Is torque really relevant?

[Equus]

otolith said:

I think there might be one or two people on here who sat a maths A-level as a teenager and aren't too terrified by calculus, maybe give it a go?

a) I don't have the time.
b) I don't have the inclination.
c) I wouldn't even know where to begin in presenting the necessary mathematical notation with the text limitations on this forum.

Those who are saying 'there's no difference' simply need to think about it a bit: it feels different, because it is different.

Since both you and Kambites are 'Elise' men, look at it empirically: if torque made no difference, why did Lotus bother with the option of a close ratio gearbox, and why did everyone who drove the K-series Elise, so equipped, say that it transformed the car?

We all know and (presumably?) accept that power is a function of torque and revs. A close ratio gearbox works by better matching the revs side of that equation (but has negative side effects in that it necessarily leaves you with either a tall first gear, or a short top gear - or both)... a diesel simply does the same by delivering on the torque side, while keeping the spread of ratios.

[Fastdruid]

donkmeister said:

John Locke said:

Baldchap said:

This tends to result in better throttle response and,

One quality which a diesel, indeed any turbocharged engine doesn’t have is good throttle response. For that a naturally aspirated or supercharged petrol engine is needed, or better, an electric motor.

I would go further and say that throttle response on modern engines is often misleading under normal circumstances. All the mainstream brands do it... You pick up the car, you drive a couple of miles and think "this feels peppy!". Then you get to a sliproad, floor it and find that what you thought was a moderate press of the throttle was actually full throttle.
It's like they've figured out that most drivers never pushed the pedal all the way so maximum power demand is in the first half of the pedal travel.
So OP, whatever you try, make sure you actually floor it a few times on your test drive.

This used to really infuriate me on the RX-8, there was very very little difference between 3/4 and full throttle. To the extent that it felt kind of broken when you went for full throttle because you were expecting 25% more and instead you got maybe 5%.

[Fastdruid]

RonaldMcDonaldAteMyCat said:

If petrols are now as full of emissions gubbins and complexity as their diesel equivalent, and hence prone to similar risk of breakdowns, and all other things being equal, I'd probably prefer the diesel if my driving was mainly out of town and the petrol if it was urban.

Every similar technology is more reliable on a petrol. DMF, DI, (D)GPF, turbo's. All are either under less stress, work better and don't have the same issues as they do in diesels. Any unreliability is more due to a mere bad implementation than any inherent problem.

For example just about every single petrol car since the 90's has had a DMF, except people don't realise because how many times do you hear of a petrol DMF failing? At the same time almost every manual diesel owner has either experienced DMF failure or at least heard of the risks.

[Gad-Westy]

julian64 said:

J4CKO said:

How much power and torque is required to "Make Progress" ?

Good question.

Down A roads with good sight you only need more than the car you are about to overtake, or their co-operation.

Down B roads with poor sight I like 600nm or 400 bhp. Don't mind which of those two you give me.

This should do you nicely

[anonymous-user]

Olivergt said:

rockin said:

A quick tap will change the car down with no significant change of engine rpm.

Can you explain how a gear change won't result in a change of engine rpm? Or maybe I'm not quite understanding correctly?

Your bold text was a bit too wide - see narrower adjustment above. An 8 speed auto has the ratios pretty close together and you can change down a gear with a slight twitch of the foot and limited rpm alteration. It's not "plant the throttle, wait for the engine to build torque, wait for the transmission to realise it's being asked to do more work and change down a gear with revs heading for the sky". Modern ones can be fast and sensitive.

[julian64]

Gad-Westy said:

julian64 said:

J4CKO said:

How much power and torque is required to "Make Progress" ?

Good question.

Down A roads with good sight you only need more than the car you are about to overtake, or their co-operation.

Down B roads with poor sight I like 600nm or 400 bhp. Don't mind which of those two you give me.

This should do you nicely

probably should have qualified that a bit to say it needs to be in something aerodynamic and under two tonne

[J4CKO]

julian64 said:

J4CKO said:

How much power and torque is required to "Make Progress" ?

Down B roads with poor sight I like 600nm or 400 bhp. Don't mind which of those two you give me.

Ahh Mr Cummings !

I just get an eye test and can make do with less power as I can see what's coming before I pull out

[kambites]

There's no calculus involved, it's basic newtonian mechanics, although the inertial moment of force in the engine is probably more easily expressed in a Lagrangian frame of reference.

As I said I have worked it out in the past as best I could and the difference is negligible, at least it was for engines I chose. Inertia in the engine is a tiny fraction of the inertia of the body of the car anyway.

Anyway as any physicist will yell you, if your theory tells you one thing and empirical evidence tells you another, you come up with a new theory. There are numerous examples of diesel and petrol examples of the same car with the same power but very different torque figures having damned near identical performance.

Edited by kambites on Monday 6th July 18:50

[RobM77]

Fastdruid said:

donkmeister said:

John Locke said:

Baldchap said:

This tends to result in better throttle response and,

One quality which a diesel, indeed any turbocharged engine doesn’t have is good throttle response. For that a naturally aspirated or supercharged petrol engine is needed, or better, an electric motor.

I would go further and say that throttle response on modern engines is often misleading under normal circumstances. All the mainstream brands do it... You pick up the car, you drive a couple of miles and think "this feels peppy!". Then you get to a sliproad, floor it and find that what you thought was a moderate press of the throttle was actually full throttle.
It's like they've figured out that most drivers never pushed the pedal all the way so maximum power demand is in the first half of the pedal travel.
So OP, whatever you try, make sure you actually floor it a few times on your test drive.

This used to really infuriate me on the RX-8, there was very very little difference between 3/4 and full throttle. To the extent that it felt kind of broken when you went for full throttle because you were expecting 25% more and instead you got maybe 5%.

Many cars are like this. Plus many sports cars and hot hatches have an annoying habit of making the throttle too sensitive in the first inch or so; it's done so numpties think the car's faster than it really is, but plays havoc with trying to drive properly fast because it's so hard to be smooth. They do the same with steering too.

Plus, with a modern car it's not actually throttle the pedal governs, it's power/torque demand. So if you floor it at 1200rpm it doesn't fully open the throttles, it gives you the throttle opening that generates the maximum torque. I'm far happier with carbs to be honest.

[Jag_NE]

The current 530d is absolutely brilliant imo, almost a perfect all round package. OP, have you looked at used ones as the 530d seems to depreciate more severely than other models, particularly if you are happy with SE spec.

[MC Bodge]

RobM77 said:

I'm far happier with carbs to be honest.

A set of four well-setup carbs on a bike is brilliant. It's very satisfying when you manage to set them and balance them well.

My last carb'd bike, aFazer 600, was even very economical too.

[kambites]

MC Bodge said:

A set of four well-setup carbs on a bike is brilliant. It's very satisfying when you manage to set them and balance them well.

It is on a car too, as long as you're as happy tinkering as driving. I would never go back to carbs on a daily driver, but for a pure toy, there's something hugely appealing about them.

[anonymous-user]

RobM77 said:

Plus, with a modern car it's not actually throttle the pedal governs, it's power/torque demand. So if you floor it at 1200rpm it doesn't fully open the throttles, it gives you the throttle opening that generates the maximum torque. I'm far happier with carbs to be honest.

If you like your carbs that's fine. Bear in mind they typically deliver peak grunt by hefty over-fuelling. In my old Esprit when you mashed the throttle pedal the accelerator pumps on the twin Dell'Ortos just dumped a ton of fuel into the cylinders. You didn't need the choke to cold start the car - a stab of the accelerator before cranking covered that ground. By the same token a stab too many would leave the engine flooded with fuel and a b***h to start.

Yes, the modern throttle pedal is an electronic "torque controller", very different in concept from a Bowden cable attached to a butterfly valve at the engine intake - and an accelerator pump.

[ddom]

rockin said:

. Bear in mind they typically deliver peak grunt by hefty over-fuelling..

Since when has ‘peak’ power been delivered running rich?

[Fastdruid]

ddom said:

rockin said:

. Bear in mind they typically deliver peak grunt by hefty over-fuelling..

Since when has ‘peak’ power been delivered running rich?

It's not but when you open the throttle on a carb you make the mixture suddenly very lean. Hence accelerator pumps of various types that squirt a slug of fuel when you snap the throttle open.

[Gary C]

Equus said:

otolith said:

I think there might be one or two people on here who sat a maths A-level as a teenager and aren't too terrified by calculus, maybe give it a go?

a) I don't have the time.
b) I don't have the inclination.
c) I wouldn't even know where to begin in presenting the necessary mathematical notation with the text limitations on this forum.

Those who are saying 'there's no difference' simply need to think about it a bit: it feels different, because it is different.

Since both you and Kambites are 'Elise' men, look at it empirically: if torque made no difference, why did Lotus bother with the option of a close ratio gearbox, and why did everyone who drove the K-series Elise, so equipped, say that it transformed the car?

We all know and (presumably?) accept that power is a function of torque and revs. A close ratio gearbox works by better matching the revs side of that equation (but has negative side effects in that it necessarily leaves you with either a tall first gear, or a short top gear - or both)... a diesel simply does the same by delivering on the torque side, while keeping the spread of ratios.

The only torque that counts is the torque applied at the wheel hub, all the rest is about getting it there.

Engine torque figures are meaningless without factoring everything else. I can generate 160 Nm at the crank on my pushbike !

Power is better as it factors in torque and revs but still doesn't tell the full tale.

But personally, I much prefer a low torque high rev engine to any diesel.

[Gary C]

ddom said:

rockin said:

. Bear in mind they typically deliver peak grunt by hefty over-fuelling..

Since when has ‘peak’ power been delivered running rich?

Merc 500SL lost power in the 90's when it lost its overfuel facility. Rather than ensuring complete burn, it needed to overfuel and run a bit rich to get the best BMEP, which resulted in some fuel not being burnt.

So yes, peak power can be delivered 'rich'

[Corvid-2020]

Gary C said:

But personally, I much prefer a low torque high rev engine to any diesel.

3000 rpm "steam" engines, 800,000 hP Gary?

Although I must admit my favourite engine every to drive was a "diesel" and that was a bit more torque, so whilst it was only 3,300hP it did have 222 kN.
Though, apparently, asking on a "drivers day experience" on the East Lancashire Railway "How fast does this go in 1st gear" is not the correct respect for a Napier Deltic BR Class 55 Loco.

[ddom]

Gary C said:

Merc 500SL lost power in the 90's when it lost its overfuel facility. Rather than ensuring complete burn, it needed to overfuel and run a bit rich to get the best BMEP, which resulted in some fuel not being burnt.

So yes, peak power can be delivered 'rich'

I've never seen an engine make more power than when it was slightly lean. Obviously these chancers who tried to flog all manner of kit with headline numbers were all trying it on, but you couldn't compete in them otherwise they would go pop.

[LimSlip]

Equus said:

Well, if you prefer numbers, I suggest you dig a bit deeper: do the calculations on the change of engine speed required to deliver a given change in road speed, and the rotational inertias involved.

Then you will understand the meaning of your 'greater jerk' (!) and the fact that horsepower-for-horsepower, a car with more torque will have considerably more in-gear acceleration than one with less.

"in gear" tests are arbitrary and useless. If you want maximum acceleration you change to a gear that will provide it.