The Great Torque vs. Horsepower Debate

[einzlr]

levels

[Gardus@Supersprint]

I'd like something like this for my car:


I don't care if the engine runs out of power after 6000 rpm...
Guess what car it is...

If you want low range torque AND upper range power:

[whataboutbob]

The OP did an excellent job on this writeup. It reminded me of my Physics teacher in my lower division Engineering classes.

[serialk11r]

Originally Posted by madfast

low tq/high rpm engines have to make use of gearing, but lets not forget that in real life there is a practical limit to gearing.

Sure, but I think most people who complain have a hard time understanding the concept of the downshift. Basically every car maxes out first gear by 45mph or so, as long as you're above 30mph you should have 80-90% of the power of the engine available. What's the point of "kick in the pants" feel at low speed anyways? You can accomplish that by buying a giant SUV that pitches backwards 10 degrees off the line, or dumping the clutch.
"I don't to want to sound like an ass by revving so high!" If you don't want to use half your rev range, maybe you should just get a diesel, you won't be able to tell the difference since you only use the same rev range anyways.
"I want to pass people by just putting my foot down!" Oh you can, it's called an automatic transmission.

Even people with torque monster V8s complain about passing power in top gear...you can never be satisfied if you expect the engine to do something it wasn't designed to do. Downshift and enjoy the power the way it was meant to be.

[einzlr]

Originally Posted by serialk11r

Sure, but I think most people who complain have a hard time understanding the concept of the downshift. Basically every car maxes out first gear by 45mph or so, as long as you're above 30mph you should have 80-90% of the power of the engine available. What's the point of "kick in the pants" feel at low speed anyways? You can accomplish that by buying a giant SUV that pitches backwards 10 degrees off the line, or dumping the clutch.
"I don't to want to sound like an ass by revving so high!" If you don't want to use half your rev range, maybe you should just get a diesel, you won't be able to tell the difference since you only use the same rev range anyways.
"I want to pass people by just putting my foot down!" Oh you can, it's called an automatic transmission.

Even people with torque monster V8s complain about passing power in top gear...you can never be satisfied if you expect the engine to do something it wasn't designed to do. Downshift and enjoy the power the way it was meant to be.

+1 on all points ...with the caveat that only really good "sporty" automatics do that for you. A lot of them are set up to keep the revs low, and when you floor it to pass (or avoid getting hit (!)), there's ... just ... no ... response

[gmookher]

Originally Posted by whataboutbob

The OP did an excellent job on this writeup. It reminded me of my Physics teacher in my lower division Engineering classes.

its a good cut and paste but there is no 'vs'
http://www.hotrod.com/techarticles/h...e/viewall.html

[ayau]

Hp sells cars, but is meaningless without seeing the hp/torque curve.

Your average joe just knows that the more hp, the faster the car.

[ayau]

I think the hp vs torque title is misleading. Hp is just a function of torque and rpm. Comparing hp and torque doesn't make sense. It also doesn't help when car salesmen stick to marketing hp to the general public, thus skewing the hp and torque terms even more.

[einzlr]

Originally Posted by ayau

I think the hp vs torque title is misleading. Hp is just a function of torque and rpm. Comparing hp and torque doesn't make sense. It also doesn't help when car salesmen stick to marketing hp to the general public, thus skewing the hp and torque terms even more.

Doesn't help? It helps them sell cars; that's all that matters, right?

[White Shadow]

Originally Posted by serialk11r

Even people with torque monster V8s complain about passing power in top gear...you can never be satisfied if you expect the engine to do something it wasn't designed to do. Downshift and enjoy the power the way it was meant to be.

That's because a lot of V8 cars have very tall gearing for their top gear. That's mostly to help with highway fuel economy. I had a V8 Mustang that made a ton of torque, but if I floored that car in top gear at 60 MPH, it went absolutely nowhere. It almost felt like the fuel line was crimped off. I had to downshift to get any passing power at all.

I also owned a M3 (6-cylinder, not the new 8-cylinder car) that had TONS of passing power in top gear on the highway. There was never any reason to downshift to pass someone on the highway. The car would pull very hard in top gear at 60 MPH.

And right now I have a 4-cylinder turbo engine in my car that also pulls very hard in top gear at highway speeds. No need to downshift to pass anyone on the highway. The engine makes fantastic low-end torque, so it can still have decent overdrive gearing (in top gear) and it still manages to pull hard on the highway. That's the best of both worlds.

[serialk11r]

Originally Posted by White Shadow

That's because a lot of V8 cars have very tall gearing for their top gear. That's mostly to help with highway fuel economy. I had a V8 Mustang that made a ton of torque, but if I floored that car in top gear at 60 MPH, it went absolutely nowhere. It almost felt like the fuel line was crimped off. I had to downshift to get any passing power at all.

I also owned a M3 (6-cylinder, not the new 8-cylinder car) that had TONS of passing power in top gear on the highway. There was never any reason to downshift to pass someone on the highway. The car would pull very hard in top gear at 60 MPH.

And right now I have a 4-cylinder turbo engine in my car that also pulls very hard in top gear at highway speeds. No need to downshift to pass anyone on the highway. The engine makes fantastic low-end torque, so it can still have decent overdrive gearing (in top gear) and it still manages to pull hard on the highway. That's the best of both worlds.

To get that large amount of reserve power in top gear, the tradeoff is worse fuel economy. The only way to get around that is forced induction (or hybrid), and you still lose fuel economy for that unless you have a rather sophisticated system like variable vane turbo, clutched pulley SC, or future variable speed SC/electrically driven SC.

IMO, if the last gear is anything more than just enough to keep the car going up a hill on the highway, it's too short. The downshift is where the fun is at!

[White Shadow]

Originally Posted by serialk11r

To get that large amount of reserve power in top gear, the tradeoff is worse fuel economy. The only way to get around that is forced induction (or hybrid), and you still lose fuel economy for that unless you have a rather sophisticated system like variable vane turbo, clutched pulley SC, or future variable speed SC/electrically driven SC.

IMO, if the last gear is anything more than just enough to keep the car going up a hill on the highway, it's too short. The downshift is where the fun is at!

That's why so many powerful V8 cars have such tall overdrive gears....it's to allow them to get some kind of decent fuel economy on the highway.

The beauty of a turbo is that they help a small engine make very good low-end torque. And that's the kind of torque needed to allow a car to have the kind of flexibility it takes to return decent highway fuel economy while still having decent passing power without having to downshift.

My car, for example, will return more than 30 MPG on the highway while still having plenty of passing power in top gear. At 60 MPH in top gear, the engine is only turning around 2500 RPM, so that's probably a big reason why it will still get more than 30 MPG on the highway. The great low-end torque is probably a bigger factor than the gearing in my particular car when it comes to top gear passing power.

BTW, Car and Driver magazine publishes top gear acceleration numbers (both 30 - 50 MPH and 50 - 70 MPH) for all of their road tests. The reason they provide those numbers is to give us a sense of how flexible the engine is when it comes to its power & torque bands. Those numbers are obviously much more useful for manual transmission vehicles though....