Why do people get so caught up in horsepower?
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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
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
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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.
Last edited by Silver2000WS-6; Apr 19, 2009 at 01:22 PM.
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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.
Last edited by Silver2000WS-6; Apr 19, 2009 at 01:30 PM.
FormerVendor
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From: Houston, Tx.
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.
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.
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.
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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.
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From: Houston, Tx.
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.
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.
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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.
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.
Last edited by joecar; Apr 24, 2009 at 08:20 AM. Reason: Found a symbol Θ for angular displacement
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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.
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.
,Chase
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Brett Foote FormerVendor
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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
,Chase
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!
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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
,Chase
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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!!
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!!
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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.
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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
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
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.
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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.
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