Samarth 619

Torque is just "force" applied on anything. If I push a train, I'm applying some torque, even though the train might not move even 1mm.

Power is force combined with the movement caused due to that force.

So, at zero movement, power will always be zero, while torque may not be theoritically.


For example, 5 NM @ 2000 rpm makes lesser speed and drive than 5 NM @ 14,000 rpm. Because the engine itself is rotating higher. At any point of time, more rotations mean more speed, other factors assumed constant.

saipranav

@samrath
but an engine which produces 5NM torque @ 2k rpm will be at a very high speed @14k RPPM when compared to the engine producing 5NM at 14k rpm... am i right?

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abhiiceman

lol AFAIK more torque means more pulling power i.e R15(15NM) with pillon is slower then p220(19NM) with pillion and thunderbird(~28NM) with 3people pulls faster then the other two bikes....

and bhp may be top speed dont knw exactly....
correct me if im wrong dont ROFL..

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abhiiceman

if we go according to that formula then bike with 13nm torque like p150 produce around 22bhp @ 9krpm which doesn'nt make any sense..

someone please explain this..
p220 specs..
MAX TORQUE=19.12@7000rpm
MAX POWER=21.04@8500rpm

so if we calculate bhp using tat formula then p220 should hav 25.22bhp...so please explain...

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Samarth 619

To explain my last post, I was assuming that the SAME engine makes 5 NM @ 2000 as well as 5 NM @ 14000 rpm too. (It is very much possible)

In that case, its speed at 14000 rpm would be more than at 2000 rpm (EVEN THOUGH TORQUE IS SAME). This is the concept of "Power". Its associated with work done/ movement caused.

Am I clear?

You're right about torque. No matter what bike you have, you should be near the max torque spot rpm too. I mean, an R15 @ 7000 rpm is still better than P220 @ 3000 rpm.

Max Power figure affects both acceleration and top speed. Gearing also affects both these figures.

So, when you rev your bike near its redline, you experience a push of power, that translates to good acceleration or high top speed. But the "push" is there...

That formula? Ok, torque changes according to rpm, ok?

In other words, the P150's example considered, 13 NM torque is produced at around 6000 rpm ONLY, not beyond that. Beyond that, while rpm keeps increasing, but torque keeps decreasing slowly.

So, you can't use 13 NM (@ 6000 rpm) figure for something measured at 8000 rpm ie power. For that you'll need torque @ 8000 rpm which will be lower than 13 NM.

Power = (Torque at "N" rpm) X ("N" rpm). N can be any rpm the engine travels at...

So as you rev beyond 6000, when torque is dropping down slowly and rpm is getting higher, the maximum power is produced at around 8000 rpm (can differ for other engines). Beyond 8000 rpm, the torque drops to such a level that increasing rpm can't make more power.

So, when you drag race, you rev it a bit beyond max power spot and then shift the gear up, and pass through the same max power zone again and shift up and so on....

See a torque and power figure to understand power, torque and rpm:



The torque is the yellow line that is maximum at 3400 rpm.. Then it starts decreasing as rpm keeps increasing... RPM X Torque curve is made which tops at 4800 rpm. This is the power.

abhiiceman

i was talking abt that power=(torque*current rpm)/5252...

so torque drops after some particular rpm depending on the vehicle,but still why people shift gears at redline during DRAG?..

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Samarth 619

Yes I understood the formula after some thinking & replied accordingly.

Red lining is not always a measuring point for shifting in drags. Passing through the "Maximum Power" spot while revving is necessary.

Example: You rev your P220 upto 9500 rpm and then shift. When you shift your rpm drops to 8000. Then you rev it upto 9500 and shift into 3rd and rpm drops to 8000 again. By this process, you pass through the max power spot (8500 rpm) multiple times and gain maximum drag.

Consider a different scenario: You're racing on a circuit and revving around 9000 rpm, and there's a corner closing ahead where before turning, you have to downshift for sure.
You have 2 choices:
1. keep revving in the same gear beyond 9500 rpm upto 10500 rpm or so and then downshift as corner approaches,
2. shift up at 9500 rpm and immediately, shift down again as corner is too close now,

What will you choose?

Obviously here, the 1st choice (to keep revving until we approach the corner and then downshift) is better as shifting takes up valuable time and power.

Its called "overrun". That's why some Supersports 600's have their rev limiter very high up even when they make maximum power @ 14 krpm.
For example, rev limiters of the 2007 ZX 6R (16.5 krpm) and 2007 YZF R6 (17 krpm approx).

madhavparashar

Consider a scenario of a gradient, say, going up a treacherously inclined slope. You tend to down shift to prevent your engine from stalling. You go for a smaller gear ratio which provides more torque (pulling force) and less power.

The graph in the post above is for a single gear. On a very treacherous uphill, your best chance to overcome it is @3800 rpm in the first gear. If the engine stalls at that, there is no way you can go past that incline.

Power band funda was beautifully explained in the previous post, why racers on a straight road go for gear shift just above max power rpm.

asif

As simple as i understand, torque is something that helps you to get from zero to running and power is something that helps to maintain that running.

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rachitkdogra

The simplest definition that I have come across and that has made me understand is this.

The real power of the engine is actually the Torque. By power I mean the pulling power. How quickly this power is put to road is BHP.

Trucks have huge Torque but low BHP. Super Bikes have lower torques (They dont need much) but very high BHPs.

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