TOT: my car

Petrol engines are generally *more* flexible than diesels. A diesel that produces a torque of x at 2000rpm is not in the slightest any better than a petrol engine that will produce a torque of x/2 at

The petrol engine will likely produce some useful torque at 2000rpm and meybe even less than that, the diesel will likely not produce much at 1000rpm. Thus the petrol engine will require less gear changing than the diesel.

Modern diesels are improving but it still easier to get a petrol engine with a nice flat torque characteristic than a diesel.

Possibly but Nissan make some v good engines thatr pull well low down and have high RPM capabuiltry as well

Get a Daf. Brian

What, the rubber band powered one?

at odds with my experiences fwiw

I've driven various modern(ish) turbo diesels and find they have a narrow power band to add to their turbo lag.

My wife's car and mine are both petrol, and will give usable torque at

Andy

The current diesel can be driven below idle speed even in 4th, picking up speed slowly. I've not had a petrol that does that. If you have to go up to 1500rpm to get anything usable that's way less low end torque.

NT

Are there two types of diesel engine? The old buses had engines that ran very slowly with a lot of torque and a deep sound. New diesels seem to run much faster sometimes with an almost screeching sound.

The ford engine does, I've driven the 2.7V6 fitted to jaguars, and that has been tamed a LOT to give decent torque band but the TD4 firred to MkII freelanders is vile - a ltttle netter than the mindeo engine but still vbery peaky.

It all depends on the turbo. Vraiable geonytery turbos or twin tiurbose can do w huge amount,.

The earlier BMW turbodiesel fitted to MkI Freelanders is excerptionally flat torqiue wise but delivers less power.

That is very true if the engine has variable valve timimg and decent ports and so on

Back in the day it wasn't a great idea to produce an engine that was still producing torque at 7500 because some klutz would then rev it to 8000.

'sports' engines would do that and camne with revcounters to show you when to change up.

fast road cams would imnprove the top end at the expense of low down torque and a lumpy idle

With VVT and rev limiters on many engines now there is no need to engineer in 'rev limiting by loss of torque die to bad breathing'

Nissan and Toyota are pioneers of this sirt of technology.

To summarise: # Turbodiesel performmance is really mostly about turbo design with variable geometry turbos making for a much broader response curve. Some manufacturers dont use it, and it shows with nasty narrow peaky performance. But a well implemented design - the Jaguar Ford V6 will pull from less than 1000 to a red line at 6250.

Petrol performance on normally aspirated enginines is all aboyt breathing and recent advances in variable valve timing as well as of course electronic ignition/fuel injection enable the engine to be optimised over a far wider rev band than used to be the case.

I've driven an old Almera that pulled from around 1200 to 8000rpm. Astonishing engine for a 'shopping trolley'.

Engines get better.

Cars? Not so much

Well in the bad old days you got power out of a diesel by making it BIG and hence it wasn't great at revving. Mechanical fuel injection led to pretty poor and smoky exhausts

The along came the turbo and electronic fuel injection, and various advances in fuel injection like common rail etc etc.

Net result, smaller engine for same power and more revs available and better fuel consumption - and less 'clatter'

What's "below idle" and what's the red line?

Our cars have a good usable range 7500/1500 = 5 fold. And, yes, there is torque below that. But it's not good for the engine, nor is it efficient, so I don't do it.

Andy

Odd. My car is an auto, and spends most of its time in town at around 1000 rpm, with the idle speed being 800. Can't see the maker allowing that if it damaged the engine.

idle speed is 800rpm. Red line I forget, anything from 5k to nearly 6k. Will check if I remember.

On the contrary it's more efficient & better for the engine.

Efficiency: you lose out on valve timing, which is way off at very low revs. But you gain on cylinder fill, which has an even larger gain than valve timing's loss. Driving it like that gets me rather better than mfr mpg figures.

Life expectancy: If you look at engine failure modes, failures are usually much more to do with total number of revs than load. Increasing load & reducing revs makes engines last longer.

NT

Not when you are asking it to deliver significant power at below normal idle.

'significant' is too vague to be useful anyway. Power output is invariably limited by vibration at low speeds.

Not when you are talking about the car being driven that way.

Yes, but that isnt what was being discussed there. Being bad for the engine was.

about as meaningness

whoosh. You're Rod AICMFP.

In article , John Angus writes

Mind has a habit of stopping below normal idle especially the VW.

Yes I've noticed ;-)

Yeah so why shouldn't I take the piss outa typo's or brain farts ;)