Applying Torque vs Horsepower

[EricSMG]

So how does this compare to the viper acr which has more torque than hp? I think it has like 600ftlbs. And it's winning every race on every track just about.

Tons of torque and tons of power for the weight. Plus all of the other track-specific tuning it has. It can put down all that torque and has tons of aero and grip.

Of course torque matters - it's what horsepower is derived from - but "low" rpm torque doesn't make a car "fast" if you don't also have the horsepower, which requires rpm.

A good analogy it to imagine driving a large nail with a hammer.

Low rpm: hit the nail once every 5 seconds.
High rpm: hit the nail once very 1 second.

If you hit the nail with the same force (torque) you will drive the nail into the wood MUCH sooner at 1 hit per second. This is more horsepower. Torque did not change. High rpm torque was much faster than low rpm torque even though torque was the same.

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[Coolmanfoo]

Tons of torque and tons of power for the weight. Plus all of the other track-specific tuning it has. It can put down all that torque and has tons of aero and grip.

Of course torque matters - it's what horsepower is derived from - but "low" rpm torque doesn't make a car "fast" if you don't also have the horsepower, which requires rpm.

A good analogy it to imagine driving a large nail with a hammer.

Low rpm: hit the nail once every 5 seconds.
High rpm: hit the nail once very 1 second.

If you hit the nail with the same force (torque) you will drive the nail into the wood MUCH sooner at 1 hit per second. This is more horsepower. Torque did not change. High rpm torque was much faster than low rpm torque even though torque was the same.

Great post. I think that was the best, easiest to understand analogy yet!

 

[GT Pony]

The statement, as I've heard it, is "horsepower sells cars but torque wins races."

HP wins races. Look at an F1 car ... low torque, but high HP due to RPM (recall that HP = T X RPM/5252). Match the HP curve to the proper gearing and you win races.

 

[PJR202]

Tons of torque and tons of power for the weight. Plus all of the other track-specific tuning it has. It can put down all that torque and has tons of aero and grip.

Of course torque matters - it's what horsepower is derived from - but "low" rpm torque doesn't make a car "fast" if you don't also have the horsepower, which requires rpm.

A good analogy it to imagine driving a large nail with a hammer.

Low rpm: hit the nail once every 5 seconds.
High rpm: hit the nail once very 1 second.

If you hit the nail with the same force (torque) you will drive the nail into the wood MUCH sooner at 1 hit per second. This is more horsepower. Torque did not change. High rpm torque was much faster than low rpm torque even though torque was the same.

Finally. Thank you. People keep saying the horsepower kicks in or the race is won because the horsepower was higher even though torque was lower but I still don't think everyone is grasping that horsepower IS torque x RPM ÷ 5252. Horsepower is TORQUE AT RPM.

All things being semi equal, the car that wins the race is the one making peak torque at the most critical RPM for the car to go faster in the right point in the race to take or maintain the lead. Call that horsepower of you like but there is no horsepower without torque just like there's no french toast without eggs.

 

[Norm Peterson]

Finally. Thank you. People keep saying the horsepower kicks in or the race is won because the horsepower was higher even though torque was lower but I still don't think everyone is grasping that horsepower IS torque x RPM ÷ 5252. Horsepower is TORQUE AT RPM.

This ↑↑↑.

In nearly all cases (crudely), the product of [torque @ rpm] times [transmission gearing x axle gearing] ends up being greater in the lowest usable gear at the higher rpm. Even when the rpm required for the car speed ends up being slightly past the rpm of peak HP. You're still gaining more from the lower gearing than you're losing from torque drop-off past the torque peak.

I think what keeps people confused is that maximum possible acceleration with any given gearing isn't the same thing as maximum possible acceleration at any given speed. The first happens at peak torque (and its rpm), the second requires gearing to put peak HP rpm at that speed, and they aren't going to be the same.


Norm

 

[MattW]

Here is my view. For the car

acceleration = power / speed / mass

As your speed increases you need more power to accelerate the same amount. The power comes from the engine, for which

power = torque * rev-rate

In order to provide the power to accelerate the car, the engine either must provide lots of torque up to some rev-rate or maintain torque at high rev-rate. For example, race engines are designed to maintain decent torque at high rev-rates (e.g., F1 at 15,000 rpm) to deal with high speed. I'm guessing trucks are designed to provide high torque up to some moderate rev-rate to deal with accelerating large mass.

 

[TexasRebel]

A good analogy it to imagine driving a large nail with a hammer.

Low rpm: hit the nail once every 5 seconds.
High rpm: hit the nail once very 1 second.

If you hit the nail with the same force (torque) you will drive the nail into the wood MUCH sooner at 1 hit per second. This is more horsepower. Torque did not change. High rpm torque was much faster than low rpm torque even though torque was the same.

Your analogy fails in that you're using the same size hammer. Low end torque would be hitting the nail once every 5 seconds with a 20# hammer while high end horsepower would be hitting the nail every second with a 3# hammer.

One of the advantages of low-torque high RPM engines is the weight savings. With high torque comes bigger parts (rods, pins, crankshaft, gears, &c.).

 

[MattW]

One of the advantages of low-torque high RPM engines is the weight savings. With high torque comes bigger parts (rods, pins, crankshaft, gears, &c.).

Right. One must take into account that part of the engine power goes into generating mechanical energy (e.g., spinning the flywheel, crankshaft, etc) that does not go to the wheels.

 

[PJR202]

HP wins races. Look at an F1 car ... low torque, but high HP due to RPM (recall that HP = T X RPM/5252). Match the HP curve to the proper gearing and you win races.

I missed this earlier. I don't disagree with your formula, obviously, but the horsepower didn't win the race. That's the part people need to get our of their head when evaluating a vehicle. The horsepower isn't what is making the car move. The torque alone doesn't win the race, but regardless of the RPM horsepower doesn't exist without torque. The engine creates torque and it achieves RPM, both by design. It doesn't create or achieve horsepower. It's the reason a new SS beats a new GT--the engine makes 50 lb/ft higher in torque at similar rpm. That's a big advantage.

This is why the statement (based on the two primary power numbers used to brag on or sell a vehicle) that torque wins races is more accurate.

 

[crs2879]

Constantly seeing the Mustang v Camaro comparison is only relevant because they are similar cars (2 door, sport coupes). The Coyote is a 5.0 Liter, DOHC, 4V while the SS is a 6.2 Liter pushrod, 2V engine. What GM has done with the LS architecture is pretty amazing but it is difficult to overcome cubic inches without some form of forced induction. The fanboy arguments are entertaining but the 2 engines are similar in cylinder count....and not much else. 1.2 liters of displacement is where the greater torque numbers of the Chevy come from.

 

[Coolmanfoo]

Well time for me to ask a question and hopefully not be massacred! With all this talk of rpms it got me thinking what is actually rotating? Is it the crankshaft? The flywheel? Ive never actually thought about what rpm was actually measuring I just knew how it related to driving and power.

 

[MattW]

Well time for me to ask a question and hopefully not be massacred! With all this talk of rpms it got me thinking what is actually rotating? Is it the crankshaft? The flywheel? Ive never actually thought about what rpm was actually measuring I just knew how it related to driving and power.

You can consider any of them. But you have to consider the torque and rev-rate at the same place. If you consider the input and output of the transmission, the power is the same (minus mechanical and friction losses) and so the torque scales inversely with the rev-rate. If the input rev-rate is 5000 rpm and input torque is 40 ft-lb, and the output rev-rate is 500 rpm then the torque at the output is 400 ft-lb.

 

[Dominant1]

Constantly seeing the Mustang v Camaro comparison is only relevant because they are similar cars (2 door, sport coupes). The Coyote is a 5.0 Liter, DOHC, 4V while the SS is a 6.2 Liter pushrod, 2V engine. What GM has done with the LS architecture is pretty amazing but it is difficult to overcome cubic inches without some form of forced induction. The fanboy arguments are entertaining but the 2 engines are similar in cylinder count....and not much else. 1.2 liters of displacement is where the greater torque numbers of the Chevy come from.

if you had a 376 cubic inch coyote motor vs a 302 cubic inch 2 valve motor both have 11:1 compression, how would that race turn out?

 

[pietran30]

if you had a 376 cubic inch coyote motor vs a 302 cubic inch 2 valve motor both have 11:1 compression, how would that race turn out?

A win for the Chevy cuz you wouldn't be fitting that coyote in anything.

 

[Seceda91]

A win for the Chevy cuz you wouldn't be fitting that coyote in anything.

LOL!

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