cylinder bore vs crankshaft stroke. It is almost a no-brainer! The long stroke hemi-head engine wins every time. Their smog problems were from the long overlap camshaft grind and the slovenly carburetion needed to make their powerful hemi work.

Look back thru the 70's & early 80's Japanese engine specs and you'll see a bunch of long stroke vs bore hemi head engines in the high MPG and low emissions category.

Very interesting is that the short stroke design has a higher "cold wall quench" ratio and theoretically higher exhaust emissions problem.

What needs to be addressed is that engine power boils down to how much fuel and air can be burned in a unit of time. Run up the RPM and the BTU's used go up accordingly. But, efficiency goes to pot and exhaust emissions go up. A wonderful opportunity to add on lots of "value added" smog equipment...

Modern computer control technology has made it possible to do miracles with the spark ignition IC engine. But, in 1980 I was doing carefully controlled 2 way road test runs with a 1920 Model T Ford and getting 28 - 32 MPG and extremely low exhaust emissions.

Looking forward to more discussion on all this. "Three pedals and a lever", IHank

Most tractors with gasoline engines in the 30 - 50 HP range operate at about 2200 to 2600 rpm and run about 6.5 to 7.5:1 compression.

The flame travel is so fast at these low RPM's that that pre-detonation is not uncommon. One of my several tractors is a John Deere 1020. When I plow or heavily load it, I get the ping from it. When I know I'm going to lug it hard for a long duration I'll use premium gas or throw in a few mothballs (mothballs are made from a close cousin of the benzene and toluene family (unsaturated hexagonal ringed hydrocarbon) which is a component in Turbo Blue Racing Gas) that I keep in the garage to raise the octane.

Automobiles usually are rated at about 4000 - 5000 RPM for the advertised horsepower.

If you would turn up the governors on the tractors to allow the HP to be generated at higher RPM's as was described in the Farmall H story, you could get more power from them. This would be limited somewhat by the intake and exhaust passages and the shape on the camshaft lobes. These will be signifcant restrictions if someone wanted to increase HP more than 50% or so.

The reason that tractor engines endure so well is because the more massive construction of the block, crankshaft and rods. The flip side is that these engines probably wouldn't hold together long at a doubled RPM due to insufficent balancing and low pressure oiling. Due to the high circumferential speed of the bearings at higher RPM's, high pressure oiling is needed to maintain a film of lubricant between the sliding surfaces.

I've seen race engines get trashed in a few seconds after losing oil pressure. Spun bearings is the least, seized engines and thrown rods are the worst.

Chevy small blocks have endured over the years running at high RPM's because they comparitively run smaller rod and main journal diameters which minimizes the circumferential speed between the bearings and the crankshaft journal surfaces.

One of the main ingredients of race engines is a high pressure/high volume oil pump to provide a film of oil to float the bearings on.

Ken McWilliams
Dayton, OH

Thanks for the educational comments. It was interesting to hear that you use mothballs in your tank. In addition to being an old tractor buff, I have a Ph.D. in chemistry (unfortunately, playing with old tractors doesn't pay any bills, so I have a real day job), and I know that mothballs are paradichlorobenzene, as you say a relative of benzene and toluene. I would think that you would get deposits or enhanced corrosion of the exhaust system from using the chlorinated compound, over another benzene derivative. When mothballs burn, you generate hydrochloric acid (muriatic acid), which is extremely corrosive.

Just my two cents worth.

I don't use it often.

The HCl will be more corrosive to the aluminum pistons than to the steel and iron.

I reality, a few salts dissolved in water condensate will set up a electolytic cell in a cylinder and form galvanic corrosion to a greater extent. This is what most destroys engines when not put to use.

I tore apart a CASE engine 2 years ago that was seized. It took about 45 - 60 minutes per piston to break the rings out of the piston grooves and clean them. The white powder filled all the gaps.

Ken McWilliams
Dayton, OH

The old tractor engines, like the ones in my Farmall H, M, and SM have lots of torque, have lasted a long time, and work all day without complaint. Like your 400, they are excellent examples of "high-tech" for their day, considering the basic design was laid down in the 1930's! Look at automotive engines of that day, and you will see some of the same characteristics. The high compression high revving engines didn't start to come along in large numbers until the Olds/Cadillac V8 engines of about 1949 and the Chevy V8 of '55. Sure, there were other engines that had their niche, but these two set some major benchmarks.

It's important to remember that most of the "old" tractors we like so well had only 5 or 6 forward speeds; some had only 4, or even 3! If you don't have lots of gears to choose from, or the ability to shift-on-the-go, you'd BETTER have an engine with lots of torque, and the easy way to get that is LOTS of cubic inches, and preferably with a LONG stroke.

With the benefit of modern lubricants, even with a heavy work schedule, many of these old engines have outlasted their engineer's expectations. No engineer today would be permitted to design an engine (or tractor) with the "extra" strength, material, and longevity that was put into ANY of the major tractor brands of the 40's and 50's. The corporate "bean counters" insist on the most comptetive "bottom line" on the financial report that can be obtained, so engines are lighter, rev higher, and work harder.

It's a testament to the ability of the engineers at Ford, AC, Oliver, MM, IH, Deere, Massey, Case, and others that these tractors are still working the way they are. A tractor produced in the mid-40's followed the advent of really successful tractors by only 20-25 years, and they're still running (and WORKING) 50-55 years later! You won't find that too often in automobiles, trucks, trains, planes, or industrial machinery!

The new ones probably won't last as long, but they weren't really designed with that goal in mind. We live in a pretty much "disposable" society. Empty the can...throw it away.

My Father has often related to me the story of a conversation he had with another expectant father on the night I was born, in June of 1944. The other man asked what he did for a living, and my Dad told him he was a farmer. When asked if he had a tractor, Dad told him he had a Farmall H, purchased in September of 1943. The man asked if he liked it, and Dad gave him a rave revue!

The man then told Dad that he had been an IH engineer who worked on the development of the H and M models. According to him, field tests of the early H prototype indicated that it could not perform with a 2-plow load at the same level as an M with a 3-plow load. The quick-fix was to turn up the rpms of the H to enable it to perform as planned. He and a couple of other engineers wanted to do a re-design of the H engine and give it more cubic inches, leaving the rpms alone. This plan was turned down in the interest of getting the thing into production, and as a result, the H turns at a faster speed.

Engineers in those days operated with pencil, sliderule, and intuition. Those tractors were built from inspiration, not a computer program.

It's tempting to say that smaller is less durable, but about the only way you can really do that is to assume that the quality and technology level of what you're comparing is the same.

That said, it's usually seemed to me that the slower running engines lug better than the faster running ones.

The rub is in the "all else being equal" part. If one were to design an engine to develop the same horsepower at a given RPM as a 50-year old tractor engine, the new design would likely be quite a bit smaller and last at least as well.

If you're comparing current designs, then the "all else being equal" can be met and the rule will hold up reasonably well.

Another thing to keep in mind is the intended use of the engine. If it's used in a car, it can be designed to have a much higher HP rating than if it's used in a tractor. The reason is that in the car, the engine will rarely be anywhere near it's rated HP while it will normally operate much nearer the rated HP if used in a tractor.

A tractor, OTOH, is much more likely to spend hours with the throttle set at PTO-rated RPM, cranking out near-maximum horsepower, while plowing/disking or whatever. Therefore, the engine must be mechanically much more rugged.

My 32 year old tractor engine still runs like new. I wonder how many of these newer, smaller engines will be running 32 years from now!

Dean

The choice I was considering was between a Long tractor and a Kubota/NH/JD new tractor. The three majors have similar sized engines in the 38-42 HP class, about 134 cubic inches. The Long, in their 45 HP tractor, has a 195 ci engine, quite a difference.