Can someone please explain to me the difference between HP and torque. A friend told me that horsepower is what the engine produces while torque is what is actually delivered to the back wheels (in rear wheel drive). But in some posts here I've heard of "rear wheel HP" or something along those lines, refered to. So that kind of shoots down my friends explanation. It just seems to me that more HP should equal more torque. And yet I've seen some specs where a diesel engine will have so many HP but with gobs of torque while a gas engine will have gobs of HP but with lower torque...

My understanding of torque has always been "grunt" or pulling power. If that's the case wouldn't it be better to always have more horses and then just "simply" change the ratio of the rear end depending on towing requirements? Thanks for any help!

 

Here we go,

Torque is a force times a distance; hence lb-ft. So many pounds times 1 foot.
Horsepower is torque over time

1 hp = 550 lb-ft/second as in moving 550 lbs, 1 foot in 1 second against gravity.

*BUT* this doesn't exactly apply to engines producing power and torque.

A 600hp Caterpillar produces 2050 lb-ft of torque
A 600hp gas V-8 probably won't produce 800 lb-ft.

With different displacements, # of cylinders, different bores & strokes, turbos & superchargers, compression ratios, let alone what fuel they are burning all engines are different in the power they produce.

Their is also another huge difference between gas and diesel engines, from a thermodynamics perspective. The Diesel cycle is different than the Otto (gasoline) cycle.

Hope this helps...


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1999 Ford F150 XLT Supercab, Shortbed, 4x2, 4 wheel disc brakes/4 wheel Anti-Lock Brakes, Cloth Seats, Amazon green, 16" All season tires, Soft Tonneau Cover, CD Player, 4.6 liter Triton V8, 3:55 ls, towing package, 4 speed auto, K&N Airfilter
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Fast46Triton

The Terminator!

 

i agree with fast46triton with the formaul but i think it is a electrical one. i've always been told that you need torque to make horsepower. which i think is done with the camshaft. if you are towing you need more torque than horsepower and the rear gear needs to be in the top torque band and not in the top horsepower band. so if you are going to change the rear gear you need to find the max. rpm of torque band and stay in it. i hope i am right and this help. good luck

 

Torque is low rpm power (for towing)
Peak horsepower is high rpm power(for acceleration)
can't gear down horsepower to get required torque because that would be like driving in 2nd gear (too many rpm)

 

The formula relating the two is:

HP = T * N / 5252

Where T is in ft-lbs and N is in RPM.

Torque is the rotational equivalent of the force available to do work, in this case accelerate the vehicle.

Power expresses the time rate at which that work can be done. In automotive terms, this is most closely related to the speed which can be reached in a certain distance, such as a 1/4 mile or to the absolute top speed of a given vehicle.

What you feel while you are driving, or towing or hauling a load is torque.

 

I have always used a simple rule,

Torque gets you going and horsepower keeps you going.

I am not sure if it is accurate but it does make sense.

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'99 XLT S/C 4.6 Auto 3.55 LS Oxford White,Orlando appearance package, trailer tow package, keyless entry, A.R.E. Hard tonneau, ventvisors and bug guard all painted to match, limo tint, 5 spoke aluminum wheels, Kenwood 6 Disc, black Back Country nerfs, Buccaneers front license plate! I Luv it!

 

As I have always understood it, Torque is the power produced by an engine. HP is the relation of torque to the RPM range of the engine. Different engines will have different torque curves. Therefore as one stated earlier, one 500 ftlbs of torque motor may produce 300 HP and a different type of 500 ftlbs motor may have 350HP. Each engine bore/stroke/rod combo has its own HP and Torque curve +/- effeciency rating.

 

Torque is force. It is the rotational force the engine can produce. This force is connected to the wheels and pushes the vehicle. So, a higher torque engine can push a heavier load. It is a measure of doing work.

The best simple explanation I have heard for HP is that it is a measure of how fast the work can be done.

So if you wanted to lift a 100 lb weight 1 foot, you need to do 100 ft-lb of work. Let's say you have a 1 HP engine and a 50 HP engine (both are rated at 100 ft-lb). The 1 HP engine could lift the 100 lb weight as can the 50 HP engine. However the 1 HP engine would take more time to lift the weight than would the 50 HP engine.

So, relating this to motor vehicles, I would say that you must have enough torque to move the load. More torque allows you to pull a heavier load. "Extra" torque above what is needed makes it easier for the engine to do the job. Once you've got the torque to do the moving, a higher HP engine will let you accelerate the load faster.

Just trying to confuse things a little more...

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Danny
'98 F-150 Std., RC, SB, 4x2, 4.2L, 5-sp, 3.08, AC, speed control, rear slider
with Syntec engine oil, MTL trans fluid, Edelbrock shocks, 50 Series Flowmaster, K&N with airbox mod, electric radiator fan

 

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