Help explaining horsepower and torque feel

[Coyotes55086]

Thanks alot for that response man ! so a truck like a 3500 6.7l turbo diesel, its has like 930ft lb trq and like 430 hp . would all that torque make it feel fast on the bottom end or in low rpms? or would it require more power to make it feel faster ?

Sponsored

 

[SplawnDarts]

Thanks alot for that response man ! so a truck like a 3500 6.7l turbo diesel, its has like 930ft lb trq and like 430 hp . would all that torque make it feel fast on the bottom end or in low rpms? or would it require more power to make it feel faster ?

OK, I'm not personally familiar with that engine but let's find a dyno curve for it:

https://www.ford-trucks.com/wp-cont...6-7-power-stroke-including-2015-updates19.jpg

Note that this curve looks weird because the torque and HP aren't on the same scale, so the crossover isn't at 5252 where it would normally be.

Of course this engine can't turn at 5252 RPM... The first thing to note is that redline is like 3400 and max power is at 2800.

Now, how does it compare to say a stock coyote pulled from a mustang? Well, if you used the gearing from the F350, the coyote would have a real problem. The truck engine is designed to run at low RPM - it's happy at say 1800 RPM and makes about 250 hp there. The coyote makes less than 100 hp there and would be badly lugged under load.

Here's the thing though, if you were going to put a coyote in that truck, it would NOT be geared the same. As a starting point let's say it was geared down so that it's HP peak of 7500 was at the same point as the 6.7L's HP peak at 2800 - so the coyote would be geared down by an additional ratio of 2.68:1 either in the transmission or the transfer case or rear end. In the real world you wouldn't do exactly that, but it will serve for this example. Now, instead of operating at 1800 RPM the coyote would be operating at 4820 RPM where the it makes about 350hp. So that little 'ol coyote would actually move that big F350 out faster than the 6.7L if it was geared to match the max HP points. Of course with that gearing you'd now have to drive your truck like it was a racecar and live in the high RPM range.

We don't put high strung little coyotes in F350s for wear and other reasons, but this serves to illustrate why torque is a lousy way to think about the world: it doesn't survive gearing changes. By gearing down the coyote to match it to the application better we gave it higher rear wheel torque (proportional to it's higher HP) than the 6.7L. The coyote only makes about 400 crank tq, but it will out accelerate the 6.7L even near the torque peak of the 6.7L if geared to do so because it makes more power.

In general, power to weight ratio is a pretty good proxy for acceleration assuming both vehicles have drivetrains that let them operate near their HP peaks. There's more to the story, but that's the basics.

 

[ponie1992]

This video gives a great explanation and also gives an idea of what you "feel".

 

[ponie1992]

You ”feel” the impact of torque at the wheels. You don’t “feel” horsepower in any way shape or form.
Peak acceleration for a given gear occurs at peak torque. Period.
Dyno chart from a Camaro below to graphically illustrate for the OP how the peak accel happens early (in this case) but the driver will hold the gear regardless, cos he wants to capitalise on the torque multiplication of that gear, rather than shift up.

Incorrect.
Power translates to acceleration. You can feel acceleration.

 

[Burkey]

Incorrect.
Power translates to acceleration. You can feel acceleration.

Acceleration is calculated by dividing the Force (Torque) by mass, if you want to argue against that, you need to take it up with the laws of physics.

Why does a car accelerate faster in first gear than fourth whilst the horsepower at the tyres hasn’t changed? That’s right, the exertion of more torque at the wheels.

You make more horsepower by creating more torque (for a given rpm).

 

[SplawnDarts]

Acceleration is calculated by dividing the Force (Torque) by mass, if you want to argue against that, you need to take it up with the laws of physics.

Why does a car accelerate faster in first gear than fourth whilst the horsepower at the tyres hasn’t changed? That’s right, the exertion of more torque at the wheels.

You make more horsepower by creating more torque (for a given rpm).

The problem with using torque as a means of measuring engine performance is that it is dependent on the overall drive ratio. It's only torque/force at the tires that matters. Torque at the crank, which is always what gets reported, tells you essentially nothing. That's why in the example above, the 800+ lb-ft diesel can't accelerate the truck as fast as the 400 lb-ft coyote even though the diesel is operating very close to its torque peak. The coyote gets geared down, and ends up making more torque/force at the wheels than the diesel. Torque at the crank doesn't mean squat.

On the other hand HP at the crank is VERY meaningful, because other than drivetrain losses it's the same as HP at the wheels and doesn't care about gearing/drive ratios at all.

 

[Jackson1320]

So when supercharging a car (s550) stock being 435hp and 400lb trq , the car say can go to 650hp and 500lb trq
. What do you notice in the ride ? is it the horsepower or the torque ?

what would be the difference in a ride that is say 500hp 700lb trq vs the opposite ratio 700hp vs 500ft torque? is there a difference in feel here ? or do they feel the same?

Horsepower is just a mathematical equation based on torque and RPM. more torque or more RPM equals more horsepower

 

[Avispa]

What makes the car fun to drive is area under the torque/RPM curve. All else being equal between comparisons, a bigger area under the curve makes the car feel like it gets from point at to point b faster. The torque curve area is a measure of the amount of energy the motor can put to the wheels.

 

[Jackson1320]

The problem with using torque as a means of measuring engine performance is that it is dependent on the overall drive ratio. It's only torque/force at the tires that matters. Torque at the crank, which is always what gets reported, tells you essentially nothing. That's why in the example above, the 800+ lb-ft diesel can't accelerate the truck as fast as the 400 lb-ft coyote even though the diesel is operating very close to its torque peak. The coyote gets geared down, and ends up making more torque/force at the wheels than the diesel. Torque at the crank doesn't mean squat.

On the other hand HP at the crank is VERY meaningful, because other than drivetrain losses it's the same as HP at the wheels and doesn't care about gearing/drive ratios at all.

When you Dyno a car it does not give you the torque at the crankshaft. it’s gonna give you the torque at the wheels. after all you’re gearing and anything else without torque you cannot have horsepower. Your horsepower is directly calculated from your torque. [ torque Multiplied by RPM divided by 5252 equals horsepower] Every dyno in the world uses torque to measure an engine. Then it does the math and spits out your horsepower

 

[SplawnDarts]

When you Dyno a car it does not give you the torque at the crankshaft

Wrong. They back out the drive ratio in an attempt to give engine torque. There are drivetrain losses of course, but other than that it's engine torque not wheel torque. Which is why what you get isn't dependent on what gear you use for the dyno pull.

 

[Jackson1320]

Wrong. They back out the drive ratio in an attempt to give engine torque. There are drivetrain losses of course, but other than that it's engine torque not wheel torque. Which is why what you get isn't dependent on what gear you use for the dyno pull.

Horsepower and torque are both depending on the gear

 

[Jackson1320]

Wrong. They back out the drive ratio in an attempt to give engine torque. There are drivetrain losses of course, but other than that it's engine torque not wheel torque. Which is why what you get isn't dependent on what gear you use for the dyno pull.

Horsepower is an equation based on torque not an opinion it’s a fact I’ve already given you the equation

 

[SplawnDarts]

Horsepower is just a mathematical equation based on torque and RPM. more torque or more RPM equals more horsepower

Yes. The key point though is that HP is gearing-independent. When you gear down by say a 2x ratio, you double the torque and halve the RPM. If all you look at is torque, you'd think you'd doubled your output but of course that's not true.

 

[SplawnDarts]

Horsepower is an equation based on torque not an opinion it’s a fact I’ve already given you the equation

And yet you continue to not understand.

Just because you can copy an equation I already posted doesn't mean you understand it

 

[Jackson1320]

And yet you continue to not understand.

Just because you can copy an equation I already posted doesn't mean you understand it

I understand that every dyno in the world uses torque to measure an engine. When you Dyno an engine there should be no gear ratio to it. it’s supposed to be done as close to 1 to 1 as possible. if you dyno a car in a lower gear ratio you’re going to change the torque and horsepower information. Because you’re multiplying it’s torque and horsepower.

To get back to OP question torque you are going to feel more off the line and horsepower you feel as the RPMs build. That’s why cars with low torque but high horsepower they use trans break and a stall converter so they can takeoff when they already have RPM

Sponsored