OT, but I like the intercooler exhaust, and the aero wiper cover panel...

 

wow, folks we kind of beat that one to death.

torque is just a part of HP. it is a common misconception that torque is what you should focus on (ie engine torque. ) as was pointed out, i guess that 18,000rpm 250ftlb F1 engine isnt really that fast!! ha ha. 1000hp is 10000hp and thats what does the work, from a broader perspective. You can take the hp and caculate the actual torque through the gearing, but make no mistake, its the HP that does the work. work = force x displacement . HP is a rate of doing work. engine torque is just part of the equation. torque is as usless to talk about alone as RPMs are. put them both together and you have SOMETHING to talk about.

I always use the example of a two 500hp cars , one with 500ftlbs of torque and the other at 250ftlbs of torque. which one is faster around a track or in a drag? they theoretically should be identical, providing the shape of the curves are equal and the gearing differences are proportionally diffferent.

where the shape of the hp curve comes into play is in driveability, meaining, dont want to downshift, even thought that would buy you greater acceleration rates. However, in racing, you rarely ever find a car running near its peak engine torque anyway. aways operating at the max HP areas under the HP curves. thats why redline is the shift point. (not near max torque)

Mk

 

Craziest numbers I've seen in a while - Last weekend at an SCCA AX - guy starts up a very stock looking newer VW BEetle - I could hear it was a diesel. I kinda laughed to myself..."This should be funny..."
Imagine my surprise when the guy just SCREAMED around the course.

Turns out: Turbo diesel with 30 (THIRTY!) lbs of boost. Dynoed @ 245hp and 440 ft/lbs torque!

 

Yes, thats it.

It's HP that you really are looking at for both acceleration and top speed. (the hp only is top speed analogy is incorrect) Hp incorporates the other equally important factor, speed (rate of doing work), rpms, etc.

if you have a torque number, its meaningless unless you tie a rpm to it. with the rpm, you cand find a gear that gets the highest torque for acceleration, which will be in the highest HP range, not the highest engine torque range.

Glen is right too!

MK

 

I think the attempts to explain HP and Torque are tainted with contradictions (to me at least).

I personally go back to the basic definitions from physics class:
Power is a function of WORK (Force x distance) over TIME
Torque is a function of FORCE at a discrete interval in time

I also think we keep forgetting that the numbers for engine specs are "peak" values only
To me, it makes sense...I think!!

Clear as mud?

 

A steam train makes huge torque even at 0 RPM, because the steam is pushing the piston. So you will sometimes see the drive wheels spin and grab as the engine tries to move all those cars. With a 1 cylinder engine at 100 rpm you have 50 power strokes on a 4 stroke engine or 100 on a two stroke. This is why 2 stroke motorcycles are more powerful than 4 stroke engines of the same displacement because they are doing twice the work at a given RPM. An 8 cylinder 4 cycle engine at 100 RPM is going to have 400 power strokes . The one cylinder would have to be going 400 rpm to match it, given equal cylinder displacement. You can see why 4 and 6 cylinder engines would tend to need to rev to make power, and the 8 would have more twist at lower rpm and not need to be as radical in the compresion, camshaft departments. An 80 928 is a very mild engine that runs out of cam as revs rise but still makes good low down power. Cams have the function of letting air and fuel into the engine and need greater duration for high RPMs because there is less and less time to let air into the engine the faster it goes. Turbo-Supercharging forces more air and fuel into an engine, making it act as if it has more displacement because it is proccessing more air and fuel in each cylinder. Turbos tend to make more power at high RPMs because there is more exhaust driving the turbo. The effect builds. Superchrgers lose power at a certain point because they spin at a speed directly with the engine and do not build proportionately. They run into the time vs. filling issue with no additional pressure to offset it. Hope this helps.

 

If I take my torque wrench and apply 100 ft-lbs to a bolt, my horsepower is still 0 because nothing's moving. If I could spin the wrench around once-per-second at 100 ft-lbs of torque (in theory the bolt does not snap off) , I would generate 100/5250 = 0.02 horsepower. If I could spin the wrench 5250 times per second, I would be generating 100 hp.

Speaking of diesel engines, take a look at this web site:

http://www.bath.ac.uk/~ccsshb/12cyl/

 

Most car engine specs (in English units) have a peak hp/peak torque ratio of about 1.0.

Notice that the diesel ship engine specs state 5.6 million ft-lbs torque max, but "only" 108,000 hp. The ratio of peak hp/peak torque is only 0.02. The reason is that this ship engine only revs up to 100 rpm. If this engine could run at 5250 rpm and maintain the same torque, in theory it would generate 5 .6million hp.

So I think what Mark Kibort is saying, torque and horsepower are not two different "things". The engine produces only one thing, horsepower. Torque, by itself, is not a function of time. When people say an engine has a lot of low-end torque, they really mean it has a lot of low-end horsepower.

 

I wonder if Renegade makes a conversion kit for that one??

 

Surprisingly it's power-to-weight ratio of 42lbs/hp is not all that bad (probably close to your average minivan). Or course that's not counting the weight of the 928 you put it in.

 

Well said. sometimes we need a slightly different explaination approach.

mk

 

Hey, you can measure both Torque and Hp this weekend at DEVEK

 

Thanks to everyone for demystifying this for me. What I think I know:

Torque is the force that turns the crankshaft. Horsepower is the amount of work (or power, if you prefer) that the engine is generating. Since the engine does no work unless the crankshaft spins, horsepower is zero regardless of how much torque is applied at 0 RPM. From this, it is intuitive that an engine's horsepower number is only meaningful when associated with a specific RPM. It is also intuitive that horsepower is the more important number. Where torque numbers are important are where in the RPM band most of the torque is occurring. Furthermore, now that I know what torque is, it is now clear to me why large-displacement engines are capable of generating so much of it, and why smaller displacement engines need to be built for higher revs in order to be quick, particularly on the racetrack.

Did I get it?

 

Kind of.

actually, think of HP having most of the information for you , or doing most of the work for you. If you only have torque, then, you need to multiply speed or RPMs into the equation to find what you are looking for. SINCE, torque is a part of HP, HP incorporates the speed factor, so you dont have to. by using area under the HP curve, it doesnt matter whether you have a 500ftlb torque engine or a 200ftlb engine. its all about the HP to the driven wheels that counts.
you look at gear spacing, and peak rpms and then you can determine what the car is putting down at the wheels. (without having to multipy torque ,x rpms, through the gear box , at a particular speed based on those gear ratios).

as far as torque with no movement, that would be called a 0 net torque. there would be offsetting torques. (you applying 200ftlbs on a wrench and the stuck bolt app resisting the same amount for an example . on the force side, you sitting in a chair, 180lbs of force downward due to gravity, but no movement, as the chair is pushing back with the same force. this also would be 0 net force. a positive net force, or torque, will result in movement and then you can calculate the rest.


MK

 

911Dave,

You got it well enough.

Mark,

It's all about force at the road. The instantaneous element is force.

A body (rod, chair whatever) subjected to balanced forces still experiences force. The result is no "net motion." It's like the difference between stress and strain.