I am posing a question out of curiousity
What would be the differences( performance- wise, advantages v. disadvantages etc.) between an engine with a torque rating higher than it's horsepower rating and on the other hand an engine with a horsepower rating higher than it's torque rating?

Torque is what will bend 1/2 shafts, driveshafts, etc generally tear stuff up, horsepower is defined as the amount of energy required to lift one pound in one minute or something like that.

When it comes to cars it is the horsepower that makes you go faster (top end) and the torque gets you there. Watch a drag race and you can see examples of these terms.

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Jim

A good example is the Humvee. it has something like 175hp and 490 ft lbs of torque. Not a speed machine by any means (although I hear they can top 90mph) but the torque will push them through, over or around anything.

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Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired

Howdy All
And a bad example;404 Mog 90hp & 120ft lbs of torque for a 6600 lb. vehicle

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Frank X. Morris
17 Kia Niro
08 Jeep Wrangler 4 door unlimited

My bmw has 121hp and 170 ft lb. it just makes it seem like the car is getting a burst of power of the line at least I think

Torque and horsepower are not unrelated.

They are related to each other as Power = Torque times Rotational Speed.

If HP, RPM and ft-lb are used as units, then the calculation is

Horsepower = (Torque)(RPM)/5252

It takes torque to rotate the wheels. It takes a high power to rotate the wheels fast as you can see from the equation.

Here is a reference Website:

http://vette.ohioracing.com/hp.html

I've seen it paraphrased in a car magazine a while ago, and it went something like this:

"Torque is a measure of the amount of horsepower available at a given rpm".

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Sometimes ago,I have read this.Under square engine,(higher
torque less hp.)rev lower.Some people called it lazy engine.
Over square engine (higher hp. less torque)are design to
have a higher redline.They called it screamer.
Examples:Benzman's car 121hp-170lbs.ft of torque=4,800 redline.
Acura NSX 270hp.-209lbs.ft of torque=7,800 redline.

Great topic.

I like these descriptions and thought processes. Based on the mathematical relationship between torque and horsepower, I've always thought of big horsepower numbers as "the ability to continue making decent torque at high RPMs". Because given a flat torque curve, the horsepower will continue to climb. It peaks when the torque falls off.

Here's one I've always pondered, but I admit I haven't done the math to get the answer:

Q: For maximum acceleration, would you want to be at the peak of the torque curve or the horsepower curve? Would your answer change depending on the weight of the vehicle?

I think I'd want to be at the peak of the torque curve for any weight vehicle. That theory would mean that once your torque starts dropping it's time to shift, even if there's a lot of RPMs left with big horsepower numbers up at the top.

Other theories?

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D.H.

04 ML500
02 E430

Experience is something you don't get until just after you need it.

They bmw has a 5k red line( soon 5,500) I can verify that (drives me crazy your at the top of the gear real quick. But I also get great mileage when it runs.
How about the 500
245hp
295ft.lb. redline was at 6k I think on it

Here's what i dont understand.
People say "hp sells cars, torque wins races", its also widely thought that torque is good for fast acceleration, hp being useful for high-end speed.

So why do low-hp, high-torque diesels accelerate so damn slow?

Is there another factor involved here, am I understanding this wrong, or are the previously mentioned statements simply false?

Trelinski,
a very good question, which has also occured to me (btw, i'm in ajax, west of you)

Ultimately, it is power that matters, to overcome interia, internal friction and aerodynamic drag, at a given engine speed (i.e., torque applied at a given rpm is power). Most diesel engines have a low HP rating because of the low redline, because traditional diesels are not particularly effective at high rpm. And horsepower depends on torque AND rpm.

One missing factor is gearing. However, because of the diversity in gearing of cars, it is difficult to compare high-torque and high-hp cars. (other factors are vehicle mass and aero drag)

Instead, one could imagine a hypothetical car that had a continuously-variable transmission (CVT - like that in the new Audis), and where you could easily swap engines: to get the max acceleration, you would run the engine at the HP peak and vary the drive ratio continuously. If you had a diesel engine and a gas engine with the same power and weight, they will produce the same acceleration. In any case, an engine with a lower HP rating would produce a lower acceleration.

A counterexample to slow high-torque diesels is a semi-trailer truck without the trailer. With an 18-speed transmission, you could launch it from a stop in one of the middle or higher gears, producing an acceleration that will humble some cars. The gearing of the higher gears is being used to take advantage of the vast reserves of torque that are not being used. They race these trucks in Europe!

Ya mercedes has a game in german you can race trucks in.

Hey Bobbyv, what do you drive, maybe I've seen you around?

In all honesty, I still cant fully comprehend the torque/hp concept, maybe it will come in time.

Trelinski,
i drive a 5spd 190e2.6. I rarely go east of Ajax, and park at the Ajax Go Train station since i work downtown. (But sometimes i go to Oshawa to exercise my car and explore the M103's torque characteristics in 3rd gear on the onramps )

The concept of torque is quite abstract, but i have the following electrical analogy: torque is like voltage, and RPM is like current. Multiplying the voltage by the current, you have power (watt = volt-ampere). Except in an engine, both the torque and the RPM vary.

A flat torque curve is the ideal one - having constant torque across the entire RPM spectrum. In this case, the power curve will be linear with RPM.

But torque in an internal combustion engine is influenced by a number of factors across the RPM range, and therefore it is exactly that - a curve. The realistic objective is therefore to have as much torque as possible as low as possible in the RPM range above idle, and to maintain this across the "sweet spot" of the designed engine operating environment. For typical daily driving, this is around 2000-4000rpm. Having at least 80% of the max torque in this sweet spot, for example, makes the power "usable" for daily driving - you don't have to rev the engine high to get torque. Designers resort to variable valve timing and variable induction, among others, to "flatten" the torque curve.

A racing engine on the other hand, is designed to make full use of its redline (they say that RPMs are free). The power and torque peaks are typically high in the RPM range, close to each other, with little attention paid to low-rpm torque (look at the Honda S2000 figures). The induction system, exhaust system and valvetrain (e.g. VTEC) are all tuned to maintain the torque high up in the rpm range. Close-ratio transmissions are typically used, so that the RPM stays within the sweet spot when you upshift or downshift.

i hope this did not make things more confusing.

may the torque be with you ...