Are large gas motor Rv's underpower?
At the risk of getting someone angry for me asking the same question they don't want to see again, that no doubt some people feel has been discussed enough. Are gas Class A's underpowered to tow a...
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Mr. Mark, I am surprised you have not seen anyone talk about torque vs HP. We talk about it all the time. The problem with a torque spec is that it is incomplete, as it does not account for the torque multiplication of the drivetrain. If the engine is limited to low RPM, the drivetrain can not multiply the torque to the wheels because the gear ratio is too low. Basically, the diesel has little headroom to downshift. At freeway speeds, you can probably only go down one gear and gain a small amount of pull. I can drop 2 gears and smoke by most anything, including a lot of cars.
Torque gives the perception of power because all of the power the engine has is available without downshifting. When you do downshift, you don't gain much. For a high HP/lower torque gas engine, all of its available power is achieved by RPM, so when the engine spins faster, the gearing multiplies the torque to the drive wheels. Its simple math, but to prove it out, one needs to go through all the gear ratios and calculate wheel torque.
In the practical sense, very simply, the HP spec tells you how hard it will pull when the throttle is wide open. The torque spec gives you some indication as to how often you will downshift. People generally like a lot of torque, because they don't like the idea of downshifting. Ultimately while that is important, it doesn't tell you anything about how much it can pull up a hill.
BTY:There was an earlier comparison of a Duramax 300 hp/600ft-lbs torque. It was compared to a 454, which had 230 HP and 390ft-lbs of torque. 300HP vs 230HP which one is faster? well dah. Compare that to an 8.1 and the 8.1 will slowly pull away. (340HP /450ft-lbs torque) Still lower torque, but more powerful.
Torque gives the perception of power because all of the power the engine has is available without downshifting. When you do downshift, you don't gain much. For a high HP/lower torque gas engine, all of its available power is achieved by RPM, so when the engine spins faster, the gearing multiplies the torque to the drive wheels. Its simple math, but to prove it out, one needs to go through all the gear ratios and calculate wheel torque.
In the practical sense, very simply, the HP spec tells you how hard it will pull when the throttle is wide open. The torque spec gives you some indication as to how often you will downshift. People generally like a lot of torque, because they don't like the idea of downshifting. Ultimately while that is important, it doesn't tell you anything about how much it can pull up a hill.
BTY:There was an earlier comparison of a Duramax 300 hp/600ft-lbs torque. It was compared to a 454, which had 230 HP and 390ft-lbs of torque. 300HP vs 230HP which one is faster? well dah. Compare that to an 8.1 and the 8.1 will slowly pull away. (340HP /450ft-lbs torque) Still lower torque, but more powerful.
