HP needed to haul one ton

I read an article tonight giving MFG specs for an articulated haul truck that got me to thinking about the discussion on here awhile back. It began with me talking about my 55 and how fast I had had it running and wound up getting into a big discussion centered around HP, gearing, etc. The idea was put out that you could run a car at highway speeds with a small engine given the right gearing but the "majority" replied that it was impossible for various reasons.

For those that replied that it was impossible to get a "full sized" vehicle to a "highway speed" with a small engine, even with the proper gearing, I have these specs for you. The vehicle in question here is a Doosan Moxy MT41, or what is typically called an Artic or articulated haul truck, something that you see on construction sites all of the time. This truck has an 82,010 payload capacity and is driven with a 444HP Scania diesel engine and an automatic transmission with 6 fwd and 3 reverse gears. While it"s top speed is nowhere close to 55 it is well within what could be considered a typical vehicle"s speed with a top end of 32.9 MPH in high gear. Now, here is the interesting part. The article goes on to state that this particular truck has what is considered a "high" HP to ton ratio of 6.38 HP per ton of load.

Given this rating, any way you look at it, no matter what the ultimate HP of the engine, the HP per ton needed to move that 2000 lbs will never be greater than 6.38. Sooo, given those specs it just goes to show what was origionally said is true, given the proper gearing a small engine can indeed take a typical vehicle to a "highway" speed with the proper gearing. In other words given the right gearing you could easily get a 2000 lb car to 32.9 MPH using just 6.38 HP and the proper gearing. If this were not so then how do you explain this vehicle being able to take a 82,010 lb payload over 30 MPH using just 6.38 HP per ton....Remember, these are mfg specs on a production machine, not just something hypothetical like the numbers being thrown out before stating it was impossible.........

Well I guess if you consider 32.9 MPH highway speed then you may be correct. However, a lot of states, if not all, have a min highway speed of 35 MPH, which by law, makes your statement false. At least in the states with min speeds of >32.9 MPH.

Also Im not sure that there is a linear correlation. In other words if you took 444 1HP motors would the output power be the same as 1 444HP motor? I believe not because of several reasons, such as coefficient of friction, variations in timing, etc.

Don't know if Im right or wrong but its something to think about.

I can tell you from past experience...Toyota Corolla from the 1976-1978 era would take about 8.88 HP to move it down the road at 55MPH on a level road. Bear in mind there is frictional losses with drive train, tires, etc. and of course airflow dynamics play a big part. In order to provide fuel mileage and emission checks on a chassis dyno, the only way I could duplicate similar conditions on the dyno was to load it to 8 HP @ 55 MPH. Later on while visiting Toyota's emission lab I found out they dialed in 8.88 HP @ 55 MPH to perform Federally Mandated emission testing.

You didn't say how long it takes to accelerate that 40 ton payload to 30 mph. Top speed in any vehicle, be it car, truck, boat, ship or airplane, will NEVER exceed the point where friction exceeds available horsepower. Ore freighters carry enormous loads with relatively little horsepower because they operate at speeds where there is very little water and wind resistance.

I'll repeat what I said earlier: If you say you pushed your '55 at over 150 mph, then I believe you. But you got to that speed because you turned up the horsepower on the engine, not because of tall gearing.

Another example: airplanes. Take for example a Bellanca Decathalon with a 180 HP engine and constant-speed (variable pitch) prop. A very similar engine and propeller combination is used on certain Mooneys. Since the constant-speed prop gives both aircraft the ability to run at any "gearing" they choose, they should both capable of going 200 mph. Not so: while the Mooney is capable of close to 200 mph, the Decathalon can't go much over 100. Why? Because the Decathalon has a lot of stuff hanging out in the breeze, just like your '55.

Ok lets try a simple expiriment.

1 say you can walk at 3 miles/hr

2 same gearing you can run at say 5 mph

3 change the gearing add stilts and you sould be able to run at 10 mph.

higher gearing double the length of your legs you run faster?

You have neglected to take coefficient of friction /drag into your equasion.
The faster you go the harder you have to push to get thru the wall of air around us.

Wayne:

You are ignoring aerodynamic drag, which is inconsequential at the speeds achieved by off road construction machines.

Aerodynamic drag is an exponential function. It increases at an increasing rate as speed increases and is nearly always the factor limiting the top speed of race cars and aircraft. It is a basic law of physics that cannot be circumvented.

If you have spent much time around drag racers, you have no doubt heard the conventional wisdom that "torque produces a low ET (acceleration) and HP produces a high trap speed." Aerodynamic drag is the reason for the latter.

There is no way that 300 HP (or even 400) will push a 55 Chevrolet to 155 MPH absent a good downsloap and tornado.

Dean

Hang in there Wayne, just poking at you with my Honda story. If your '55 will go 100mph in high gear, you stop, pull off half of the plug wires and now it will ony go 52 mph, what happened? The gearing hasn't changed? I've owned GTOs, R/T Chargers, big block SS Chevelles, Corvettes, Camaros, R/T Challengers, RoadRunners, GTX's, Mustangs, 455 TransAm, 'Cudas, Firebirds, most of them were 4-spd, and most of them got driven hard. Probably the fastest on the top end was a '71 RoadRunner, 440 six barrel, four speed, manual steering and brakes.

You're way off again Wayne. The hp you need to move on the flat is based on the aerodynamics mostly so the frontal area and the coefficient of drag. The rolling resistance and other frictions are the next biggest factors.

If you throw in a hill, then the weight matters if you want to maintain a certain speed.

I would imagine that just like the big mine trucks, the articulated trucks are limited to lower gears and speeds when loaded and it takes a lot of HP/torque to get them moving from a stand still. The 32.9 mph max. speed would be with an empty truck returning for another load. Dave

If you doubled the length of your legs wouldn't that use more power to drive them decreasing your speed on hills ?

Ok so run some numbers and explain a 100car freight trains speed, HP and amount of fuel per ton per mile?
It's all about aerodynamics, inertia, HP and rolling friction..
Most mph dreamers failed or dropped out of math/physics class. And never heard tell of drag increasing by the square of velocity.

Exactly why I said (Experiment).

Just thought it made as much sense as "higher gearing".

Might be fun going down hill too.

Back when steam was king I heard that a railroad steam engine would move a ton of weight for 1 mile on 1 pound of coal and 1 cup of water. How does that compare to the diesels of today?

Nope, these trucks are typically rated at their top loaded speed. I've followed similar trucks down a haul road in a sand pit close to two miles long and can tell you without a doubt that they can run that fast loaded or unloaded either one. The ability to haul that much weight at that speed is what makes them profitable to operate as they can move more material per load, and more loads per day due to their speed, than a conventional dump truck could ever think about doing.

The rail industry claims they average 436 ton-miles per gallon of diesel. I don't think you can get much more efficient than that.
436 ton miles per gallon

Don't forget air presure has weight,and the fasster you go the more pressure you have meens the more HP you need to move that ton of air pressure.

In a vacuum with no gravity a vehicle at speed will stay at speed without any power. All else is different. I cannot believe the ideas that are left out of the equations!! How to explain that horse power is work, Lifting 33,000lbs one foot in one minute is about correct. Midsized autos use about 7 to8 hp at 50mph, assuming flat and level smooth concrete, no wind. It would not go up hills well, nor be able to accelerate up to speed well, but it is in that range that mid sized moderately aerodynamic cars operate. Faster equals dramatic increases in HP. It is a no win argument with some. Thanks for your clarity, Jim