horsepower:torque relationship?
01-23-2007, 03:42 PM
#41
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Originally Posted by Old SStroker
Physically, not really, because it's the force resulting from TORQUE at the drive wheels that causes the vehicle to accelerate. See post #32 above.
Realistically, think of HP as the "rate at which torque is applied", so if you said:
H.P. = how fast you can apply torque, you'd be closer.
"Twisting" harder and faster gets 'er done!
Remember that it's not peak torque or peak HP that causes the vehicle to accelerate best, but the area under the curve(s) in the rpm range in which the engine is operating.
Realistically, think of HP as the "rate at which torque is applied", so if you said:
H.P. = how fast you can apply torque, you'd be closer.
"Twisting" harder and faster gets 'er done!
Remember that it's not peak torque or peak HP that causes the vehicle to accelerate best, but the area under the curve(s) in the rpm range in which the engine is operating.
Power is the rate at which this amount of work is done...
...lol... torque, work, energy all have the same units...
So, yes, power is the rate at which torque is applied to do work (ftlb/s).
And I agree, the area under the torque curve in the operating range...
Last edited by joecar; 01-23-2007 at 03:48 PM.
01-23-2007, 03:50 PM
#42
TECH Senior Member
Originally Posted by Stang's Bane
From looking at dyno graphs, the area in which the engine has the most torque the rate of HP increase is the greatest. Is this a correct statement?
01-23-2007, 04:23 PM
#43
01-23-2007, 04:37 PM
#44
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For our purposes let's keep it simple. Horsepower is a measure of work done and when it comes to getting the work done, like getting from point A to point B the quickest, I'll make all of my decisions based on how can I average the most HP and get it to the ground between points A and B. If I could only have a TQ curve or a HP curve displayed on a dyno sheet, I'll take the HP curve, all I need to know.
01-23-2007, 04:57 PM
#45
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Originally Posted by joecar
lol, I know that literature numbers are made up for marketing purposes, I never dynoed, so I'll never know. 
i think it would be close tho, ive seen stock 6 speed LS1's dyno 320hp, 330tq.
01-23-2007, 07:06 PM
#46
If you think torque at the wheels is the answer, consider this thought example...
My riding lawn mower engine makes 20 HP at 2100 rpm. This calculates to 50 lb-ft of torque. Now I'm going to put a 100:1 gear box between my lawn mower engine and the wheels. This will multiply the torque at the wheels to 5,000 lb-ft of torque. This is more torque than a stout C5 Corvette launching in 1st gear (400 hp with a 5000 rpm clutch dump) which would put 3736 lb-ft to the wheels. Does anyone think my lawn mower with 5000 lb-ft of torque to the wheels will beat the Corvette through the quarter mile with only 3736 lb-ft of torque to the wheels (and much less torque as it shifts up through the gears)?
The Corvette will run the quarter mile in about 12 seconds. With all its torque it will take the lawn mower 10 minutes to run the quarter mile... (assumes a 24" tire diameter running at engine speed divided by the 100:1 gear ratio).
The point is torque is easily manipulated with gearing where-as horsepower is essentially constant through the gearing... In the example above its 20hp vs 400hp, not 5000 tq vs 3736 tq... Horsepower is KING baby...
Shirl Dickey
My riding lawn mower engine makes 20 HP at 2100 rpm. This calculates to 50 lb-ft of torque. Now I'm going to put a 100:1 gear box between my lawn mower engine and the wheels. This will multiply the torque at the wheels to 5,000 lb-ft of torque. This is more torque than a stout C5 Corvette launching in 1st gear (400 hp with a 5000 rpm clutch dump) which would put 3736 lb-ft to the wheels. Does anyone think my lawn mower with 5000 lb-ft of torque to the wheels will beat the Corvette through the quarter mile with only 3736 lb-ft of torque to the wheels (and much less torque as it shifts up through the gears)?
The Corvette will run the quarter mile in about 12 seconds. With all its torque it will take the lawn mower 10 minutes to run the quarter mile... (assumes a 24" tire diameter running at engine speed divided by the 100:1 gear ratio).
The point is torque is easily manipulated with gearing where-as horsepower is essentially constant through the gearing... In the example above its 20hp vs 400hp, not 5000 tq vs 3736 tq... Horsepower is KING baby...
Shirl Dickey
01-23-2007, 09:01 PM
#48
Originally Posted by 3.4camaro
thats because they didnt rev as high as they do now. did all the muscle cars back in the day go to 7000 rpm? no sir, they would redline lower, so they couldnt get into high hp numbers, but still had monster tq numbers.
wrong! Look at a Honda S2000, it revs 9K, but doesn't make more HP than an LS1 that revs to lets say 6500. The reason for many of the old numbers (which they aren't old, alot of vehicles today make more torque than HP), is stroke combinations with bore size,. head chamber designs, camshaft profiles, and injection limitations. The motors of yesteryear did not have the technology and engineering that we have available today. HP numbers were still up over 400hp from the factory on some cars. The difference is not how high you can rev your engine. Alot of Old Pontiac (meaning original Pontiac engines, like the 400, 455 etc) Racer's make 800+hp under 5500rpm
01-23-2007, 10:12 PM
#51
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Perhap this helps
Torque within an engine is a measure of Twist upon the Crank.
This force (twist) is created by cylinder combustion, a putt.
The more Putts per time the more force(V4, V8, V12 etc) hence more torque.
The force from a Putt is from the displacement and MAF, AFR, timing, etc.
The efficiency of the Putts changes with rpm.
If efficiency didnt change then the torque would be constant, since the pistons are fixed to the crank it would get the same putt force reguarless of the rpm. this is why the torque can stay constant when the engine is most efficient.
Torque at RPM is Power. These definitions are equivelent so there should be no discussion about which is more important. Torque is telling you how much work can be done and Power is telling you how much work is being done, on the Dyno they happen to be equivelent.
At least, that's how I see it.
Torque within an engine is a measure of Twist upon the Crank.
This force (twist) is created by cylinder combustion, a putt.
The more Putts per time the more force(V4, V8, V12 etc) hence more torque.
The force from a Putt is from the displacement and MAF, AFR, timing, etc.
The efficiency of the Putts changes with rpm.
If efficiency didnt change then the torque would be constant, since the pistons are fixed to the crank it would get the same putt force reguarless of the rpm. this is why the torque can stay constant when the engine is most efficient.
Torque at RPM is Power. These definitions are equivelent so there should be no discussion about which is more important. Torque is telling you how much work can be done and Power is telling you how much work is being done, on the Dyno they happen to be equivelent.
At least, that's how I see it.
01-23-2007, 11:06 PM
#54
FormerVendor
Originally Posted by gametech
Dear God! The original question was very adequately explained by a knowledgeable person in the first response. How is this thread 3 pages long?
He was trying to get an understanding of what HP and Tq really are and now is probably even more confused!
01-24-2007, 09:00 AM
#56
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Originally Posted by 1FSTZ71
wrong! Look at a Honda S2000, it revs 9K, but doesn't make more HP than an LS1 that revs to lets say 6500. The reason for many of the old numbers (which they aren't old, alot of vehicles today make more torque than HP), is stroke combinations with bore size,. head chamber designs, camshaft profiles, and injection limitations. The motors of yesteryear did not have the technology and engineering that we have available today. HP numbers were still up over 400hp from the factory on some cars. The difference is not how high you can rev your engine. Alot of Old Pontiac (meaning original Pontiac engines, like the 400, 455 etc) Racer's make 800+hp under 5500rpm
01-24-2007, 11:20 AM
#57
Originally Posted by dynocar
Quote, "HP numbers were still up over 400hp from the factory?" Not compared to todays SAE net manufacturer's more accurate rating system. Possibly a few rare exceptions like the GM ZL1 427, but take the 427/435 found in the 67-69 Vette, apples to apples, today that would be rated at around 360 - 375 HP which was possibly about as good as it got as we look at other mass produced offering of that era. I have dynoed many muscle cars and believe me, it's a long dyno session when the owner starts seeing the real numbers and comparing them to yesteryears inflated rating systems. "800+hp under 5500rpm", naturally aspirated?
01-24-2007, 11:24 AM
#58
TECH Fanatic
Originally Posted by MrEracer
If you think torque at the wheels is the answer, consider this thought example...
My riding lawn mower engine makes 20 HP at 2100 rpm. This calculates to 50 lb-ft of torque. Now I'm going to put a 100:1 gear box between my lawn mower engine and the wheels. This will multiply the torque at the wheels to 5,000 lb-ft of torque. This is more torque than a stout C5 Corvette launching in 1st gear (400 hp with a 5000 rpm clutch dump) which would put 3736 lb-ft to the wheels. Does anyone think my lawn mower with 5000 lb-ft of torque to the wheels will beat the Corvette through the quarter mile with only 3736 lb-ft of torque to the wheels (and much less torque as it shifts up through the gears)?
The Corvette will run the quarter mile in about 12 seconds. With all its torque it will take the lawn mower 10 minutes to run the quarter mile... (assumes a 24" tire diameter running at engine speed divided by the 100:1 gear ratio).
The point is torque is easily manipulated with gearing where-as horsepower is essentially constant through the gearing... In the example above its 20hp vs 400hp, not 5000 tq vs 3736 tq... Horsepower is KING baby...
Shirl Dickey
My riding lawn mower engine makes 20 HP at 2100 rpm. This calculates to 50 lb-ft of torque. Now I'm going to put a 100:1 gear box between my lawn mower engine and the wheels. This will multiply the torque at the wheels to 5,000 lb-ft of torque. This is more torque than a stout C5 Corvette launching in 1st gear (400 hp with a 5000 rpm clutch dump) which would put 3736 lb-ft to the wheels. Does anyone think my lawn mower with 5000 lb-ft of torque to the wheels will beat the Corvette through the quarter mile with only 3736 lb-ft of torque to the wheels (and much less torque as it shifts up through the gears)?
The Corvette will run the quarter mile in about 12 seconds. With all its torque it will take the lawn mower 10 minutes to run the quarter mile... (assumes a 24" tire diameter running at engine speed divided by the 100:1 gear ratio).
The point is torque is easily manipulated with gearing where-as horsepower is essentially constant through the gearing... In the example above its 20hp vs 400hp, not 5000 tq vs 3736 tq... Horsepower is KING baby...
Shirl Dickey
I liked your thought experiment as far as it went which was 1.5 mph.
It might be argued that given enough a 1.0g launch, your 100:1 mower might just beat the Vette to 1.5 mph (mower's top speed @ 2100 engine revs/min). Of course at 1.0 g it will be at 1.5 mph in less than 2 inches and in less than .07 seconds, so timing might be a problem. It gives new meaning to "short time".
Here's another thought experiment:
Current F1 engines make about 750 hp @ 18,000 rpm. 750 hp @ 9,000 rpm would be pretty easy for a Nextel Cup engine. Lets assume the same diameter rear tires on both cars (which isn't all that far off).
Gear both cars to reach 180 mph @ engine power peak (18,000 and 9,000).
To make it an easier thought experiment, assume the same amount of frictional losses in the drivelines. Again not too far off even though the F1 engine is spinning 2X as fast.
1) How does the torque at the flywheel compare for the F1 engine and the Cup engine @ the power peak rpms?
2) How does the torque at the drive wheels compare for the F1 car and the Cup car @ the power peak rpms (180 mph in this example)?
3) How does the horsepower at the flywheel and the rear wheels compare?
The F1 car weighs less that 40% of the Cup car, but has a lot more drag @ 180 so if would be difficult to compare the resulting vehicle acceleration @ 180.
One further thought: if the F1 engine and the Cup engine had similarly shaped torque curves (which isn't all that far off), and you put the F1 engine in the Cup car with appropriate gearing, would the rear tires know the difference in what engine provided the torque?
Keep on thinkin'! It keeps us young.
01-24-2007, 01:13 PM
#59
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Originally Posted by Ed Wright
How true. Older 454" Vette guys don't like seeing around 300 hp.
01-24-2007, 01:43 PM
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Originally Posted by MrEracer
Quote:
I hope your lawn mower has at least a 20,000 RPM rev limit with that gear! ; )
Even with a 20,000 rpm rev limit, assuming a flat torque curve, the lawn mower will still only have 191 hp. The Corvette still wins...
Shirl
I hope your lawn mower has at least a 20,000 RPM rev limit with that gear! ; )
Even with a 20,000 rpm rev limit, assuming a flat torque curve, the lawn mower will still only have 191 hp. The Corvette still wins...
Shirl
Ever feel like they were ready to shoot the messenger, Ed? Had a guy that had, a '63' small block Vette rated at 340 HP, did that 327's typical, barely 200 RWHP routine again, he was mad. If everyone thinks that explaining the relationship between HP and TQ is difficult, how would you like trying to explain this to the rose glassed muscle car crowd?
Last edited by Wnts2Go10O; 01-24-2007 at 01:48 PM.