I need your help- HP vs torque discussion
02-15-2009, 11:16 PM
#31
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Thread Starter
more average HP or HP-seconds the faster it will be over any speed range.
Of course the rate of acceleration in each gear is fastest at the highest torque in that gear but comparitive to another vehicle at the same speed it will be easier to compare HP at those speeds. after all in most race conditions you will probably never even see peak torque as most operation is a tad over peak torque rpm .
no argument that a boader HP curve is better and that is usually dictated by a higher torque value if the redline is the same for both cars. if it isnt closer examination of the HP curves is required. Its not the rule though and that was the point of the entire thread on the racing board.
Mk
Of course the rate of acceleration in each gear is fastest at the highest torque in that gear but comparitive to another vehicle at the same speed it will be easier to compare HP at those speeds. after all in most race conditions you will probably never even see peak torque as most operation is a tad over peak torque rpm .
no argument that a boader HP curve is better and that is usually dictated by a higher torque value if the redline is the same for both cars. if it isnt closer examination of the HP curves is required. Its not the rule though and that was the point of the entire thread on the racing board.
Mk
I've owned, driven, and raced a 89 944 Turbo S, 01 BoxsterS. The max speed for 1st thru 3rd the same and same rev limit. The cars weigh the same. 0-60 specs are the same on both cars. Same rated top speed 168mph. The torque curve on the Turbo was much different than the boxster. The boxster's torque curve peaked much lower and fell off were the turbo had almost no torque or hp until above 3000 rpm then remained almost flat to red line. The boxster felt much slower 0-60 and ran out of umph much above 60. 60-100 the turbo would run off and leave the boxster. These two cars have the same peak hp.
I've also owned and raced a 90 928 GT with guess what...the same 0-60 and 1st thru 3rd max mph/rpm as the other two cars. The 928 was heavier but had more hp and torque. The torque curve was the flattest of the three and it also felt the slowest. 60-100 the 944 Turbo was still faster, above 120 (4th gear) the 928 would run off and leave the other two cars.
To tell the difference in the way these cars perform with the hp curve would be very difficult where the torque curve is much easier. Why is that if hp so accurately represents the rate of acceleration? The rate of acceleration difference I felt driving the cars was obviously following their torque curves.
The differences in what we think makes things fast is why there is racing.
I've also owned and raced a 90 928 GT with guess what...the same 0-60 and 1st thru 3rd max mph/rpm as the other two cars. The 928 was heavier but had more hp and torque. The torque curve was the flattest of the three and it also felt the slowest. 60-100 the 944 Turbo was still faster, above 120 (4th gear) the 928 would run off and leave the other two cars.
To tell the difference in the way these cars perform with the hp curve would be very difficult where the torque curve is much easier. Why is that if hp so accurately represents the rate of acceleration? The rate of acceleration difference I felt driving the cars was obviously following their torque curves.
The differences in what we think makes things fast is why there is racing.
02-16-2009, 12:09 AM
#32
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hey Mark---
your first answer---it depends......
in my kind of racing, we don't depend on HP or torque per se, because each type of engine makes the driving experience different.
small blocks typically have to be revved higher to make the same performance as the big blocks. and even then, the higher rev's aren't the cure-all for equaling out the performance (torque) disadvantage of the small blocks.
that may be the answer you are looking for.......(?)
--Russ
your first answer---it depends......
in my kind of racing, we don't depend on HP or torque per se, because each type of engine makes the driving experience different.
small blocks typically have to be revved higher to make the same performance as the big blocks. and even then, the higher rev's aren't the cure-all for equaling out the performance (torque) disadvantage of the small blocks.
that may be the answer you are looking for.......(?)
--Russ
02-16-2009, 01:22 AM
#33
Rennlist Member
I am just having a hard time with why you feel hp is the end all be all when both curves are providing a view of the same data. Is it because a hp curve makes higher rpm look faster?
02-16-2009, 04:23 AM
#34
Rennlist Member
Thread Starter
Did you look at the two sets of curves. both have near simular HP curves but the torque curves are totally different. (shifted by RPM) .
I can use a calculator as well as anyone and the torque curve is as useful as it is a factor of the HP curve which only has double the information. (torque and rpm). So its not that HP is the end all catch all. in fact you need time to really see what has been done. remember HP is the rate of doing work. HP seconds are a unit measure of work like a Kilowatt-hour would be at your home. Obviously the faster you accelerate the more energy you will use.
As someone said in the previous threads, you dont see the sanctioning bodies of racing using torque to HP ratios!
so by looking at HP you dont need to look at the multiplied torque through the gear ratios acting on the tires. comparing two cars is as simple as comparing their HP curves at any and all speeds.
Mk
I can use a calculator as well as anyone and the torque curve is as useful as it is a factor of the HP curve which only has double the information. (torque and rpm). So its not that HP is the end all catch all. in fact you need time to really see what has been done. remember HP is the rate of doing work. HP seconds are a unit measure of work like a Kilowatt-hour would be at your home. Obviously the faster you accelerate the more energy you will use.
As someone said in the previous threads, you dont see the sanctioning bodies of racing using torque to HP ratios!
so by looking at HP you dont need to look at the multiplied torque through the gear ratios acting on the tires. comparing two cars is as simple as comparing their HP curves at any and all speeds.
Mk
02-16-2009, 04:30 AM
#35
Rennlist Member
Thread Starter
Thats the common and usually right answer. however the performance of the larger blocks is due to more HP not just torque. the small blocks just cant produce the power even at the higher rpm. It boils down to power in the end.
after all, if you are going to accelerate a mass it takes power to do it and that rate will be proportional to the power.
Acceleration=Power/(mass x velocity)
what kind of racing is not dependent on a mix of rpm and torque (i.e. HP)?
mk
after all, if you are going to accelerate a mass it takes power to do it and that rate will be proportional to the power.
Acceleration=Power/(mass x velocity)
what kind of racing is not dependent on a mix of rpm and torque (i.e. HP)?
mk
hey Mark---
your first answer---it depends......
in my kind of racing, we don't depend on HP or torque per se, because each type of engine makes the driving experience different.
small blocks typically have to be revved higher to make the same performance as the big blocks. and even then, the higher rev's aren't the cure-all for equaling out the performance (torque) disadvantage of the small blocks.
that may be the answer you are looking for.......(?)
--Russ
your first answer---it depends......
in my kind of racing, we don't depend on HP or torque per se, because each type of engine makes the driving experience different.
small blocks typically have to be revved higher to make the same performance as the big blocks. and even then, the higher rev's aren't the cure-all for equaling out the performance (torque) disadvantage of the small blocks.
that may be the answer you are looking for.......(?)
--Russ
02-16-2009, 02:45 PM
#36
Chronic Tool Dropper
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Mark,
I really have to bite my tongue when I read your explanations. I'm sure there's a thread of reason buried in there somewhere. It just needs better explaining.
Lots of closet fizzycists have a usable understanding of the subject, yet can't teach it successfully.
I really have to bite my tongue when I read your explanations. I'm sure there's a thread of reason buried in there somewhere. It just needs better explaining.
Lots of closet fizzycists have a usable understanding of the subject, yet can't teach it successfully.
02-16-2009, 03:19 PM
#37
Race Car
Exactly what Dr. Bob said. The direct answer to RKD's question as to why the HP curve is a better gauge of performance, is that you don't need to know the gearing of the cars being compared. If you only look at the torque curves, you also need to know gear ratios.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
02-17-2009, 04:14 AM
#38
Rennlist Member
Thread Starter
If you caught it mid stream, you might have caught the explanations after there was some resistance to the straight forward reasoning.
I like boiling it down to simple levels. I thought that is what I had done, but remember it went on for mega pages. The first comment on this thread was a description of the discussion. What was not clear enough there?
The bottomline, is that I was trying to show that its power that determines rates of acceleration, and better said, average hp (call it area under the curve) or HP-seconds which is time spent in the varied HP range. Engine torque and engine torque curves are very difficult to understand, especially if you are not able to apply all the gear ratios to them. Hp does take a few steps out of the analysis. Just compare the HP curves, regardless of engine torque values or shapes of curves and you can compare most any engine very easily.
Is there any issue with this logic or explanation? Just curious to see where my point might have been missed, or been lost.
As you might imagine, on a white board, in person, this kind of discussion is over in a few minutes, even with any type of misinformed fizzisist.
mk
I like boiling it down to simple levels. I thought that is what I had done, but remember it went on for mega pages. The first comment on this thread was a description of the discussion. What was not clear enough there?
The bottomline, is that I was trying to show that its power that determines rates of acceleration, and better said, average hp (call it area under the curve) or HP-seconds which is time spent in the varied HP range. Engine torque and engine torque curves are very difficult to understand, especially if you are not able to apply all the gear ratios to them. Hp does take a few steps out of the analysis. Just compare the HP curves, regardless of engine torque values or shapes of curves and you can compare most any engine very easily.
Is there any issue with this logic or explanation? Just curious to see where my point might have been missed, or been lost.
As you might imagine, on a white board, in person, this kind of discussion is over in a few minutes, even with any type of misinformed fizzisist
.mk
02-17-2009, 07:37 AM
#39
Three Wheelin'
Mark, how comes a electric car outruns easy a internal combustion one , with alot less HP , but alot more torque ????????????? 
seen yesterday in Top Gear , a Lotus against a electric one.....
seen yesterday in Top Gear , a Lotus against a electric one.....
02-17-2009, 01:40 PM
#40
Rennlist Member
Thread Starter
my second favorite example, (first one is the jet vs the car or motorcycle)
The reason......... POWER!
If you look at the comparisons, they usually always compare the car against something heavier or with less HP to weight. its quite simple. the electic car (The tesla) has almost 300hp in reality. It weighs a little over 2500lbs. It has only one gear.(equivilant to our first gear at about 8.5:1 total reduction. So, if it was in our car, picture you running your car to 55mph in only first gear, then leaving it in 1st gear for the rest of the quarter mile. (say 110 mph). the electric car goes to over 14,000rpm!
we have to dump the clutch at 3000rpm, the electric car just pushes the power level switch. say you have an equal launch. at that point, both cars with the same HP would have the same torque to the wheels . however, the electric car with its torque falling after 80mph, starts to run into some real bad HP fall off. with a 2 speed gear box that could be fixed, but without it, 80-120mph is not very impressive.
Im sure for a drag racer, eliminating clutch slip and only worrying about tire slip would be a huge advantage. (maybe not so much for someone very skilled at it)
Here is the torque /power curves. notice HP is in KWs. notice how they compare the curves to a gas engine with much less HP.
in the end, its all HP/weight, and again, the amount of hp you can apply with gas or electricity, at any vehicle speed that determines the acceleration at that speed.
So, to directly answer your question, those electric vehicles have been much ligher and much more powerful compared to the competitors weight. If they were equal weight and had the same power, the gas engine vehicle would win the race due to the reduced effectiveness of the electric car's fixed gear ratio at speeds above 80mph.
adjust the curves below for top rpm and actually a gas engine car would be pretty similar in "Shape". remember, its the shape of the HP curve that matters as well.
aside from the instant torque from standstill, which is more convenient than anything else, the curves are not too different than a gas engine, IF you used two that were at least rated at the same HP! (power level). Marketing! Sheeez.
Lotus s1dyno plot:
http://www.dyno-plot.co.uk/dyno/dyno...Eliseparts.htm
mk
by the way, 200Kw power is about equal to 265HP. Notice the curve below shows the performance compared to a 120hp lotus engine.
I would love to race one of these at the track. I think it would be really cool!!
The reason......... POWER!
If you look at the comparisons, they usually always compare the car against something heavier or with less HP to weight. its quite simple. the electic car (The tesla) has almost 300hp in reality. It weighs a little over 2500lbs. It has only one gear.(equivilant to our first gear at about 8.5:1 total reduction. So, if it was in our car, picture you running your car to 55mph in only first gear, then leaving it in 1st gear for the rest of the quarter mile. (say 110 mph). the electric car goes to over 14,000rpm!
we have to dump the clutch at 3000rpm, the electric car just pushes the power level switch. say you have an equal launch. at that point, both cars with the same HP would have the same torque to the wheels . however, the electric car with its torque falling after 80mph, starts to run into some real bad HP fall off. with a 2 speed gear box that could be fixed, but without it, 80-120mph is not very impressive.
Im sure for a drag racer, eliminating clutch slip and only worrying about tire slip would be a huge advantage. (maybe not so much for someone very skilled at it)
Here is the torque /power curves. notice HP is in KWs. notice how they compare the curves to a gas engine with much less HP.
in the end, its all HP/weight, and again, the amount of hp you can apply with gas or electricity, at any vehicle speed that determines the acceleration at that speed.
So, to directly answer your question, those electric vehicles have been much ligher and much more powerful compared to the competitors weight. If they were equal weight and had the same power, the gas engine vehicle would win the race due to the reduced effectiveness of the electric car's fixed gear ratio at speeds above 80mph.
adjust the curves below for top rpm and actually a gas engine car would be pretty similar in "Shape". remember, its the shape of the HP curve that matters as well.
aside from the instant torque from standstill, which is more convenient than anything else, the curves are not too different than a gas engine, IF you used two that were at least rated at the same HP! (power level). Marketing! Sheeez.
Lotus s1dyno plot:
http://www.dyno-plot.co.uk/dyno/dyno...Eliseparts.htm
mk
by the way, 200Kw power is about equal to 265HP. Notice the curve below shows the performance compared to a 120hp lotus engine.
I would love to race one of these at the track. I think it would be really cool!!
Last edited by mark kibort; 02-17-2009 at 02:18 PM.
02-17-2009, 02:33 PM
#41
Three Wheelin'
my second favorite example, (first one is the jet vs the car or motorcycle)
The reason......... POWER!
If you look at the comparisons, they usually always compare the car against something heavier or with less HP to weight. its quite simple. the electic car (The tesla) has almost 300hp in reality. It weighs a little over 2500lbs. It has only one gear.(equivilant to our first gear at about 8.5:1 total reduction. So, if it was in our car, picture you running your car to 55mph in only first gear, then leaving it in 1st gear for the rest of the quarter mile. (say 110 mph). the electric car goes to over 14,000rpm!
we have to dump the clutch at 3000rpm, the electric car just pushes the power level switch. say you have an equal launch. at that point, both cars with the same HP would have the same torque to the wheels . however, the electric car with its torque falling after 80mph, starts to run into some real bad HP fall off. with a 2 speed gear box that could be fixed, but without it, 80-120mph is not very impressive.
Im sure for a drag racer, eliminating clutch slip and only worrying about tire slip would be a huge advantage. (maybe not so much for someone very skilled at it)
Here is the torque /power curves. notice HP is in KWs. notice how they compare the curves to a gas engine with much less HP.
in the end, its all HP/weight, and again, the amount of hp you can apply with gas or electricity, at any vehicle speed that determines the acceleration at that speed.
So, to directly answer your question, those electric vehicles have been much ligher and much more powerful compared to the competitors weight. If they were equal weight and had the same power, the gas engine vehicle would win the race due to the reduced effectiveness of the electric car's fixed gear ratio at speeds above 80mph.
adjust the curves below for top rpm and actually a gas engine car would be pretty similar in "Shape". remember, its the shape of the HP curve that matters as well.
aside from the instant torque from standstill, which is more convenient than anything else, the curves are not too different than a gas engine, IF you used two that were at least rated at the same HP! (power level). Marketing! Sheeez.
Lotus s1dyno plot:
http://www.dyno-plot.co.uk/dyno/dyno...Eliseparts.htm
mk
by the way, 200Kw power is about equal to 265HP. Notice the curve below shows the performance compared to a 120hp lotus engine.
I would love to race one of these at the track. I think it would be really cool!!
The reason......... POWER!
If you look at the comparisons, they usually always compare the car against something heavier or with less HP to weight. its quite simple. the electic car (The tesla) has almost 300hp in reality. It weighs a little over 2500lbs. It has only one gear.(equivilant to our first gear at about 8.5:1 total reduction. So, if it was in our car, picture you running your car to 55mph in only first gear, then leaving it in 1st gear for the rest of the quarter mile. (say 110 mph). the electric car goes to over 14,000rpm!
we have to dump the clutch at 3000rpm, the electric car just pushes the power level switch. say you have an equal launch. at that point, both cars with the same HP would have the same torque to the wheels . however, the electric car with its torque falling after 80mph, starts to run into some real bad HP fall off. with a 2 speed gear box that could be fixed, but without it, 80-120mph is not very impressive.
Im sure for a drag racer, eliminating clutch slip and only worrying about tire slip would be a huge advantage. (maybe not so much for someone very skilled at it)
Here is the torque /power curves. notice HP is in KWs. notice how they compare the curves to a gas engine with much less HP.
in the end, its all HP/weight, and again, the amount of hp you can apply with gas or electricity, at any vehicle speed that determines the acceleration at that speed.
So, to directly answer your question, those electric vehicles have been much ligher and much more powerful compared to the competitors weight. If they were equal weight and had the same power, the gas engine vehicle would win the race due to the reduced effectiveness of the electric car's fixed gear ratio at speeds above 80mph.
adjust the curves below for top rpm and actually a gas engine car would be pretty similar in "Shape". remember, its the shape of the HP curve that matters as well.
aside from the instant torque from standstill, which is more convenient than anything else, the curves are not too different than a gas engine, IF you used two that were at least rated at the same HP! (power level). Marketing! Sheeez.
Lotus s1dyno plot:
http://www.dyno-plot.co.uk/dyno/dyno...Eliseparts.htm
mk
by the way, 200Kw power is about equal to 265HP. Notice the curve below shows the performance compared to a 120hp lotus engine.
I would love to race one of these at the track. I think it would be really cool!!
ok, Mark, you are a fighting rabbit !
... but there must be a formula which connects HP and torque to weight... no ? I think top speed will be function of HP , but how fast you get topspeed depends torque ... is there a formula ?
02-17-2009, 03:12 PM
#42
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The way to get most folks to see the light is to allow them 1000 ft-lbs of torque.... in the form of a _windmill_ turning 5 rpm, and put it up against a Honda Civic with 100 ft-lbs (at 5000 rpm)
02-17-2009, 03:24 PM
#43
Race Car
Dan
'91 928GT S/C
475hp/460lb.ft
02-17-2009, 03:37 PM
#44
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The windmill example forces the torque-oriented crowd to exaine what kind of gearing would be needed to make _use_ of the 1000 ft-lbs, at which point they're now on board.
And unlike 100,000 rpm motors, most folks have a gut feel for what a huge slow turning windmill is like.
It helps cause the "torque isn't very meaningful unless you know what rpm it's at" light to go on.
And unlike 100,000 rpm motors, most folks have a gut feel for what a huge slow turning windmill is like.
It helps cause the "torque isn't very meaningful unless you know what rpm it's at" light to go on.
02-17-2009, 05:37 PM
#45
Rennlist Member
Thread Starter
HP and torque are not connected. (torque at the rear wheels that is) . without RPM attached to torque, engine torque is absolutely meaningless. I can generate 350ft-lbs of torque on my rear axle bearing nuts with a torque wrench. but how fast can i make the car go (or accelerate)? not fast, why, HP is less than 1.
The formula is:
Acceleration=power/(mass x velocity) that tells you at an comparative speed, acceleration is determined by HP at that speed.
How fast you can go is HP. (rate of doing work)
How fast you get there is HP (rate of doing work).
HP is equal to the torque at the rear wheels. engine torque has to be multiplied by gear ratios to mean anything. with HP , the speed element is already built into the term. HP is equal to torque x speed/5250. HP is also equal to Force x MPH/constant. top speed is also limited by aero, and HP to aero ratios are also useful, but to this point, we have left everything else being equal. same car, driver, etc, only powertrain to be varied.
mk
The formula is:
Acceleration=power/(mass x velocity) that tells you at an comparative speed, acceleration is determined by HP at that speed.
How fast you can go is HP. (rate of doing work)
How fast you get there is HP (rate of doing work).
HP is equal to the torque at the rear wheels. engine torque has to be multiplied by gear ratios to mean anything. with HP , the speed element is already built into the term. HP is equal to torque x speed/5250. HP is also equal to Force x MPH/constant. top speed is also limited by aero, and HP to aero ratios are also useful, but to this point, we have left everything else being equal. same car, driver, etc, only powertrain to be varied.
mk
Last edited by mark kibort; 02-17-2009 at 10:18 PM.