errr, that would be at low "rpm"

 

Torque is MEASURED
Horsepower is CALCULATED

without Torque, you will not have horsepower. therefore torque is more important then horsepower.

 

Everybody, pay attention to FCGuy. He undersands the truth of the matter.

 

Moving to car talk.

 

Both torque and HP are measures of the same thing except HP considers time. It is great to have torque, and better to have it at high rpm. But having a fatter power curve generally makes for better overall performance, even if the peak numbers are lower. This is a very narrow argument as there is a lot more to automobiles than these two measures.

 

the turning force of your wheels is measured in torque, HP is calculated from that. 3000 hp and 100 tq without the proper gearing will get you the slowest car ever made, a higher redline (and thus more HP) means you can run shorter gear ratios, which increases RWTQ, so essentially HP does nothing, redline, gearing and torque do it all.

 

[QUOTE]Originally posted by FCGuy
[B]I don't agree on the second part.

 

 

The analogy I use is 2 bicyclists, one weighs 100 pounds the other weighs 200 pounds. Let us imagine that for the sake of the argument the crank on the pedals is one foot long. When the 200 pound rider stand on the pedal he is exerting 200 foot pounds of torque the 100 pound man, 100 foot pounds of torque. In any gear AT THE SAME RPM the 200 pound rider is producing twice as much power.

Fortunately for the 100 pound man there are things called gears. Being light and wirery the 100 pound man can pedal twice as fast when he drops to a gear that doubles his mechanical advantage. The 200 pound rider being more massive can not generate the same pedal speed as the light weight quicker man. With the help of gearing the 100 pound rider by doubling his RPMs can produce the same power as the 200 pound rider.

So they are then equal right? No. The power to weight ratio obviously favors the 100 pound rider so the lighter weight engine (rider) pays dividends in having less mass to move. Consequently faster acceleration. The lighter weight also pays dividends in rolling resistance, braking, handling and even aero drag. Consequently higher cornering and top speeds.

As Colin Chapman once said "First add lightness"

All else being equal torque is a result of displacement. Tuned in an identical fashion a 4 liter engine will usually have twice the torque of a 2 liter engine. Where the F20C engine is an overachiever is that it produces about the right amount of torque for a 2 liter engine BUT IT REVS SO HIGH IT PRODUCES HP EQUIVELENT TO MUCH LARGER DISPLACEMENT ENGINES. Where people make their mistake is by comparing the engine to other engines with similar HP. There are no naturally aspirated 2 liter (production) engines with similar HP so the comparison ALWAYS results in comparing it to LARGER DISPLACEMENT engines. Of course the F20C engine won't have the torque of a 4 or 5 liter engine.

It also won't have the size and mass of one either. That is why the S2000 weighs what it does and the 350Z is heavier for example.

If "Torque wins races" then you would have guys like Arnold Swartzeneger winning the Tour de France not Lance Armstrong and they would be running Diesels in F-1 not 20000 RPM screamers.

You pay your money, you take your pick.

 

Lots and lots of ways to approach this. But I still have the feeling that maybe 50% get it.

(1) Empirical approach:
(1a) Most of you own S2000's. How can you not realize that it performs the same (accel-wise) as equivalent hp, not equivalent torque cars? [Caveat here and below: it is the power you are at, not just the "peak" number that matters. So, if you aren't going to rev it, you don't have the power, and it won't perform like a Mustang. But you all know that]

(1b) Look at the numbers in the back of R&T, MT, C&D, whatever. Graph accel vs hp/weight. You'll see a very consistent straight line with little scatter. Graph accel vs tq/weight and it'll show generally a straight line but with a bunch of outliers (diesels, big old pushrods engines, Hondas). The reason the tq has a reasonable fit at all is due to most engines are of similar nature. Generally they rev to about the same, and have similar shaped curves, thus the peak tq is a decent indicator of the pk hp and the general hp vs rpm curve. But the outliers prove the fallacy of equating peak torque to accel.

(2) Look at physics. The eqn's have been shown often enough that I won't show them again.

(3) Download a program such as Cartest and have fun with it. Make some mods to the program and see what happens. For instance, play with final drive ratio. Yes, increasing FD by 50% will increase the wheel tq by 50%, but the 0-60 or 1/4-mi gain is nowhere near as significant. Double the tq and halve the rpm and see what happens.

(4) Random argument that may annoy:
Sure, without torque you don't have hp. Sure, torque is "measured" whereas hp is "calculated". So what?

(5) Real-world example:
I can make 200 lb-ft of torque with a 2 ft breaker bar. Do you think I can accelerate an S2000 as fast as can its 153 lb-ft (at best!) engine??

(6) Okay, some math:
I'm going to seemingly contradict myself by pointing out the equivalence of both torque and hp approaches to understanding accel (though "equivalence" is a poor term to use. I certainly don't mean to say they are equal).

F=ma. So, if I want to accelerate a given mass m faster, I need more force. And since force acts on the wheel through the wheel radius, it is the wheel torque that generates the force. So yes, torque (at the wheel) matters and is what accelerates you. Torque at the wheel = gearing * torque at the engine, so the crank torque eventually is what accelerates you (well, not really since the gearing is as important). QED? Not so fast...

To accelerate a mass from V=0 to some final velocity V, I have to raise its kinetic energy by KE=0.5*mV^2. To accelerate quickly, I want that V, and thus KE, in less time. KE/time = power. That's the power your engine generates (minus driveline losses). So, power is what matters.

Inconsistent? No. If you do the math, as Destiny2002 showed, you'll see they are saying the same thing. And I am not saying that torque is as good an indicator of performance as hp. It isn't.

Certainly for the full picture, you need mass, driveline losses, gear ratios (but it is reasonable to assume that ratios are well-chosen for the application), launch method, inertia's, etc. But give me a car's peak hp, and its mass, and I'll give you a very good estimate of the accel. Give me just its peak tq and mass, and I'll be close only if my guess of the engine rev range is accurate (which means I am mentally estimating the hp).