Re: tourque versus horsepower

Hi,

> Let me explain it in simple terms. Torque is how big a stump it can pull > vs. Hp is how fast it can pull. How is that?

I prefer to think of it in terms of driving nails into a piece of wood.

- Torque is how hard you can hit a nail.

- HP is how many nails you can drive into the wood in a minute.

Gearing is how you convert HP into usable power. Given the appropriate transmission it doesn't matter what the torque is. .000001 ft/lbs of torque can pull a boat up Mt. Everest given high enough RPM and low enough gearing.

Reply to
Cam Penner
Loading thread data ...

Chrysler says the T&C only weighs 4200 lbs.

Reply to
Ian Firth

This is a very complex issue.

The power and torque figures are only a starting point as to how a car fast a car will feel. It depends on where in the rpm range the torque and power is made and how flat the torque and power curves are.

An engine making 150hp at say 6000rpm and torque of say 150ft lbs at

4000rpm could be said to be peaky and needs to be revved to get the best out of it. An engine making 130hp at say 5000rpm and torque of say 130ft lbs at 3000rpm may have less power and torque but feel faster because it reaches these figures earlier in the rev range and maybe have a flatter torque curve thus the torque at lower revs may even be greater than the engine with a higher peak torque. Most of the daily driving we do is in the torque range and unless you rev the motor power doesn't really come into the equation.

This is why V8's feel stronger than a 6 with the same amount of power as the V8 has more torque or low end grunt and is usually developed earlier in the rev range.

It can be disasterous to buy a car just by purely looking at the power and torque figures in isolation. Things that affect the way a car drives include but not necessarily limited to the following:

1) The amount of torque 2) the torque curve and how flat it is 3) where in the rev range the torque peak occurs (although with a flat torque curve this is almost irrelevant... read turbos usually have flatter torque curves) 4) power output 5) the power curve and how flat it is 6) where in the rev range the power peak occurs (although generally the more power you want an engine to make you need it to rev higher) 7) gearing (how this interacts with the the power and torque curves and the weight of the vehicle) 8) vehicle weight

Sure, look at the torque and power figures but also look at where these figures in the rev range occurs and better still see if you can get power/torque GRAPHS which show the curve. Most of all drive the vehicle before you buy and compare this with you graphs to see how it all interacts.

Reply to
Lance B

In mathematical terms, HP = torque times rpm. That equation gives the link between HP and torque that you were looking for.

Since, at a given point in the drivetrain (engine or drive axle), ignoring friction losses, the HP is the same, you can also invent your own unit (call them Tonyramas, or TRs) for comparing one scenario with another by multiplying by PI x D, where D is the effective OD of the tire. This essentially means a TR, which is proportional to HP (at the wheel), is torque times the linear distance traveled by the vehicle (assuming no tire slippage).

The link between weight (total vehicle and cargo) and torque is the familiar *F*orce (tangential force of the tire on the road, which is Torque x PI x D) = *M*ass (vehicle + cargo) x *A*cceleration (of vehicle and cargo in a straight line). If you combine the equations, you can tell, for a given cargo weight and HP at the wheel, what your acceleration will be.

Maybe you are seeing now that the weight carrying ability and HP are really not directly linked. All you know from those two inputs is what the vehicle acceleration will be.

This is the kind of thing that you should set up in a spreadsheet for comparison of scenarios. It will take a little mental energy to set up your formulas, but once you have that work done, you just plug in the numbers and let the spreadsheet spit out the answers for comparison.

As the others stated, in practical terms, you can see how the speed factors in. You can be going at zero mph in which case with a lot of force, in which case, with no slippage, no HP is being seen at the wheels (the stump-pulling example that was given). Also, if HP were constant regardless of speed (which it isn't), the faster you go, the more you lose torque and acceleration.

HTH

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

I would aslo add to Lance's fine post, AT vs MT and throttle response(lag).(I miss carbs.)

Carl

1 Lucky Texan

Lance B wrote:

Reply to
Carl 1 Lucky Texan

I won't even try to explain, others have already done it better than I ever could...

It would help if you gave a bit more information on your car. For starters, is it a stickshift or an automatic?

Have you tried pulling 900 lbs. with it?

What kind of engine? A V6?

Again, manual or automatic? If it's an automatic, could the transmission be slipping? If it's a manual, are you using it efficiently?

What you're missing is the engine rpm where these figures where obtained. Get this and then go out and do the test. If you need to rev your Subaru at 4000 rpm or higher to make it work and you drive it at

2000 rpm like your mother's V6 van, of course you'll find it slow: you're lugging the engine.
Reply to
powertrain

don't forget the big one--your subie is awd. you lose a lot more power in drivetrain losses and end up putting less power down to the wheels.

to go along with what the other posters said, keep in mind what actually moves the car forward is the AREA under the HP vs RPM curve.

ken

Reply to
Ken Gilbert

Amen to that! Maybe I just haven't driven the right cars, but I've yet to find a computer controlled fuel injected engine that responds as quickly as a mechanically injected or carburetted engine. It's probably more a "feel" thing than something that proves itself out with numbers.

What others have said about the numbers is all good, but I think the most important thing anyone said is to learn to drive the particular engine/gearbox combo. IME Subies need to be kept wound up to do anything, so a person who's timid about opening the throttle and watching the revs climb on the tach's gonna get less "performance" out of his engine. I have a buddy who drives big V-8's in his pickups who has a fit every time he rides with me and sees the needle hit the "5" on the tach: "It's gonna blow up!" Yeah, it might, but it hasn't in the first 337k miles I've driven it...

Rick

Reply to
Rick Courtright

My '91 Jeep with 185HP (in 4W drive) smokes my '03 H6-3.0 from a standing start. My wife drives the subbie and she could care less about the acceleration though. She just wants it to be reliable and get her "there" without fuss nor muss in the winter and do it comfortably.

Al

Reply to
Al

It's a 2.2l, manual tranny. Tonyrama

Reply to
tonyrama

So, here's another wrinkle: Back when I bought my car, they replaced the gearbox with one from a '97 Outback (mine is a Legacy L). They told me that the gears would be little taller. I think I might be more happy with shorter ratios, but that's one of the things I'm trying to figure out. Tonyrama

Reply to
tonyrama

Well, anyone know where I can find this info for a Subaru 2.2L? Tonyrama

Reply to
tonyrama

Is there a way to improve throttle response?

Yeah, my Miata will rev all day right off the rev limiter, and beg for more. The Subaru, well, it feels useless to go past 4k RPMs. The oomf just isn't there.

Tonyrama

I have a buddy who drives big V-8's in his pickups who

Reply to
tonyrama

If the AWD is the problem, how does the WRX fit in? I've never driven one, but I've heard they are quite quick (and fast).

Tonyrama

Reply to
tonyrama

Outback probably has higher top speed and can accelerate better above 100 mph. I'd take torque over hp. Much more useful for day to day driving. I'm lucky when I have an opportunity to do 100+ mph once a week and then I won't be terribly upset if I could do only120 instead of 130 mph that would've been possible with sleeker but otherwise gutless at the low end car.

Anyway, is top speed on H6 electronically limited or it's drag limited?

Reply to
Apu Nahasapeemapetilon

My Subie's old, with the EA-82 engine, and there doesn't seem to be much that can be changed, but perhaps the newer ones allow "reprogramming" of the ECU? You know, the "performance chip" kinda stuff?

This may sound strange, but I've been told the ECU "learns" a lot about your driving habits, watching throttle opening, RPMs at shift points and all kinds of stuff, then "mixes" that new "knowledge" with whatever's programmed from the factory. With my engine, if I spend a couple of weeks driving around town without hitting the freeway, then try to wind it up pretty well, it falls off around 4k like you mentioned, but if I make it a point to take it out to 5k or better on a couple of onramps every couple of days, it stays "perkier." Maybe I'm imagining all this? But it "seems" real!

Rick

Reply to
Rick Courtright

Hi,

Gears can make or break the performance of a vehicle, especially if it's not loaded with wasted power capacity. I could give a couple of examples, but suffice it to say the "shorter" geared transmission will usually feel "quicker" than the "taller" geared one, but then there are issues of fuel economy, engine revs at speed, etc. that the engineers must take into account. In my experience, most cars and many trucks today are geared way too high for real life cuz they get better fuel economy in the dyno tests with taller gears. But this hurts them on the street, IMO!

Rick

Reply to
Rick Courtright

Well, I know for a fact top speed on my car is 92 MPH, and that was on a down grade Tonyrama

Reply to
tonyrama

Here's the best explanation I've ever run across: Click

formatting link
Borrowing from the page:

Horsepower = (Torque * RPM) divided by 5252

"Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at

4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same."
Reply to
Skweezieweezie

Or, how would you make one? Tonyrama

Reply to
tonyrama

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.