ADiSKOTEC

I understand that the more of both, the faster you get going, but what do they really mean though? HP, a measure of power, and TQ a measure of turning force. How is it applied to a car? This is kind of a hard question to put together. I hope you guys understand what I mean.

Yes, the more torque at low rpm (or throughout) then the car can haul, but how does HP play into this?

no_really

HP is merely a calculation of how much torque an engine generates at a given rpm. The more torque at a given rpm, the more hp the engine makes at that rpm. You cannot directly increase HP, but by increasing the air pumping through the engine, you can increase torque over a range of rpm, and therefore increase HP over that range. Spinning an engine faster will generally not increase HP, as the engine will make less torque as the engine rpms climb above the torque peak, and at some point, usually near redline, the engine starts making less HP as rpms climb. Increasing torque is the way to increase your car's acceleration. Many people will make all kinds of justifications for their belief in HP numbers alone, but all the talk is merely smoke and mirrors obscuring the fact that HP is torque.

jerrypeterson

This link to "How stuff works" has some great explainations and diagrams.

http://auto.howstuffworks.com/horsepower.htm

Warren J. Dew

Instead of a "what they are" answer, I'm going to give you a "why they matter" answer.

Horsepower matters because that's how much power the car has, and directly affects the car's acceleration. Most manufacturers quote peak horsepower, since that's the biggest number.

However, since the engine operates over a range of rotational speeds, and doesn't necessarily make the same power over all of that range, it's important to know how broad the range is over which you can something close to the peak power. The broader the range, the closer you can keep the average power output to the peak output, and the less you have to shift to do that.

The torque peak helps define how broad that range is. The torque peak occurs at a lower rpm than the horsepower peak, and the range between the peak torque rpm and the peak horsepower rpm is often a good measure of how broad the engine's power peak is.

That brings up another issue: the most important number provided with the torque is not the actual peak torque number as much as the rpm at which that peak torque occurs. The lower the rpm of the torque peak, the better.

Of course, the best information comes from a dynamometer graph showing torque and power through the entire rpm range of the engine.

Palmateer

Good thread. Here's more, courtesy of Car and Driver:

Torque and Horsepower

The lb.-ft. is the English unit of torque, for example, of the twisting force produced by an engine

rai

I was wondering about this. So your peak hp is before red-line. So if you keep spinning past the peak HP does that mean you don't accelerate any more?

Also when you shift up (or down) your clutch engages your forward speed of the driveshaft will run the engine at a certain speed. So up-shifting at a higher speed should put your engine higher in the rev range. Would it be ideal to have the next gear engage near the TQ peak? Or does it depend on the type and size of the engine?

jigga009

It doesn't mean that you stop accelerating.. You do, but at a lower rate than you were prior to the HP peak. The advantage of reving past the peak though is that it puts you close to it in the next gear, thus enhancing acceleration in that gear.

skittzomaniac

not necessarily. look at the dyno plot for any centrifugally supercharged car. the s/c doesn't make full boost until the instant before redline. pk torque also occurs slightly before redline. that means pk hp occurs AT redline, not before
example taken from this website:



pk hp is a better measure of power/speed than pk trq; pk trq is about the most meaningless stat there is for cars. whats important than both of them is the trq curve. with the same driver, the car with the most area under the trq curve wins the race, period. (all you engineers out there know thats the integral. )

hp is, has been, and always will be a calculated value that cannot be measured. dynos measure torque and calculate hp. tune your trq curve and the hp will come.
another interesting point: as already noted: hp = (trq*rpm)/5252. so, on any car, with any mods anywhere at any time on any dyno, trq will ALWAYS equal hp at 5252 rpms, per the equation.

gomarlins3

Discussion from another site:
http://fresnoracing.ipbhost.com/inde...showtopic=8374

steven975

I don't totally agree with this. while the peak RPM is valuable info, an engine that makes very consistent torque yet peaks at 6000rpm is way better than one with similar torque that peaks at 3000rpm.

the key word is consistency of the torque, or the "flatness" of the curve.

many domestic guys think torque is everything. i disagree. you can have an engine with gobs of torque, but if it can't make torque at a decent rpm, the acceleration is poor. take the 5.0 stangs...300 lb-ft, but only like 200HP. those engines simply could not make torque high up.