IMO all of the above is out of context. I prefer to apply the science of engine torque to the selection of motorhomes and chassis (whenever one is purchasing a motorhome), and I assume that the buyer already knows the required task/mission.
I also do NOT apply the textbook definition of torque to the selection of engines simply because I know that RPM is present throughout the published torque curves of all engines (for motorhomes). Let's face it, this is quite different than a rock on the end of an arm (static torque). Also, I do not engage in talks which apply only if you are designing an engine from scratch. I only look at the engines which are available for the type of motorhome which suits the mission. Once I select the "box", then I look at the available options on chassis and engine combinations. Then, I simply go with the engine which produces the most torque. I happen to know that the horsepower thing will take care of itself.
Willie & Betty Sue
Miko & Sparky
2003 41 ft Dutch Star Diesel Pusher/Spartan
Floorplan 4010
Blazer toad & Ranger bassboat
I believe a much better test would be as follows.
Take a 20,000 lb vehicle and run the diesel and then switch the motor and run the gas motor. Record the difference.
Now switch to a 50,000 lb vehicle and run the exact same test.
The difference between the Diesel and gas motors will be very apparent.
The test as described above is taking the smaller of the diesel engines and pits it against the largest of the gas motors. Could we go back and run the test against say a 350 hp Cummins or cat where the torque is at least a couple of hundred pound feet more.
Next test is to run the gas motor VS the Diesel for a sustained amount of time lets keep that load on both of them for several hundred hours. Which do you think will get the most wear.
Last look at the heavy trucking industry they rely on torque to carry the loads. Gas motors are very rarely used.
I am not saying that anyone in this forum should choose gas or diesel. I am saying that when comparing torque to horsepower against Gas Vs Diesel as in this post, the 0-60 and how fast we go up the hill is a very small part of the horsepower vs torque comparison.
93 Airstream 35' Dp
5.9 230 uprated to 300 HP
Allison MD 3060
Dutchess and Shadow (fur Bearing Children)
The higher the torque & horsepower, the higher the cubic inches. Adding Banks systems & other power devices to smaller engines usually the wear & maintanence, so the only replacement for cubic inches is cubic cash.
dennis16002 wrote: The higher the torque & horsepower, the higher the cubic inches. Adding Banks systems & other power devices to smaller engines usually the wear & maintanence, so the only replacement for cubic inches is cubic cash.
I cannot agree with that because the best thing I gained from a Banks System is better exhaust manifold heat dissipation and "three" cooler heads.
Engines do not produce the rated HP under most real world conditions. Gas engines (non turbo) lose about 3% / 1,000 feet above sea level, and they lose as temperature rises and so on. A 340 HP gas engine is not likely really putting out 340 HP. Diesel engines which are turbo charged have an advantage. They generally lose little due to elevation, and the aftercooler helps keep the temperature variationn lower. Drive train losses between a diesel and gas chassis are also different. Also, torque is a measure of force, and HP is, by definition, a measure of work.
Whether you look at the physics book or the CAT web site, theory says that HP will determine acceleration and hill climbing capability. I was really confused as to why so many drivers swear by their high torque engines. After some investigation, I think I found the answer. I looked at the engine power curves for my Ford V-10 and a similar HP diesel engine. It was apparent that the difference is that the diesel cruises with the engine speed much closer to the HP peak. (Don't know why it still gets good mileage with much lower gearing than a gas engine). Anyway, the result is that the gas engine has much less HP available without shifting down. So when you press the gas to the floor to climb a hill, the diesel will have more power available, and will climb better. When the engine shifts down, the diesel will need to go down only one gear to hit the HP peak, while the gasser will likely need to go down two, and will be operating at a much higher and noisier RPM than the diesel. I believe the theory is correct that for for equal HP and weight, both will perform the same. But the perception of the driver will certainly be that the higher torque provides better hill climbing performance, because the engine does not appear to be working as hard.
Ed
ed1 wrote: Whether you look at the physics book or the CAT web site, theory says that HP will determine acceleration and hill climbing capability. I was really confused as to why so many drivers swear by their high torque engines. After some investigation, I think I found the answer. I looked at the engine power curves for my Ford V-10 and a similar HP diesel engine. It was apparent that the difference is that the diesel cruises with the engine speed much closer to the HP peak. (Don't know why it still gets good mileage with much lower gearing than a gas engine). Anyway, the result is that the gas engine has much less HP available without shifting down. So when you press the gas to the floor to climb a hill, the diesel will have more power available, and will climb better. When the engine shifts down, the diesel will need to go down only one gear to hit the HP peak, while the gasser will likely need to go down two, and will be operating at a much higher and noisier RPM than the diesel. I believe the theory is correct that for for equal HP and weight, both will perform the same. But the perception of the driver will certainly be that the higher torque provides better hill climbing performance, because the engine does not appear to be working as hard.
Ed
Good analysis----plus whatever engine noise the diesel does make is way behind the driver.
And (from the muscle car days) too much HP is just right!!!!
Mark
2000 Itasca Suncruiser 35U on a Ford chassis
2003 Ford Explorer toad with US Gear brakes,
ReadyBrute tow bar, and Demco base plate.
ed1 wrote: Whether you look at the physics book or the CAT web site, theory says that HP will determine acceleration and hill climbing capability. I was really confused as to why so many drivers swear by their high torque engines. After some investigation, I think I found the answer. I looked at the engine power curves for my Ford V-10 and a similar HP diesel engine. It was apparent that the difference is that the diesel cruises with the engine speed much closer to the HP peak. (Don't know why it still gets good mileage with much lower gearing than a gas engine). Anyway, the result is that the gas engine has much less HP available without shifting down. So when you press the gas to the floor to climb a hill, the diesel will have more power available, and will climb better. When the engine shifts down, the diesel will need to go down only one gear to hit the HP peak, while the gasser will likely need to go down two, and will be operating at a much higher and noisier RPM than the diesel. I believe the theory is correct that for for equal HP and weight, both will perform the same. But the perception of the driver will certainly be that the higher torque provides better hill climbing performance, because the engine does not appear to be working as hard.
Ed
Well stated – wish I had explained it that way!
One other aspect of this discussion is that there have been a lot of misleading statements about units and power. Here is a brief summary of definitions:
Linear –
Force is a static measurement
Work or energy is force X distance
Power is work in a unit of time or force X speed
Rotary -
Torque is a static measurement
Work or energy is torque X number of turns
Power is work in a unit of time or torque X RPM
The point I really trying to make was the test results on page 63 of the February issue of Motorhome magazine. They tested two Identical as possible, except for torque, Winnebago Ind. model 39W MH's on the UFO chassis. The test showed the Gas engine ( 340 Hp and 455 ft-lbs torque ) had faster acceleration and hill climbing than the diesel ( 340 hp and 660ft-lbs of torque ). Maybe because it weighted 1200 pound less. In this test at least the addition 205 ft-lbs of torque did not lead to increased acceleration or hill climbing speed.
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