Which is faster horsepower or torque?

[kambites]

Yes, torque (or more precisely low-rev power or if you want to be really pedantic low-rev, high-gear wheel-torque) is important if you want to go fast but can't be bothered to change gear.

[Patrick Bateman]

The_Burg said:

Don't turbos and superchargers make these calculations irrelevant? A fairly low powered turbo can produce huge torque and be in the zone in most normal driving conditions be on the power?

A 100hp turbo can produce torque that would require a much bigger NA engine.

One of the reasons most modern diesels can destroy a petrol car if you can't be arsed to change gear?

It just means more of its power is available lower in its rev range.

[Jayfish]

Is it on a conveyor belt?

[mikearwas]

kambites said:

If you only have one gear, the maximum G-force will be pulled at peak torque. If you can alter gears, you always want to be in the gear that puts you at the highest power figure possible.

Basically, if you're in third gear, your car will accelerate harder from 40mph than it will from 80mph but if you're doing 40mph, your car will accelerate hardest in second gear not third.

I'm not sure I understand this. If you take your 80mph and make it 50mph in third surely the car will accelerate harder because it will be nearer peak power/revs?

[kambites]

mikearwas said:

I'm not sure I understand this. If you take your 80mph and make it 50mph in third surely the car will accelerate harder because it will be nearer peak power/revs?

Yes it will, but not as hard as it would if you were at 50mph in second gear, despite the fact you're further from peak torque in second. Work out the wheel torque in each gear and it becomes much more obvious.

[mikearwas]

kambites said:

Yes it will, but not as hard as it would if you were at 50mph in second gear, despite the fact you're further from peak torque in second. Work out the wheel torque in each gear and it becomes much more obvious.

Ah I see what you're saying. Therefore max acceleration in each gear will effectively occur at a fixed speed?

[Captainawesome]

VBRJ said:

Owner of petrol car: "Power"

Owner of diesel car: "Torque"

Typical PHer: "Remapped 335/MX5"

Fixed for ya

[Captainawesome]

A car is as fast as it's driver regardless of any figures, unless the figure in question resembles an hourglass and is waiting at the end in which case the car will be as quick as goddamn possible.

[CrutyRammers]

Ah, good to see this topic being as entertaining as it usually is

[Kozy]

Aww geez, not this st again.

Power = force x velocity.

Forget the engine there, and think wheel torque and vehicle speed.

If you made a constant 600bhp (447kW, lets make it 450kW for simplicity), your drive thrust would would be:

10m/s = 45kN
20m/s = 22.5kN
30m/s = 15kN
40m/s = 11.25kN
50m/s = 9kN
60m/s = 7.5kN
70m/s = 6.4kN
80m/s = 5.6kN
90m/s = 5kN
100m/s = 4.5kN

Same with 400bhp (300kW)

10m/s = 30kN
20m/s = 15kN
30m/s = 10kN
40m/s = 7.5kN
50m/s = 6kN
60m/s = 5kN
70m/s = 4.3kN
80m/s = 3.75kN
90m/s = 3.3kN
100m/s = 3kN

What is described there is the thrust curve, and the torque is irrelevant in it's calculation. Engine torque only matters if you're in the wrong gear.

Edited by Kozy on Tuesday 14th January 10:15

[james_gt3rs]

McWigglebum4th said:

Okay lets ask another question

What is faster

My wives fiat panda which produces about 80lb/ft of torque at 5000rpm


Or a scaffolding pole which is lighter then the panda by about 800 kgs but it produces with me hanging off the end well over 1000lb/ft of torque at zero rpm

Fighting fire with fire

[Kozy]

Here's what a thrust curve looks like for the suggested comparison

With a constant torque figure and gearing such that each vehicle has the same vmax in each gear.



It's pretty obvious which one is the 600bhp/400lbft trace. Note how 600lbft is no advantage at any point.

Here's 600bhp/400lbft vs 600bhp/600lbft, again with gearing set for identical speeds in each gear.



Torque is irrelevant.

[blugnu]

I think it's whichever car is loudest, least reliable and most expensive.

[biscione]

HP init

[kambites]

XJ Flyer said:

Engines don't work by running at constant peak power and what matters is the amount and spread of torque and therefore how much power the engine is producing throughout it's rev range which is what determines how quick it'll accelerate the car up to peak power.In all cases,by definition,it's the 'torque curve' which determines the power outputs being that by 'curve' we're referring to the torque figure related to engine speed.

The amount of torque (or power, they are equivalent in this context) generated in the part of the rev range used for optimal acceleration, which in 99% of engines doesn't include the bit of the rev range where peak torque is generated. Thus peak torque is utterly irrelevant to performance. Peak power is relevant but does not tell the whole story (unless you have a CVT, in which case it does).

[Kozy]

XJ Flyer said:

Engines don't work by running at constant peak power and they wouldn't last long even if they did

You've never seen a WRC car dyno plot then. Pretty constant 300bhp through most of the rev range.

In fact, most new turbocharged petrol performance cars have a constant power output from around 4500rpm to 6500rpm. You'll be changing gear between those two points, so again, constant power.

It's not as ridiculous a concept as it sounds.

Edited by Kozy on Tuesday 14th January 10:39

[thatdude]

blugnu said:

I think it's whichever car is loudest, least reliable and most expensive.

Don't forget the go-faster stripes.

[trashbat]

Kozy said:

You've never seen a WRC car dyno plot then. Pretty constant 300bhp through most of the rev range.

In fact, most new turbocharged petrol performance cars have a constant power output from around 4500rpm to 6500rpm. You'll be changing gear between those two points, so again, constant power.

It's not as ridiculous a concept as it sounds.

Edited by Kozy on Tuesday 14th January 10:39

Erm... can you demonstrate this?

[otolith]

Kozy said:

You've never seen a WRC car dyno plot then. Pretty constant 300bhp through most of the rev range.

Purely an artificial result of the technical regulations, though. 300bhp isn't much for a 1.6 running 4-5 bar - remove the intake restrictor and see what can be done then.

[Kozy]

trashbat said:

rm... can you demonstrate this?

Demonstrate what?

Go look at a multitude of new petrol turbo cars. Lots will have a torque figure higher than the power, and the peak power will be around 5k, yet they rev to 7k.

The torque is dropping at the same rate the revs are rising, effectively keeping the power output capped. It makes the cars feel much faster than they are and is a depressing trend amongst new cars.