Torque vs Horsepower -- how do you use it?

**RafRaf** · April 28th, 2004 09:17 AM

hmmm... on humps, I usually thift down to third (speed down to 10-15kph) and slip the clutch a bit (so as not to lug the engine) then get back to speed... hindi naman masyadong hirap ang engine ng adventure (diesel) ko. Is that ok or am I wearing of my clutch too soon?

**racerx** · April 28th, 2004 10:46 AM

afaik you should go down to 2nd at least

**wiretap_md** · April 28th, 2004 11:23 AM

H for horsepower = Honda
T for torque = Toyota

**trisky** · April 30th, 2004 02:30 AM

Ang power po ay product ng torque at angular speed.
Units for power are Hp, kW etc.
Torque units naman are in N-m, ft-lbs etc. (perpendicular force x distance ~ to create a turning effect called moment)
Units of angular speed naman po ay rad/sec, rpm etc.

Do the maths from here... hehehehe....

Ang ibig pong sabihin nito, at a certain rpm, power is directly proportional to torque, i.e., the higher the torque, the higher the power, or vice-versa, the higher the power, the higher the torque.

So if you look at torque-speed curves, you'll notice that power is not mentioned. Simply because it's the product of torque and speed at a point in the curve. If you know the torque and speed at a point, you can calculate the power requirement at that point. Just make sure your units are consistent.

Boring huh?

**ebbfolls** · May 2nd, 2004 12:22 AM

I also got purdy confused about this some time ago and all the books, magazines, etc, that Ive read about it on didnt give me a clear understanding of what torque and horsepower really were. Most of them said torque was the twisting force and horsepower was the ability to do work in a given time. That made sense, but there was something that still didnt make it all fit together. So I tried figuring the formula for horsepower. HP = Torque X RPM/5252. And that's how I think I've finally figured out the basic truth about the whole thing:

Torque, as how the word is mostly used, means the twisting force, which ultimately translates to "hatak".

Horsepower simply means Torque X RPM/5252, thus if it is said that an engine has a high horsepower rating, it either means it has a lot of torque at a low rpm (e.g., large displacement diesels as used in commercial trucks or in marine application) or it is capable of very high rpm though it can only produce relatively little torque(e.g., racebikes, small displacement/high HP cars like the Honda S2000), or both(like the large displacement, high HP engines found in expensive sports cars/sedans).

So when a layman says a car is "torquey" it usually means the engine produces a lot of torque at low rpm(Low RPM Torque). (Ever notice how this characteristic is strong among diesels? Well that's because diesels are designed to breathe efficiently at lower rpm by reason of the slower burn rate of diesel fuel. It's just much harder for a diesel engine to burn a charge efficiently for a period of .005 sec, which is the time the entire power stroke takes from TDC to BDC at 6000 RPM.) In contrast, a high HP car would be relatively weak at low rpm but would suddenly feel strong at mid to high rpm(High RPM Torque). This characteristic of the engine is all a part of engine tuning(intake/exhaust design and valve timing)--which basically addresses the question: at what rpm do you want your engine to be strong at?

Low-End torque and High-End torque both have pros and cons which I need not explain further. To get the best of both worlds, engineers have come up with techniques that allow the engine to breathe equally well at all rpm's. There are 2 basic was to do this: Variable Valve Timing and Variable Intake Runners.

To conclude: "torquey" means the car is STRONG, while High HP means that the car is FAST.

**ebbfolls** · May 2nd, 2004 12:35 AM

Originally posted by wiretap_md
H for horsepower = Honda
T for torque = Toyota

LOL! That's a good observation. It does hold true for the most part.

**ebbfolls** · May 2nd, 2004 01:18 AM

Originally posted by luckytruck
as far as i recall, someone on this board said that in order to accelerate in the most efficient manner (not waste any engine force), shifting should be done at the rpm where there is the max torque. anything above that, you are just wasting energy. tama ba yon?

andy

That depends on what you mean by efficiently. If you mean efficient as in the quickest way to accelerate, theory dictates that you shift up ONLY at the roadspeed that will cause your next higher gear to spin the engine at the rpm slightly lower than the rpm where it is making the most TORQUE. Fpr example, if your car is running at 40 mph and the engine is spinning at say 5,500 rpm in first gear, and that 2nd gear at 40 mph vehicle speed would spin the engine at 4,200 rpm, while peak torque is found at 4,500 rpm, then yes 5,500 rpm is your most efficient shift point when shifting from 1st to 2nd. If you upshift from 1st at 30 mph, the engine would only be spinning at 4,125 rpm and would then translate to 3,150 rpm at 2nd gear, which is way below the 4,500 rpm at which max torque occurs(depending on the torque curve characteristic of the engine, this may not be too bad--but if the engine is "peaky" it would really make a big difference).

On the other hande, if you mean efficient as in frugal, then it would be best to shift at the vehicle speed that would allow the engine to spin at an rpm enough for it to make the torque required to move the car in the next higher gear. The engine is operating at its leanest at the least amount of throttle opening for a given speed and load. So, in order to be fuel efficient, one needs only to push down on the accelerator gently and shift up soon enough as to allow the engine to pull the car without need for excessive accelerator pedal pressure(which may be accompanied by knocking).

**RafRaf** · May 3rd, 2004 02:04 PM

trisky, ebbfolls... learned a lot from your posts... I see the light... thank you!

**Vegeta** · May 3rd, 2004 02:26 PM

torque.....ya'll need it kung naghahatak kayo ng farm trailer.
I should have got me a diesel kung alam ko lang na ganito magiging trabaho ng truck ko

**ebbfolls** · May 4th, 2004 09:03 AM

Originally posted by xox
i still don't get it btw, is torque like acceleration which measures speed without the weight of the car or is it more like horsepower where you have to take into consideration the weight?

I mean a 0-100 7 sec. car is as fast as a 0-100 7 sec. truck, however a 200 horsepower car should be faster than a 200 horsepower truck keeping everything else other than weight similar. Which is torque more related to? Will a 500lb-ft car be as fast as a 500lb-ft truck?

I just noticed your post.

When you involve weight (more appropriately, MASS) when talking about power and torque, you are in effect talking about "POWER-TO-WEIGHT RATIO", which is the one and only determinant of HOW FAST CAN YOUR CAR ACCELERATE, aside from traction.

Referring to your question, it is obvious the 500 ft-lb car will easily out-accelerate the 500 ft-lb truck because it is much, much lighter. In fact, a car with an engine capable of 80 ft-lbs will still out-accelerate the much more torquey truck by reason of the much lighter load it has to accelerate. This is one of the reasons why sports cars are deliberately designed to be light. The other reason is very similar, and that is, a lighter car will much more easily change speed and direction.

As you may already have read, Horsepower is merely Torque multiplied by the RPM and divided by the constant of 5,252. Horsepower and Torque have nothing to do the weight of the car they will be accelerating.

Rafraf: You're welcome, Sir.