TOT: my car

My petrol car seems to behave like a diesel. I have just gone up a hill in third gear that is too steep to cycle up. Does this suggest unusual gearing ratios? (Or bad driving on my part!)
The car is a Nissan MIcra 1.2 - K12 series.
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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 4000rpm.
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.
--
Chris Green
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On Saturday, 4 August 2018 15:33:05 UTC+1, Chris Green wrote:

at odds with my experiences fwiw
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On 05/08/2018 11:42, snipped-for-privacy@gmail.com wrote:

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 1500RPM, and rev to 7500.
Andy
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On Sunday, 5 August 2018 22:38:34 UTC+1, Vir Campestris wrote:

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
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On 05/08/2018 22:55, snipped-for-privacy@gmail.com wrote:

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
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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.
--
*Ambition is a poor excuse for not having enough sense to be lazy *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Tuesday, 7 August 2018 21:57:20 UTC+1, Vir Campestris wrote:

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
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Not when you are asking it to deliver significant power at below normal idle.
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On Wednesday, 8 August 2018 04:32:37 UTC+1, John Angus wrote:

bzzt 'significant' is too vague to be useful anyway. Power output is invariably limited by vibration at low speeds.
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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.
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On Wednesday, 8 August 2018 06:19:45 UTC+1, John Angus wrote:

about as meaningness

whoosh. You're Rod AICMFP.
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Mind has a habit of stopping below normal idle especially the VW.
--
bert

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On Wednesday, 8 August 2018 16:18:12 UTC+1, bert wrote:

Yes I've noticed ;-)
Yeah so why shouldn't I take the piss outa typo's or brain farts ;)
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On 05/08/18 22:38, Vir Campestris wrote:

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

--
The New Left are the people they warned you about.

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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.
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On 06/08/18 11:26, Scott wrote:

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'
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– Ludwig von Mises
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Chris Green laid this down on his screen :

You are of course WRONG!
Diesel driving involves much less gear changing than the narrow torque curve of a petrol engine. My modern BMW diesel has more than adequate torque even below 1000rpm. cc for cc, a diesel produces more power than petrol. It is usually considered that a 2L modern diesel engine equates to a 3L petrol.
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Absolutely not so.
Like for like, no diesel produces as much peak power (BHP) as petrol. The torque output may be very different, with diesels usually producing more at low revs.
The big difference is most diesels are turbos. Which gives the effect of a larger engine. But it does exactly the same to a petrol engine too.
A state of the art petrol engine with turbo will out perform a state of the art diesel with turbo if both are the same capacity.
--
*I'd kill for a Nobel Peace Prize *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Friday, 10 August 2018 00:37:57 UTC+1, Dave Plowman (News) wrote:

Sure. But diesel power output versus rpm is flatter than petrol. Not that either are anywhere near flat.
NT
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