Cosworth427

Torque multiplication is a huge misconception...

With internal combustion reciprocal engines, we are faced with two problems.

1) Power is not linear through the RPM range of a street car engine.

2) Street car engines have limited RPM range.

Acceleration is just the natural rate of an object reaching a desired speed vs resistance. You *require* enough power to reach a specific speed, and extra power you have means greater acceleration. A 500 HP engine in a 1500 KG car provides plenty of extra power, say from 0 - 180 MPH.

But car engines cannot make maximum power through out it's entire RPM range. If it did, we would not need more than 2 gears (forward and reverse). So this is where multiple gears comes in. A theoretical 1:1 ratio means that the crankshaft rotation speed will match the rotation speed of the driving wheels. Its alot like trying to launch a car in top gear, but even worse than that since there is a final drive gear.

With a set of step down gears, you can make sure that whatever speed you are launching or accelerating from and to, the engine will be operating at an RPM where it is making sufficient power. It is simply mapping engine RPM to the car's intended MPH. The closer to the RPM where maximum power is made, the greater the performance.

Torque multiplication is misunderstood because the fact that multiplying torque does NOT increase or decrease power/work. A car does not directly accelerate faster because of more multiplication, it accelerates faster from shorter gearing because it places car velocity closer or within the RPM range where most power is made.











[Edited by Cosworth427 - 11/28/2003 1:03:25 PM]

Nick100

Interesting subject, but my head hurts
I'm off to the pub

HotRod

A steam engine has loads of torque, and its torque peaks at zero RPM when the thing has built up just enough pressure to start the piston moving. Once a steam roller gets going it has no gears and torque drops so its dead slow.
Don't know where this is leading.... I'll get my coat..

greasemonkey

Electric motors have their torque peak at 0 rpm as well. The unit in the Toyota Prius develops over 530lb/ft!

macka

Jesus!

IMHO

Lots of BHP, low torque = car feels like hard work to drive and not as fast as it really is.

Lots of torgue, low BHP (diesel) - car fels quick in the mid range but doesn't go any faster when you rev it.

Best is big bore, high BHP and high torque petrol engine, supercharged and turbo charged to get low down efficiency and grunt and high revving performance - like the old banned rally cars!! Best of all worlds

matty01

.

matty01

Right i'll have a go...power/BHP is a representitive term for the willingness of the engine to increase revs whilst under load,torque is the represintitive term for the force that the engine can produce at a given revs.....for example, a cheetah is powerfull but not very torquey,whereas an elephant is really torquey but not powerfull,the cheetah would be a superbike (really powerfull but not particularly torquey)that only has to shift a light weight,the elephant would be a HGV/van/truck (usually a bit more torque than power)that has to pull and maintain a steady force(eg. up hills with a heavy cargo)which is what torque is good at.A really torquey car won't be all that quick if it hasn't got 'enough' power, as it wont rev quick enough ,so allthough torque makes a car nice and easy to drive the engine also needs enough power to'move you up the road a bit' not just 'pull like a train'.
I think that about sorts it...

Trashman

So likening it all to animals, a car is obviously a SIAL?

I'll get me coat

mik

Thankyou very much.

Link made clicky CLICK ME NOW


The same article (more or less - I added a particular ref to scoobs) was published in the SIDC mag last year mate.

[Edited by mik - 11/29/2003 8:04:38 AM]

[Edited by mik - 11/29/2003 8:06:02 AM]

DMC12

I found this explained it quite well.

matty01

Doesn't exactly roll off the tongue though does it
Corner..

[Edited by matty01 - 11/29/2003 2:03:10 PM]