HP vs TQ Which is King?

[WestTexasS2K]

My buddy Kevin sent this tech article to me thought it would be an interesting read for the members here. I cant seem to get it to post but this is the address. If someone knows how to post it please do.

 

 

 

   http://www.v8914/Horsepower-v-torqueWestTexasS2K2007-01-29 07:02:22

[slngsht]

The address says http://www.v8914/Horsepower-v-torque

 

Seems like an incomplete address

 

 

[slngsht]

found the correct link

 

 

 

>http://www.v8914.com/Horsepower-v-torque.htm

[WestTexasS2K]

Thanks for the help I cant seem to get things to post for some reason. I tried to copy and paste the page but it left the charts and drawing off. Thanks for doing the link.

[slngsht]

I agree with some of his conclusions, but here are some thoughts, as they apply to the way we actually use engines.

 

1- if engines were used in steady state, like with a CVT, where the engine runs at its peak efficiency range (in either power or fuel consumption), then he is right... HP is king, and peak HP is all that matters, because that's where you run.

 

2- Since for most of us, that is not the reality, and we actually use the engine throughout its dynamic range, things besides peak power matter. One running joke on this matter is: What do 1000 hp supras have in common with 400 hp supras? They both run 12's in the quarter http://www.usa7s.com/aspnetforum/images/emoticons/biggrin5.gif. The reason people say this exaggeration is because the power produced is very peaky, so the area under the power curve is smaller than comparable engines that don't produce as much peak power.

 

 

 

So, which is king, HP or Torque? Depends on the application. For a race car, where you're sawing at the stick all the time to keep the revs in a 2000 rpm window, peak power is what matters. For the street, it's neither - to me for a street car, the king is the area under the power curve. That's what gives you good driveability, and performance. By the time a high HP car works its way up the power band, or does the downshift, the guy with the broader torque curve (same as the power curve in concept) is long gone.

 

Also keep in mind, cars with flatter curves are easier to handle when powering out of corners, etc...

 

One more thing on this subject. When you look at curves for stock LS1s, etc... you notice peak torque is quite low, and it drops steadily throughout the rpm range. When you install aftermarket cams, they knock down low rpm torque, and put it more on the high rpm range, hence more power. The reason manufacturers don't do it this way is driveability (besides emissions concerns, fuel economy, etc...). Imagine going constant speed down a highway, and the road starts on a gentle hill. The engine with a fatter torque curve on the bottom does a much better job of maintaining speed, because as engine rpm drops, it produces more torque, requiring less of a correction by the driver.

 

Damn, I wish I could write like this on the business proposal I'm supposed to be working on... I should change careers - seriously

[xromad]

Actually that was an excellent article. Very good research.

 

 

 

However, It misses two important parts of the equation. The first part of the equation is area under the curve. The second part is driveability. Both of these are more a function of torque than a function of horsepower.

 

 

 

Car engines don't have the luxury of always operating at peak horsepower. Like it or not, they are required to accelerate, slow down, stop, and otherwise work within a fixed set of 3 to 6 gears. Quite a number of real race car transmissions only have 2 gears.

 

 

 

The first part, area under the curve takes into account the ability of the motor to work within the gear set that it has. It will only be near peak horsepower for a few hundred RPM. Therefore it is vitally important how the engine behaves when it is not at peak horsepower. A big broad torque curve helps the car accelerate over its entire RPM range not just for the few feet that it is near its optimum.

 

 

 

Example: Autocrossing - I can come out of a fairly tight corner in third at around 2k rpm. At that point I can generate around 160ft lbs of torque at WOT (60hp). I can then accelerate so hard that I have to feather the throttle in order to keep the tires hooked up. (i.e. I am generating more rear wheel torque than the car can effectively use) I accelerate all the way to the next corner where I arrive still in 3rd at around 6k rpm and around 160ft lbs of torque (180hp). Along the way, I passed my peak horsepower at around 5500 rpm where I was generating almost 200 ft lbs of torque (209hp). With that big flat torque curve, I was able to accelerate almost as hard as my maximum all the way from 2k to 6k and didn't have to shift once.

 

 

 

This is closely related to driveability. I have driven a couple of cars that technically had a cubic shitload of horsepower between 7k and 8k rpm. But trying to get them rolling from a stop sign just sucked. Slip the clutch, kill the motor. Slip the clutch more, burn the clutch.    Launch and let the tires take the abuse and get a ticket from the local cops. Take it to the track and it can be just as bad. Below the power band, the accelerator pedal is nothing more than a wish list. In the peak power band you are fine until you have to use the throttle with finesse, then it behaves like an on/off switch. Too much, oops throttle oversteer, too little, oops trailing oversteer. "Dang that thing sure is twitchy!"

 

 

 

So, to answer your article: Yes, you are absolutely correct.

 

 

 

Horsepower rules.

 

 

 

But, As a single tuning goal it only pays off at drag strips, Bonneville, and some long road races. However, most tracks, all autocross, and all street driving, it is far more important to have an engine that has a broad flat torque curve that is easy to manage. This lets you power out of a tight corner near the bottom of your rpm range, blast down the straight to the next corner, dive in and do it again. Now that's what I call fun! http://www.usa7s.com/aspnetforum/images/emoticons/coolgleamA.gif

 

 

 

Brent