Mikestro

http://www.yawpower.com/tqvshp.html

He has math to back up his claim, it is a good read. Sorry if it is a repost.

Nismobilized

Resembles my physics book, lots of examples.

Nice find, i learned a lot.

Mikestro

"So there it is. Horsepower is the determining factor in the rate of acceleration of any vehicle. "

^This is the summary of the article. I probably should have included it with my first post.

boyze

yup. But only for the same weight(mass), rotating/translational weight ratio, drive train loss, drag coefficient, tire rolling resistance, power vs rpm curve, environmentals(temp, air density, humidity) and lets not forget that ever important driver factor

350zdanny

Awesome article. Thanks for posting it. I never really took the time to derive the HP formula before. It was very rewarding.

Dan

Xeinth

There is one 'problem' as I see it from that article.

First as stated:

Horsepower equals torque times rpm divided by 5252. Horsepower = (Torque X RPM) / 5252

Torque equals horsepower times 5252 divided by rpm. Torque = (Horsepower X 5252) / RPM

RPM equals horsepower times 5252 divided by torque. RPM = (Horsepower X 5252) / Torque


This means that, for the same drivetrain, two engines with the same HP curves, will ALWAYS produce the same torque. ALWAYS. Thus, HP and Torque are the same measurement in many respoects. Torque is the transformation of HP to the wheels, given a particular gear ratio.

How I find this to be particularily intersting is that a given mod which increases HP by a given amount, must always raise torque by a porportional amount. For example, at one point I remember people saying that the XERD heards made 17HP, but little torque. Well, if we assume that the 17HP is near redline, say 6000RPM, it should have made 17*5252/6000 = 14TQ EXACTLY.

At least, if you believe that article.

X

Mikestro

I thought the issue was the Xerd headers didn't make much torque at low RPMs.

Anywho, if you dig up the dyno you are referring to (or any dyno) it is easy enough to validate the HP/TQ formula. I have done this in the past, it holds true as near as I can tell. First sign of fake dyno is HP and TQ not crossing at 5252 RPMs.

Silver Bullit II

Well, yawpower is partially correct, yet fully a moron. Not that simple. The debate goes on...

http://vettenet.org/torquehp.html

Xeinth

SilverBullet,

That link was much more logical. That explains the problems I found with the first one. Thanks!

It makes more sense that acceleration follows the torque curve anyway...

X

350zdanny

Xeinth -

I understand what you are saying, however what you quoted from the yaw article is just a manipulation of a proven formula. The basic physics of both arguments are still the same.

Dan

AndyB

The difference is that high torque engines are probably easier to drive well. With a high revving, hi power, low torwue engine (RX-8 / S2K) you really need to keep the revs up and keep the engine in the sweet spot for best results.

An engine with a broader power curve (more torque, particularly down low) is more forgiving if you shift to early or simply choose not to run to redline every shift.

I am not saying the article is wrong. I am just saying that a car with low end grunt/torque is (to me) much more satisfying to drive and much EASIER to drive quickly.

Andy's addendum: Horsepower wins motor races, torque produces motor grins.

FLY BY Z

How about,

Horsepower raises the dyno, torque raises the butt dyno.

Xeinth

Not bad... not bad...

X

ares

iTrader: (2)

its all about area under the curve; screw the formulas. get jiggy with some calculus and derivatives. peak hp means nothing; same for peak torque. its all about total area under the curve.

also why it might not be beneficial to shift at redline. you have a 1500RPM window give or take in each gear. go from 3000-4500, shift, back to 3000. you want that 1500RPM to have as much air under the dyno curve as possible. words and formulas are great for text book talk where the favorite phrase is "assume"; always making thing into the perfect world. and assuming you accelerate at a point, not a band.

to use real world models for a moment; this is why the Z is more rewarding around town; you assume you will be shifting at 4000RPMs and dropping down to 2000, comparing the dynos of that area to a S2k or the like; you quickly see WAY more area under the torque curves on the Z. but when you get up into the racing area; you see the S2k has lots of hp. much of its extra hp comes from the fact that it can multiply its torque by a higher RPM to yeild a higher HP. not that its cheating; it works.

just find that articly, tho informative, a bit ignorant to reality. at some point you need to put down the physics book and realize the world isnt perfect, and dyno plots arent straight lines.

if every engine didnt have a point to its existance; it wouldnt be produced. not that torque doenst matter like that article seems to lead you to beleive. if he was smart he wouldnt argue torque doesnt matter; he'd argue that weight does; and the sacrifice in power is worth the improvement in weight.

Xeinth

Torque generates acceleration, HP is really just an effect of the RPMs, and in many respects is the artifact of the torque and gearing.

Remeber, F=MA. So if you want to accelerate faster, you need more force at the wheels, which is the definition of torque. Period. Everything from acceleration to top speed is a function of torque.

X

ares

iTrader: (2)

I beleive dynos only measure torque as well. hp is just a curve calculated by inserting the torque curve into the equation.

Xeinth

Ares,

Exactly. You cannot measure power directly. You must measure the work done. Power equals work divided by time (P=W/t). Work is equal to a force times a distance(W=Fd). Thus P=F*d/t, where d/t is rotational velocity, directly related to the RPMs. You measure the force on the dyno (torque). Then once you get the RPMs you know the distance and time to caculate rotational velocity, and then power.


You can have all the HP in the world, but if you dont have the torque to turn the wheels (i.e. exceeding friction), it wont do anything.

X