BHP vs Torque?
#42
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to accelerate you need power?????
NOOOOO
Force = mass x acceleration
so you have a car of mass x and you are accelerating at rate y - from somwhere you need a force!!
Torque = force x distance
you need torque to accelerate and nothing else!!!
The result of you having accelerated ie the car is going faster is POWER.
#43
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WHAT?
to accelerate you need power?????
NOOOOO
Force = mass x acceleration
so you have a car of mass x and you are accelerating at rate y - from somwhere you need a force!!
Torque = force x distance
you need torque to accelerate and nothing else!!!
The result of you having accelerated ie the car is going faster is POWER.
to accelerate you need power?????
NOOOOO
Force = mass x acceleration
so you have a car of mass x and you are accelerating at rate y - from somwhere you need a force!!
Torque = force x distance
you need torque to accelerate and nothing else!!!
The result of you having accelerated ie the car is going faster is POWER.
No alex, you are COMPELTELY missing my point.
Lets say you have 500lbft of torque, but only 200bhp for example.
You will hook up at 1000rpm and by 2000rpm you will have to change gear!
You CANT accelerate hard up the strip without big horsepower, end of, no exceptions!
#47
Testing the future
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if gearchanging were seamless and instant and you had no limit on the number of ratios, it wouldn't matter (until you get to the speed where drag = power and you can no longer accelerate)
#50
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No im not, im not ignoring anything at all, I understand the subject FULLY
The moment you change gear to get back in the power band, you have just REDUCED the amount of torque at the wheels.
Thats why you need the torque to continue up the rev range, which is what then results in more horsepower!
#53
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If you are doing 20mph when you change out of first gear on your low revving torquey motor with 500lbft, then by the time you get to 100mph you only have the same acceleration as you would in that first gear with a mere 100lbft if you had the revs to be able to stay in that gear, and you wouldnt have wasted time with lots of gear changes first!
#54
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if you are comparing doing 100 mph in one gear with doing 100mph with many gears, then you are not talking about the same engine capacity
#55
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#57
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Unless you are talking CVT, in which case it does t technically class as a gear change, but as a gearing change, you will ALWAYS have "some" time to change gear on a manual box, so its a pointless statement you are trying to make.
Even more so because as the gearing changes, the torque at the wheels drops linearly, where as if you keep the torque constant up the rev range (different boost curve or whatever to do so) then it will accelerate linearly (bear in mind at the same time it will be resisted by air resistance etc though of course so your linear accelerative force wont equal linear acceleation, but that reduction is the same in both cases)
Thats not the case at all by definition, no one has mentioned capacity at all.
Even more so because as the gearing changes, the torque at the wheels drops linearly, where as if you keep the torque constant up the rev range (different boost curve or whatever to do so) then it will accelerate linearly (bear in mind at the same time it will be resisted by air resistance etc though of course so your linear accelerative force wont equal linear acceleation, but that reduction is the same in both cases)
Thats not the case at all by definition, no one has mentioned capacity at all.
Last edited by Chip; 25-07-2008 at 12:11 PM.
#59
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Engine Transmission output torque (ft-lb):
Torque 1st 2nd 3rd 4th 5th
RPM (ft-lb) 3.54 2.13 1.36 1.03 0.72 <- gear ratio
---- ------- ---- ---- ---- ---- ----
1000 50 177 107 68 52 36
1500 65 230 138 88 67 47
2000 80 283 170 109 82 58
2500 92 326 196 125 95 66
3000 104 368 222 141 107 75
3500 114 404 243 155 117 82
4000 120 425 256 163 124 86
4500 125 443 266 170 129 90
5000 130 460 277 177 134 94
5500* 133 471 283 181 137 96
6000 130 460 277 177 134 94
6500* 122 432 260 166 126 88
7000 110 389 234 150 113 79
From a 2.0 ohc engine with a 5 speed box.
Torque 1st 2nd 3rd 4th 5th
RPM (ft-lb) 3.54 2.13 1.36 1.03 0.72 <- gear ratio
---- ------- ---- ---- ---- ---- ----
1000 50 177 107 68 52 36
1500 65 230 138 88 67 47
2000 80 283 170 109 82 58
2500 92 326 196 125 95 66
3000 104 368 222 141 107 75
3500 114 404 243 155 117 82
4000 120 425 256 163 124 86
4500 125 443 266 170 129 90
5000 130 460 277 177 134 94
5500* 133 471 283 181 137 96
6000 130 460 277 177 134 94
6500* 122 432 260 166 126 88
7000 110 389 234 150 113 79
From a 2.0 ohc engine with a 5 speed box.
#60
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Two simple questions for all.
Anyone with half a brain should be able to see the VERY obvious answers and that should hopefully just end this debate totally, lol
You have a car, it has a CVT gearbox, the revs will remain exactly the same at all times and the gearing will seamlessly vary, its a magical CVT box in that it can do any ratio you want, and it doesnt have any transmission loss to consider.
question 1:
Where on the power curve or torque curve will you set the RPM point the gearbox maintains, for maximum accelration and top speed, is it:
a) at peak torque
b) at peak power
c) where the power and the torque cross
question 2:
If all these engines weight the same etc, which will provide better acceleration AND a high top speed in our car (after the gearbox has been set to optimum for each one):
a) 1,000 lbft, 200bhp
b) 500 lbft, 300bhp
c) 250 lbft, 400bhp
Thankyou, please come again
Anyone with half a brain should be able to see the VERY obvious answers and that should hopefully just end this debate totally, lol
You have a car, it has a CVT gearbox, the revs will remain exactly the same at all times and the gearing will seamlessly vary, its a magical CVT box in that it can do any ratio you want, and it doesnt have any transmission loss to consider.
question 1:
Where on the power curve or torque curve will you set the RPM point the gearbox maintains, for maximum accelration and top speed, is it:
a) at peak torque
b) at peak power
c) where the power and the torque cross
question 2:
If all these engines weight the same etc, which will provide better acceleration AND a high top speed in our car (after the gearbox has been set to optimum for each one):
a) 1,000 lbft, 200bhp
b) 500 lbft, 300bhp
c) 250 lbft, 400bhp
Thankyou, please come again
Last edited by Chip; 25-07-2008 at 12:24 PM.
#64
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My car is fast & it acclerates cos of its flat Torque curve you are only on peak Power once in every gear. Seen dozens of torque less wonders struggle down brunters & not reach 180 telling everyone about their 600bhp no torque shite. Mine held the RWD Topspeed record down Brunters with 480bhp but with 500ft-lb torque.
Chip get back to IT leave this stuff to the likes of Colin Chapman.
#65
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My car is fast & it acclerates cos of its flat Torque curve you are only on peak Power once in every gear. Seen dozens of torque less wonders struggle down brunters & not reach 180 telling everyone about their 600bhp no torque shite. Mine held the RWD Topspeed record down Brunters with 480bhp but with 500ft-lb torque.
Chip get back to IT leave this stuff to the likes of Colin Chapman.
Chip get back to IT leave this stuff to the likes of Colin Chapman.
Rod your car was well fairly suited to your gearing at 180mph, with different gearing and 400lbft and 600bhp it WOULD be faster at brunters than with 480 and 500, and Colin Chapman (or even mark shead I suspect, lol) would agree with me on this one
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If you are comparing two 500bhp engines, then the one with more torque is likely to have a flatter curve and hence be quicker, but a car with more power and less torque would beat you, thats how physics works.
And by having more power, I mean ACTUALLY having, not claiming, lol
#66
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#68
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I have experience of this as i own a german car with more torque than bhp 516ft/lb to be precise,i also own an italian car with more bhp than torque,by far the easier nicer to drive is the german car with limitless power from 2000rpm,the other has to be driven hard which is a bind unless you are on a race track and flat out most of the time.
#71
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question 1:
Where on the power curve or torque curve will you set the RPM point the gearbox maintains, for maximum accelration and top speed, is it:
a) at peak torque
b) at peak power
c) where the power and the torque cross
question 2:
If all these engines weight the same etc, which will provide better acceleration AND a high top speed in our car (after the gearbox has been set to optimum for each one):
a) 1,000 lbft, 200bhp
b) 500 lbft, 300bhp
c) 250 lbft, 400bhp
Question2 - Top speed will be c)
Best acceleration would be a in theory be a), but you'll probably find it weighs well over 7.5tonnes and is limited to 56mph (1000lbft at 1050rpm
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On the road b) would be the best all rounder as it has good midrange
On the track I'd probably fancy c) as it has good torque high up.
The simlpe answer to this is----
Most (highly tuned cars excepted) have max torque lower down in the rpm range say 3.5-4.5Krpm Max power can be from say 6200rpm upwards on 16V motors.
Take your car down the drag strip and do 2 runs.
Run1 change gear at your max torque rpm
Run2 Change gear at your max power rpm.
See which is quicker down the strip. I know which one I'll put my money on.
Where does any car make it's theoretical top speed? at the Max power rpm or max torque rpm?
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Last edited by Fast Guy; 25-07-2008 at 07:51 PM.
#74
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I like the low down grunt of my car, makes 483 lb/ft
Revs quite well for a V8 i thought, got bloody long gearing though, does about 80/85mph in second. Wouldn't mind changing the rear diff to 3.9 or 4.11
Revs quite well for a V8 i thought, got bloody long gearing though, does about 80/85mph in second. Wouldn't mind changing the rear diff to 3.9 or 4.11
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#80
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utter utter bollocks.
Typically to maximise acceleration you change up shortly after peak power, if you change up at peak power, the revs will drop too far going into the next gear and you wont be back on it hard enough, so you rev past.
If you want to get slightly technical, you should plot the torque curve multiplied by the gearing out for each gear, and change just ever so slightly after they cross.
Typically its about 500-1000rpm past peak power, but that really is a huge generalisation of course.
Typically to maximise acceleration you change up shortly after peak power, if you change up at peak power, the revs will drop too far going into the next gear and you wont be back on it hard enough, so you rev past.
If you want to get slightly technical, you should plot the torque curve multiplied by the gearing out for each gear, and change just ever so slightly after they cross.
Typically its about 500-1000rpm past peak power, but that really is a huge generalisation of course.