Torque versus hp

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smac, Jul 9, 8:39am
Slightly different angle on the ol' torque versus hp debate:

When calculating power to weight ratio most people seem to talk in terms of max hp.

But if trying to compare the relative real-world performance of standard road cars, surely it makes more sense to consider torque!

EG. if you look at MK4 mondeo's on paper, using hp, the 2.3 petrol has a nominally better ratio, being 50kg lighter.

But anyone who's driven both knows the diesel will eat the petrol for lunch 'cause it's such a torque monster through a pretty wide rev range.
turton, Jul 9, 8:58am
torque is definately more important.
tonyrockyhorror, Jul 9, 9:01am
You're comparing peak torque with torque spread through the rev range.

It's better to produce engine torque at higher rpm so that gearing can be utilised to provide more torque at the wheels at the same road speed.
tonyrockyhorror, Jul 9, 9:02am
For what! And from where!
richardmayes, Jul 9, 9:23am
it depends.

Top-end whizz is all very well IF you can keep the revs up in the "power band" where the power is.

But on the road you almost never drive like that, so it's much more useful to have bottom end grunt such that the acceleration continues unabated after you've changed up a gear.

(I found my Triumph PI from the 1970s with 132 horsepower had similar real world on-road performance as a lot of 150-170bhp Jappers of a similar size. because my engine got its peak torque at 2000rpm so just about the whole rev range was "the power band". )

On a racetrack every last horsepower counts, on the road I would take a spread of torque and some decent low-down grunt any day.
bellky, Jul 9, 9:27am
I don't agree. I personally like stump pulling torque from idle.
sr2, Jul 9, 10:16am
You can??
thegravelracer, Jul 9, 10:22am
What a stupid post . The are one in the same HP is a product of torque .Under the curve
bellky, Jul 9, 10:26am
Don't you duds go thinking that you know something that others don't ok. Low down torque is what we're talking about here, so keep your silly hair splitting arguments that are an excuse for an engine with no guts, in the slow lane.
sr2, Jul 9, 10:35am
I think you may find that they are not as you put it "one in the same". Torque is a rotational force that can be applied without movement where as HP is a measurement of potential to do work i.e. it has an element of time in it. And to confuse you even more Shaft HP is the product of torque multiplied by RPM. Basic 5th Form physics!
smac, Jul 9, 11:15am
You guys saying it's the same thing didn't read my post.

I'm not talking about "what is better, HP or torque" cause that's pointless. I'm suggesting that torque to weight is a better representation of a vehicles performance on a real road than hp to weight. As with the above example (mondeo).

If you don't know enough to comment on that, why are you commenting in the thread.
bellky, Jul 9, 11:23am
Fwiw smac I agree with you. You might think I'm dreaming when I say that my 12a stage 2 in a 900kg Rx-2 is very torquey. Rotaries have a reputation for lacking torque when in fact thay are torque rich only that the displacements are small. That engine with that porting etc. in that car makes for a torquey proposition; it really takes off, you can feel it and passengers have commented as much.
tonyrockyhorror, Jul 9, 11:26am
So do I. I'm happy to sacrifice outright peak power for low and mid-range power.

People wrongly confuse 'torque' with meaning low rpm zone. It doesn't mean that at all.
bellky, Jul 9, 11:30am
Yep, there's nothing worse than putting your foot down and having to wait for the turbo to kick in, or for the auto to kick down, or having to change gear, or waiting for vtec etc.
tonyrockyhorror, Jul 9, 11:34am
Stump pulling power is certainly better for daily street driving. There's no use having a peak 180kW on the road if there's only 50kW available in the rpm range where you spend most of your time.

But if you want outright WoT acceleration you want to concentrate on outright power coupled to gearbox ratios that make the most of it.
smac, Jul 9, 1:04pm
The reason I started looking at this is:

As I weigh up cars to replace the trusty Astra with, one thing I wanted to make sure I'm not doing is looking at machines that are even slower than it is.

What I've noticed is a lot of "mid range" cars are so bulky now that even the 2.3 and 2.4 cars are likely to have less power for the weight than the Astra. Pfft.Yes I know transmissions are more efficient these days and they'll be 5 or 6 speed etc, but still.
bellky, Jul 9, 1:22pm
You know apparently there are very few cars the Top Gear twits agree on. one being the Mondeo - they think it's good.
nzdoug, Jul 9, 6:02pm
a n engine can put out different torque via gearing.
smac, Jul 9, 6:05pm
Oh this'll be good.
tonyrockyhorror, Jul 9, 6:21pm
The engine can't. but the gearbox behind it can.
carclan, Jul 9, 6:24pm
P=T x omega
morrisman1, Jul 9, 6:59pm
This is always a goodie.

In the end, it is only torque at the wheels that matters, and how long you can achieve it for. Diesel engines have lots of torque but cant multiply it as much through the gearbox. High revving petrols may not produce as much torque but because of gearing the torque at wheels may be similar.

It all comes down to, do you want a lazy engine or one which is fun to drive.

And please please nobody say that torque makes you accelerate and horsepower gives you top speed haha.
jason18, Jul 9, 8:31pm
Torque makes you accelerate and HP gives you top speed
gunhand, Jul 9, 8:36pm
You wernt allowed to say that.But to go faster dont you need more HP.
Im sure they said with the Veyron, 600hp will make it 350kph but they need 1000hp to make it do 400kph. Or something like that LOL.Figures made up as example only. I dont know excact ones.
morrisman1, Jul 9, 8:47pm
what they were meaning to say is they need 4000NM of torque at the wheel to do 350km, divided by the lever arm between the hub and the road surface in order to achieve enough linear thrust to overcome the aerodynamic and mechanical drag of the vehicle. Then at 400km/h they needed a lot more.