JustinL

Try this one. Totally unrealistic, but interesting anyway. To get linear force, you just multiply the ratio by the torque for each gear.

Car A
150 ftlb across the entire range (0-8500RPM)
240 hp at max 8500 RPM

Car B
240 ftlb across the entire range (0-3300RPM)
150 hp at max 3300 RPM

Both cars are otherwise equal in mass (3000 lbs) and gearing and tires:
1st gear ratio at the wheels: 12:1
2nd gear ratio at the wheels: 6:1
3rd gear ratio at the wheels: 3:1
Both start from a dead stop and accelerate to the end of 3rd gear.

jimbo1111

A motor that will have an equal amount of hp and torque will be the best performer. When you have equal hp and torque the area between the 2 is always wider and sustained for a longer period.

Chris White

If you want to find the answer you need to look at the torque curve and gearing. A single measurement at a given RPM will not give you enough info to figure it out.

The force that accelerates a body is torque – to make a comparison between different vehicles you need to figure the torque at the contract patch – this is engine torque multiplied by the transmission, rear gear and tire diameter (to get a real comparison you need to divide that by the weight of the vehicle). Run you comparison at different speeds and you will see which vehicle applies more force to the road.

Chris White

aeronautica86

not really true, horsepower is torque applied over time, and due to resistance (ie friction, air) and force (measured by tq at the wheels) is needed to overcome resistance at speed

RKD in OKC

To answer the original question of which car will win one with high hp or one with higher torque.

Think of it this way. When accelerating a car you are not accelerating it over the rpm range of the engine, you are accelerating the car over the rpm range of the rear wheels.
A dyno chart plots torque of the engine over it's rpm range and not the wheels rpm range. That's why it is done in the gear closest to a 1:1 final drive ratio. The tranmission changes the torque of the motor as it applies torque to the wheels/ground. Generally lower gearing increases torque, higher gearing decreases torque.

In acceleration, the car will be the fastest that puts the most torque to the ground over the rpm range of the wheels.

Alpine951

I think torque is what matters. Also if it is constant then thats what is truely important. This is what is meant by the term area under the curve. Having a broad or flat torque curve that doesn't drop is what it is all about. Peolpe talk HP HP HP. I want torque. ANd I want a relativley good torque that stays as constant as possible. Peak torque isn't too important unless the peak torque is 1000# and drops to 800#!! HP is just a measure of how much torque is generated over the rpm band.

SoloRacer

I have used a shareware program called cartest 4.5 that works pretty good at comparing different cars. It even lets you change a bunch of the parameters on the cars so that you can compare how a 300 hp/200 lb-ft car would compare to a 200 hp/300 lb-ft car of the same make and model. It simulates standing start drag races as well as famous race track lap times. Want to compare your 951 to a Ferrari Testarossa? No problem. How about set up a drag race between a Viper, Z06, BPU Supra, Formula 1 race car and your 951? No problem. Want to see what different gearing will do to your cars performance? No problem. It's a pretty cool program actually and it seems to be fairly accurate. It's shareware so it's free with the option to send the author $20 if you like it. The link is:

http://www.cartestsoftware.com/cartest4.5/index.html

Enjoy!

944CS

the relationship is purely mathematical. Horsepower is derived from the equation Hp = (Torque x rpm)/ 5252. (That is why your curve should always cross at 5252 rpm). Horsepower is defined as the power needed to do 33,000 foot-pounds of work per minute. While Horsepower is a linear measurement, torque is a rotational force applied to a body (from crank, to flywheel, through driveshaft, to trans, to driveaxles, to wheels).
The reason cars make more horsepower than torque at higher rpms than 5252 is because the number of rpm's the engine can spin above 5252 is greater than the loss of torque at those higher rpms. For example, and engine makes 400 foot pounds of torque at 5000 but only 350 at 6000. Plug the numbers in. That loss of 50 foot pounds is more than offset by the additional 1000 rpms the engine spun.

Duke

Yes as some say, torque is what "matters" but when it's not coupled with rpm's its useless!

Imagine 2 engines with the same powerband. Both make peak power of 200 hp. One makes it at 10000 rpms and the other at 5000 rpm.
The one that spins 10000 rpms will have half the torque of the 5000-rpm-engine.
But it doesn't matter because the high-rpm engine turns twice as fast and hence create the same usuable power.

As said, peak numbers doesn't say much, you have to looke at whats available throughout the used powerband. BUT, if you want to look at peak numbers, peak HP is a lot more usuable than peak TQ if you want a fast car.

Duke

HP wins every time. And this is much easier to understand in Europe where we have a lot of diesels cars

TurboTommy

There are other threads in the past that cover this. It has been discussed many times, but it still seems to be hard to understand. And it IS hard to understand; it took me awhile before I grasped the concept.

Like Duke (and maybe others) have said; the only thing that matters is horsepower. Technically, and mathematically the torque figure is useless; it will automatically be reflected in the hp figure anyway, because of the above mentioned formula.
Understanding how gearing works is absolutely essential because it works with your engine characteristics to get the power to the ground.
Example (as already stated): high hp, low torque will rev high and will have shorter gearing (higher ratios). These higher ratios will multiply the so-called lower engine torque number into a larger number by the time it gets to the contact patch (the only place the torque/power gets used).
Therefore the only thing that matters is the hp number.

However, the other issue, which is significant, is the RPM spread between the peak torque figure and the peak hp figure. This will be an indication of the usably width of the power band, or area under the curve. Note; the actual torque number is insignificant.
The larger the spread, the faster the vehicle will be (given two vehicles of the same power) because of the engine's (and, therefore, the drive wheels) longer duration at higher torque levels

A.Wayne

Could not agree more , but i want some RPM with that HP.
HP and RPM beats torque everytime , unless the race is for the first 60 ft.or pulling your car trailer .

mark944turbo

HORSEPOWER WINS!!!!!!!!!!!!!!!

TurboTommy

"but i want some RPM with that HP"

That's a confusing statement.
250 hp is 250 hp. It doesn't matter at what RPM it gets made!

If anything, it would be slightly better if it got made at a lower RPM. Lower RPM engines generally (but, not always) have a greater spread between peak torque and peak hp.

Laust Pedersen

HP (Power) has a direct relationship to acceleration since it is energy delivered per time. The amount of energy needed to go from V1 to V2 (speed) is E2-1 = ½ m*(V2^2 - V1^2) and the amount of Power needed to do this in x seconds is E2-1 / x (wind resistance not considered here). When knowing the rpm/mph for each gear, the HP curve even tells you when to change gears for optimum acceleration.

The only challenge is to keep the rpm in the range of peak HP, which for torque-challenged cars typically occur away from cruising rpm, meaning that max acceleration is not instantaneously available for regular street-driving, much like our turbocharger lagging characteristic. For racing it is not a problem … except for the compromise between burning a clutch and stalling the engine when leaving the pits.

Laust

PS The formulas are a little clumsy without sub- and super-scripts.