MChalkley
Elite Member
- Joined
- Mar 27, 2000
- Messages
- 3,198
- Location
- Eastern Virginia
- Tractor
- EarthForce EF-5 mini-TLB (2001)
This has sure been an interesting thread. Here's something that's been referred to, but not hit directly, unless I missed it (not unlikely...):
To simplify it as far as it can possibly be distilled to (by me - and all the old-timers here will tell you I'm not known for simplifying things!), torque is defined as a twisting force, while horsepower is defined as a specific amount of work over a specified amount of time. The key element here is the expression "over time". You can really only compare engines of different horsepower ratings if you're trying to compare the speed at which the work will get done. If you're trying to find out how much work they'll do, you better use torque, because it's the only one that measures what you want to know.
To repeat a story I've told here a few times: I was getting out of my '93 Dodge (Cummins, W250) in a WalMart parking lot a few years ago, just as a young (too young) guy was getting out of his jacked-up 350-powered Chevy with the obligatory performance-related stickers was getting out of his. I'm minding my own business and he says something like "Diesels!!! Good fuel economy, but if you want power you need a gas engine. I'll bet my 350 will blow the doors off your Cummins from a stop light any day." So I said, I'll take you up on that bet, if you'll back your gas engine up to my diesel, let me chain the hitches together. Then, if your hitch holds, after I drag your butt around the parking lot a few minutes, and rip the drivetrain out from under yours, I'll mosey on down to that stop light and be the only one in the race." He wasn't willing to accept the race on my terms, for some reason. But the conversation illustrates the point of this discussion. I have no doubt that his gas engine, with more hp, would take my diesel from a light. I also have no doubt whatsoever that my diesel with way more torque would drag his truck around backwards until it ran out of fuel (which would be long after his gas engine ran out, FWIW).
Another illustration of the same point: In '96 Edmunds (the car review and price guide people), did a "review" of the VW Passat. Their verdict (from an engine standpoint): the V6 was a very respectable performer, the 115hp gas engine barely adequate, but the 90hp diesel "woefully underpowered" (yes, those are quotation marks). Now, Car and Driver, more noted for Testarossa testing than VW diesel testing, also reviewed the 90hp TDI and said it easily ran away from the 115hp gas engine model and kept up with the V6 surprisingly well. In fact, if memory serves me correctly, they said it was only after the cars reached 70 or so mph that the V6 began to convincingly pull away. So, how did Edmunds blow it so badly? Simple: They didn't drive the diesel, and they forgot their basic physics. (I'm being charitable here by using the word "forgot" - privately I don't think the person who wrote the "review" ever knew the difference.) At any rate, confusion over the terms and what they mean is obviously very common, as this reviewer's huge mistake shows.
One last point: torque is always measured, while hp is always calculated (and no, I'm not forgetting that there are devices that "measure" hp and show it on a gauge - they're still calculating it). What's it calculated from? Why, torque, of course. And why is it calculated? Because time is the other half of the equation.
To simplify it as far as it can possibly be distilled to (by me - and all the old-timers here will tell you I'm not known for simplifying things!), torque is defined as a twisting force, while horsepower is defined as a specific amount of work over a specified amount of time. The key element here is the expression "over time". You can really only compare engines of different horsepower ratings if you're trying to compare the speed at which the work will get done. If you're trying to find out how much work they'll do, you better use torque, because it's the only one that measures what you want to know.
To repeat a story I've told here a few times: I was getting out of my '93 Dodge (Cummins, W250) in a WalMart parking lot a few years ago, just as a young (too young) guy was getting out of his jacked-up 350-powered Chevy with the obligatory performance-related stickers was getting out of his. I'm minding my own business and he says something like "Diesels!!! Good fuel economy, but if you want power you need a gas engine. I'll bet my 350 will blow the doors off your Cummins from a stop light any day." So I said, I'll take you up on that bet, if you'll back your gas engine up to my diesel, let me chain the hitches together. Then, if your hitch holds, after I drag your butt around the parking lot a few minutes, and rip the drivetrain out from under yours, I'll mosey on down to that stop light and be the only one in the race." He wasn't willing to accept the race on my terms, for some reason. But the conversation illustrates the point of this discussion. I have no doubt that his gas engine, with more hp, would take my diesel from a light. I also have no doubt whatsoever that my diesel with way more torque would drag his truck around backwards until it ran out of fuel (which would be long after his gas engine ran out, FWIW).
Another illustration of the same point: In '96 Edmunds (the car review and price guide people), did a "review" of the VW Passat. Their verdict (from an engine standpoint): the V6 was a very respectable performer, the 115hp gas engine barely adequate, but the 90hp diesel "woefully underpowered" (yes, those are quotation marks). Now, Car and Driver, more noted for Testarossa testing than VW diesel testing, also reviewed the 90hp TDI and said it easily ran away from the 115hp gas engine model and kept up with the V6 surprisingly well. In fact, if memory serves me correctly, they said it was only after the cars reached 70 or so mph that the V6 began to convincingly pull away. So, how did Edmunds blow it so badly? Simple: They didn't drive the diesel, and they forgot their basic physics. (I'm being charitable here by using the word "forgot" - privately I don't think the person who wrote the "review" ever knew the difference.) At any rate, confusion over the terms and what they mean is obviously very common, as this reviewer's huge mistake shows.
One last point: torque is always measured, while hp is always calculated (and no, I'm not forgetting that there are devices that "measure" hp and show it on a gauge - they're still calculating it). What's it calculated from? Why, torque, of course. And why is it calculated? Because time is the other half of the equation.