Hey Guys,

A friend of mine asked me what the difference was between torque and horsepower were, I tried to explain it to him, but I only understand it minimally. Thanks for the help.

 

You sell horsepower, you drive torque

 

Torque gets you there H.P. keeps you there. Does this make any sense? Not sure it makes since to me either :D

 

Torque is a twisting force, measured in ft-lb or more correctly lb-ft units.

With regard to auto engines, the dyno measures/records torque vs RPM. Then HP is calculated from torque at each point by:
HP=Torque x RPM / 5252.

So torque is measured and HP is calculated.

As you can see, HP is related to the rate of exerting the twisting force, torque. For a flat torque curve, HP increases linearly with RPM till the torque starts to fall off.

To confuse things a little is common usage. What we usually mean by "torque" is that low RPM grunt that our L98s put out compared with say a LT1. So, even though the LT1 may generate lower torque, the torque curve continues flat to higher RPM than with the L98. Since HP is the product of torque x RPM, the LT1 builds more HP than the L98 simply because it's torque curve remains flat to higher RPM.

If you could see the torque and HP curves vs RPM of the L98 and the LT1 superimposed it would be very clear what is going on there. If interested, Charles Probst's book "Corvette Fuel Injection" has a plot of torque and HP vs RPM for the L98, LT1 and LS1 on the same graph. It's very enlightning and realy shows the differences between these engines.

Hope this sheds some light on the subject.

 

Good response, thanx for the info.
Allen

 

Not really an accurate conclusion - HP can just as easily be measured and torque calculated. For example this is what a dynojet does. I see this commonly as a result of the way the equation is normally written, but you can just as easily solve for torque.

If you click on our website and click on Tech we have a couple of writeups there, one a torque vs. hp discussion. For convienence I have pasted it here.
Torque

Torque is F dot d - the cross product of the force * the moment arm. Now force is obviously what pushes your car forward, and is the force you feel when you accelerate.

The real question is - which torque? It's not flywheel torque that actually moves your car, but rather "delivered torque", or torque * gear multiplication. This is why you accelerate faster in first gear than in third (ignoring wind resistance).
How does this work? Say at we have 300 ft-lbs of torque available at an rpm. Now in first let’s say a 4:1 tranny gear and 1:1 rear gear (to make math easier) - so a final drive ratio of 4:1. So in first gear we will have 300 * 4 = 1200 ft-lbs of torque pushing us forward. Say second gear is 2:1 - so we have 300 * 2 = 600 ft-lbs of torque pushing us forward. 1200 is obviously more than 600, and accounts for that difference.

Now let's look at this a little differently. Gearing is fixed for each gear, so velocity and rpm are related.

Say we have 300ft-lbs of torque @ 3500, and 300hp at 7000 rpm (only 225 ft-lbs).

Now lets say we are at a certain velocity where we could be in first gear (4:1 gear reduction) at 7000 rpm, or second gear (2:1 gear reduction) at 3000 rpm.

Now in second gear (most flywheel torque) we have 2:1 gear reduction * 300 ft-lbs of torque, or 600 ft-lbs delivered at the rear wheels.

In first gear we only have 300hp * 7000/5250 = 225 ft-lbs of flywheel torque, but it is multiplied by 4:1, so we have 900 ft-lbs of torque delivered.

Now it's obvious that 900ft-lbs at the rear wheel will accelerate you quicker than 600ft lbs, so first is better than second here.

So basically it's torque delivered, or the product of flywheel torque * gear multiplication that matters.


So what about horsepower?

We determined above that acceleration is determined by

Flywheel torque * gear multiplication.

Well what is flywheel torque - it is basically the rotational analogue of force.

What determines gear multiplication? Well, you have a fixed set of ratios in the tranny (not a CVT tranny) so what determines what gear you can be in? Velocity (road speed.

So in other words acceleration is proportional to

Force * velocity.

How convenient! There is an equation for power that says

Power = Force * Velocity!

So basically horsepower is telling us what the magnitude (proportionally) of the product of flywheel torque * gear multiplication will be - or at least when it will be maximized and minimized.

So if you maximize area under the hp curve, you are maximizing this product, and thus your acceleration. HP simply takes velocity into consideration (rate at which work can be applied), so you don't have to worry about gear ratio's, etc.

 

I guess there is always the concept of optimizing your gearing for your torque curve. If you run different gears in the L98 car you can make up some of the hp advantage an LT-1 has. But, there are also a lot of real life limitations to how you can set your gearing before it isn't as driveable anymore.

 

Another aspect of the gearing game, when optemizing your L98 for the 1/4mi, is to determine how long the motor spends in each RPM area. If you take an L98 with auto it spends most of it's time in the mid RPM range and secondly in the high end. For a 6-speed this would be a little different.

So you would most effectively put your $$ into mid range mods first and then into top end mods. Lingenfelter has a nice discussion of this principle in his book on SBCs. The more % of time you spend in 1st & 2nd the quicker you will get to the traps so raising the shift point is quite important too. If you can do this and build more mid-range torque you have the path.

 

One of my favorite explainations is at http:www.inv.net/davidstua. This is a home page. Find "Understanding horspower and torque there.

Another that I lost the address to with the death of my hardrive had the letters "Datsuns" in it.

However if you let your browser do the work and just type "horsepower and torque you will get a lot of pages on it.

The bottom line is that the best is a long, flat and high horsepower curve.

Torque means nothing without rotation or rpm.

 

Torque is the twisting force. Stick a torque wrench on a nut that won't move and you can apply torque [trying to move it] all day long but no work is done.
To get work (horsepower), you have to have displacement, something must move. Torque applied over any given distance in any given amount of time translates into work i.e. horsepower. Think of it like this; lets say you applied a constant 100 lb-ft torque to a nut that is turning. If you measured how far the end of the wrench moved in say one second, you could calculate the work (horsepower) done.
Hope this helps

 

Nobody mentioned my favorite: HP is the ability to provide torque at high RPM's. That's really what the equation is saying (HP=torque*RPM/5252), that for a given maximum value of torque the engine that reaches that torque at a higher RPM has more HP.

 

the short version of all this is TORQUE IS A MEASURE OF AN ENGINES ABILITY TO DO WORK. HORSEPOWER TELLS YOU HOW FAST IT CAN DO THAT WORK :yesnod: :yesnod:

 

I thought I had a grasp on hp and torque until I heard that you feel the torque curve and not the hp curve. When my L98 was stock, it seemed to die after 4500, not 3200. What do you think?