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torque and power 

 

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 Post subject: torque and power
Posted: Fri Jul 22, 2005 9:39 pm 
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ok - so another thread doesnt get completely hijacked here are some facts on torque and power...

What follows applies to cars with similar power bands. Its no use comparing a blown big block against a NA 6.

power is just the amount of torque at a specified rpm. The formula for working out the power is

power = torque * rpm / 5252

Why 5252? it is what you get when you take all the physics formulas and do half the calculations. Note that this formula is not dependent on the cubic capacity of the engine at all. So a 4.0 making 150rwkw at 5000rpm has exactly the same torque as a 5.0L making 150rwkw 5000rpm, at 5000rpm (this is a bit of a mouthful).

So how does engine capacity figure into this?
Bigger cubic capacity engines generally produce more torque earlier, hence make power earlier, but to make peak power the engine has to be able to sustain its torque curve throughout the rev range. Just because a bigger capacity engine has more torque, that doesnt mean it will go any faster.

How does this apply to drag racing?
When drag racing, you want power. High peak power means you can sustain your torque longer, hence hold gears longer. Also the car is getting driven in a very narrow rev range (say 3500 to 5500), so having a broad power curve doesnt matter, it all comes down to peak power.

who cares how long you hold gears for when you have a torquey engine?
The torque that is applied to the wheels = your engine torque multiplied by the gear ratios of the gearbox and diff. So when you shift gears, you are going to effectively lose a hell of a lot of torque. Unless something crazy is going on in your engine bay, you are always going to accellerate faster in a lower gear than a higher gear for as long the engine can take it (basically up to and a bit past peak power). So by shifting to maximise torque you car will go slower than if you shift to maximise power.

 

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Posted: Fri Jul 22, 2005 9:42 pm 
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oh, and of course changing gear ratios alters all this, but since most falcons have pretty similar ratios this shouldnt matter to much.

 

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Posted: Fri Jul 22, 2005 10:09 pm 
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the 5ltr will have a higher torque figure if it did not it would be pointless having a f**k 5lt

how do you figure it will be same

i am saying it will be higher and usually a higher torque figure will help to quicker times than a car with same kw and less torque IF cars are simmilar or same in weight

f**k its not hard to understand


ok a ba na 6 187 or what not has nilly 400 torque
vz 6 192 or so kw still has lees torque BECAUSE THE CUBES ARE LOWER

DAM IT MAN GO YOU NOT UNDERSTAND


yet a VZ is Faster this comes to weight being a factor which is not what im arguing

 

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Posted: Fri Jul 22, 2005 10:16 pm 
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if torque does not matter then why are turbos fast COS THEY MAKE f**k LOADS OF TORQUE

definition
TORQUE - IS PULLING POWER THE ABILITY TO MOVE WEIGHT


KIllowatt - WANK FACTOR - of course you need it but its not what gets the car going

you can have 200 kw out of a 2lt but it aint gonna have a lot of torque and it is not going to run a quick time unless its in a gocart


do you hear of naturally aspirated 148 rwkw 2ltr cars pulling 14 second passes

definately not in a big heavy car

 

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Posted: Fri Jul 22, 2005 10:17 pm 
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*gets popcorn out*

This is going to be good :) Lets try and play nice.. no need to swear or get personal! :roll:

 

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Posted: Fri Jul 22, 2005 10:19 pm 
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Power is a mathematical equation which as you stated is derived from Torque * RPM / 5252 (which results in a horsepower figure).

Capacity and efficency of the engine plays a major roll in the final mathematical equation.

Example.

Car A requires 15000rpm to create 100hp, and Car B requires 1500rpm to create the same 100hp... What do you think is going to accelerate faster?

Dont preach, if you dont understand it!

 

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Last edited by South on Fri Jul 22, 2005 10:25 pm, edited 2 times in total.

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Posted: Fri Jul 22, 2005 10:19 pm 
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so a 150kw 4.0lt has same torque at 5000rpm as a 5.0tl so does that work with a 3.0ltr its only a litre difference from a 4.otlr and i guess a 5.0lt has same torque at 5000rpm as a 6.0lt or 6.7 litre

 

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Posted: Fri Jul 22, 2005 10:23 pm 
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*Popcorn, Popcorn, get your fresh Popcorn, Only $1 a bucket, Popcorn, Popcon*

 

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Posted: Fri Jul 22, 2005 10:26 pm 
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South wrote:
Car A requires 15000rpm to create 100hp, and Car B requires 1500rpm to create the same 100hp... What do you think is going to accelerate faster?


Depends on the gearing, car A allows for a much shorter diff gear as the engine can rev higher. Both of these cars can apply the same amount of torque to the rear wheels if the correct gearing is provided (give or take drivetrain losses which are associated with different gear ratios).

So essentially, both of these cars should be equal? :D

 

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Posted: Fri Jul 22, 2005 10:27 pm 
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South wrote:
Power is a mathematical equation which as you stated is derived from Torque * RPM / 5252 (which results in a horsepower figure).

Capacity and efficency of the engine plays a major roll in the final mathematical equation.

Example.

Car A requires 15000rpm to create 100hp, and Car B requires 1500rpm to create the same 100hp... What do you think is going to accelerate faster?

Dont preach, if you dont understand it!


both same but what im saying is 2 different sized engines cannnot have same kw and same torque there is goin to be a difference especially over 4tl to 5tl

 

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Posted: Fri Jul 22, 2005 10:27 pm 
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sickd wrote:
if torque does not matter then why are turbos fast COS THEY MAKE f**k LOADS OF TORQUE

definition
TORQUE - IS PULLING POWER THE ABILITY TO MOVE WEIGHT


KIllowatt - WANK FACTOR - of course you need it but its not what gets the car going

you can have 200 kw out of a 2lt but it aint gonna have a lot of torque and it is not going to run a quick time unless its in a gocart


do you hear of naturally aspirated 148 rwkw 2ltr cars pulling 14 second passes

definately not in a big heavy car


sickd wrote:
the 5ltr will have a higher torque figure if it did not it would be pointless having a f**k 5lt

how do you figure it will be same

i am saying it will be higher and usually a higher torque figure will help to quicker times than a car with same kw and less torque IF cars are simmilar or same in weight

f**k its not hard to understand


ok a ba na 6 187 or what not has nilly 400 torque
vz 6 192 or so kw still has lees torque BECAUSE THE CUBES ARE LOWER

DAM IT MAN GO YOU NOT UNDERSTAND


yet a VZ is Faster this comes to weight being a factor which is not what im arguing


i think you have both completly missed the point of this.

yes torque is what gets you down the road.

and as you say power is wank.
but power is calculated from torque.

every one talks about torque being th down low pulling power and KW or HP being the up high pulling power.

the reality is torque is the pulling power every where in the revs.
and power is just a number found using simple math.

and it where in the revs that there is more torque, that determins how QUICK your car is.


a good example of all of this is putting an EF XR6 next to an EF XR8
and we all know what happens there the V8 gets left behind. yet it has more torque lower in the revs.


Quote:
the 5ltr will have a higher torque figure if it did not it would be pointless having a f**k 5lt

how do you figure it will be same


he never said it would be that same peak torque.

he said if both engine make 150kw @5000 rpm that both engine would have the same torque AT THAT RPM it's all in the math and you can't argue with it

 

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Posted: Fri Jul 22, 2005 10:30 pm 
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Assume car A is only efficient from 13000rpm to 16000rpm, whereas car B is efficient from 800rpm to 2000rpm :D

 

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Posted: Fri Jul 22, 2005 10:32 pm 
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its also heavier and has 3.27 gears makes a hell of a difference , the t5 box is also geared to help the xr6

 

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Posted: Fri Jul 22, 2005 10:32 pm 
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South wrote:
Assume car A is only efficient from 13000rpm to 16000rpm, whereas car B is efficient from 800rpm to 2000rpm :D



then if both cars had the same torque, car A would have a s**t load more power and would s**t all over car B

 

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Posted: Fri Jul 22, 2005 10:33 pm 
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South wrote:
Assume car A is only efficient from 13000rpm to 16000rpm, whereas car B is efficient from 800rpm to 2000rpm :D


which goes to show different engine size

 

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