engineermike

The one that I like to bring up in hp vs torque discussions, that always twists some brains into noodles is...

The M1 Abrams tank produces 1,500 hp and . . . wait for it. . . 395 ft-lb of torque at peak.

I, with a 10 ft cheater bar, can produce 4,000 ft-lb. I can produce much more with a longer bar. Archimedes said, "Give me a long enough lever, and I can move the world."

Torque can be manipulated using gears and levers, whereas hp can not. And, yes, you can manipulate hp by "simply" raising engine speeds, but this requires things like long duration camshafts, high flow cylinder heads, headers, etc... which are proven to also make the cars faster, not by coincidence.

Think about the fact that you are forced to upshift to higher gears that have less mechanical advantage (i.e. 1:1 vs 3.06:1). If you manage to make 400 ft-lb of torque, but modify your engine in such a way that you can maintain 400 ft-lb at twice the rpm, then you could hold each gear twice as long. Imagine how much faster your car would be if you could shift out of 1st gear at 70 mph instead of 35 while maintaining the same ratios. Well...the result of keeping the same torque at double the engine speed is double the hp.

1989 305 TBI made 223 ft-lb at 4000 rpm (170 hp)
If you can make 223 ft-lb at 8000 rpm, you get 340 hp
If you manage to make 223 ft-lb at 12000 rpm, you get 510 hp
Try spinning a 305 TBI to 12000 rpm!

Mike

Silver2000WS-6

iTrader: (1)

Thanks for the input guys, but I found the information I was looking for. I think there was a little confusion in how I asked the question, sorry about that. In other words I am not as confused as you may think lol I just did not do a good job expressing my question.

Silver2000WS-6

iTrader: (1)

Yes you can like I said earlier
Tractive Force=(Torque*Gear Ratios*Efficiencies)/Tire Radius
Then I would say
Acceleration=(Tractive Force-Drag Force-Rolling Resistance Force)/Mass

I can did up an Excel spread sheet that we did on a stock car if you would like to see it. It was actually pretty accurate, within 0.1s in a 1/4 according to Car and Driver. However we did account for drag and rolling resistance. I think it was a Jetta not a real cool car but that what the teacher wanted us to do.

racer7088

No you can't.

One car has an engine that makes 400 ft pounds of tq and weighs 3000 pounds.

One car has an engine that makes 500 ft pounds of tq and weighs 3000 pounds.

Which is faster?

You can't tell only knowing what tq they put out.

Silver2000WS-6

iTrader: (1)

Haha no I mean like using 50 different data points. I looked and I don't have that Excel spreadsheet, but I will see if my teacher still has it. If so I will post it up for you to look at, it is pretty cool. Actually all the engine data we had was redline, max torque @ a certain speed, and max power @ a certain speed. From there we plug them into some crazy equation and solved for coefficeints then made a simulated torque curve. I know that torque curve wasn't perfect, but suprisingly it got the job done.

racer7088

If you have Tq at a certain speed it is HP which again can tell you something.

Tq alone has no impact on performance unless it is referenced at a linear or angular speed which again makes it horsepower.

If you need any RPM data then the spreddsheet you are looking at used HP to find acceleration.

joecar

Go back to basics...

assuming T is constant:

W = T.Θ

P = dW/dt = d(T.Θ)/dt = Θ.dT/dt + T.dΘ/dt = T.ω

P expresses the time rate of work done... i.e. the rate of torque producing angular movement...
it "summarizes" T and ω... it is a handy "tool".

Compare 100 lbft at 100 rev/s and at 200 rev/s.

Edit: found a better symbol for angular displacement.

Silver2000WS-6

iTrader: (1)

Thank you but I know what power and torque are. That spreadsheet I used DID NOT use power to calculate acceleration. I only used engine speed to reference the particular torque data for that instant and to calculate the vehicle's velocity. I know I easily could have taken power data and divided out the engine speed to get it in term of torque, but I am just saying you do not need to actually figure a power #s to calculate acceleration.

,Chase

racer7088

If you are referecing torque at a rotational speed you are talking HP. You don't seem to understand that. Acceleration involves and is in reference to time and so you need rpm to se how much work you can do in a certain time. This is a HP scenario plain and simple. That's why in Physics you learn about power because it is what gets work done at the rate you are looking for. We care about the time involved!

If you can do 20 revolutions of a crank at 50 foot pounds of work in a minute and I did 40 revolutions of a the same crank at 50 foot pounds of work in a minute then I could do twice the work you did in a minute and I would also be producing twice the power as you did. I could use a different gear twice as low and create twice the tq at the wheels at the same wheel speed as you could since I make double the power even though we were both supplying the same input torque.

Torque on it's own doesn't mean anything at all!

engineermike

Yes, but the torque applied to the rear wheels decreases as speed increases, no? If the torque stayed the same as speed increased, hp would be infinite.

Silver2000WS-6

iTrader: (1)

No I actually used a torque curve for the calculation, so the torque was not constant.

engineermike

Did you factor in that the gear ratio is progressively taller as you increase speed and shift to higher gears?

Silver2000WS-6

iTrader: (1)

Yeah bud it is a pretty awesome spreadsheet. We even accounted for drag and rolling resistance with respect to the cars velocity.

DanO

this thread is kinda pointless...

you claim all this stuff you do in your upper level engineering course... yet dont understand power? Accounting for drag and rolling resistance in a spreadsheet your professor put together is hardly impressive. We have tried to assist in your learing yet it doesnt seem to work

Power = torque x rpm ... you used power in your professors spreadsheet

did you use torque? yes

did you use rpm? yes

Does that mean power? yes!!

engineermike

Ok well if it includes the fact that the gear ratio is steeper as speed increases, thereby reducing torque delivered to the tires, then it automatically includes hp.

Silver2000WS-6

iTrader: (1)

This thread is pointless. I said from the beginning that P=Tw, but I never did that in my spread sheet. I am not the one being hard headed hear I am just saying that I never multiplied my engine torque by my engine speed.

Sharpe

iTrader: (7)

Is there a chaper on "Bullshitting About Moot Points" in the book? Take it to a general forum. This is not Advanced Engineering by a long shot.

landonew

You didn't have to. You held RPM constant so torque was representative fo HP


Simple math.

P=T*2(pi)*rpm

If RPM is held constant, then 2(pi)*rpm is just a multiplier

How can you not understand that?


I am an electrical engineer and I remember be confused over this back in school before understanding rotational kinetics. You don't fully understand that torque is a rotational force on a shaft. This is different than linear force applied to an object.