AUDI Fined 800 million Euros by German prosecutors, for 6 and 8 cylinder diesels

[DanceswithUnix]

I have noticed that my car can detect that I'm starting to slip the clutch to pull away without bothering to press the loud pedal and gives the engine a few revs for me rather than let it stall. That seems to be beyond the basic anti-stall that engines usually have. So much damned software in these things

[watercooled]

Yeah I also get that, mainly notice it when I'm reversing.

[badass]

Just to understand what you mean - you're saying peak torque when driving is in fact higher than generally shown on dyno, due to e.g. turbo lag? (just for clarification, not disagreeing)

That's the exact opposite to what I'm trying to say Damn text can be a pretty bad media for getting information across!

There are several different types of dyno and they way they arrive at their figures can be fundamentally different. I'm going to focus on one particular type to try to explain where i'm coming from:

This type of dyno holds the revs and measures the power/torque to keep the revs steady. It then allows the revs to rise a bit and then holds again, measuring power/torque. It does this across the rev range.

The end result is that even at say 1200RPM because the revs are held until the output is stable - i.e. the turbo has reached peak boost and the wastegate is opened - the measured power/torque is higher than what you would see in the real world unless you are in a high gear and towing something heavy. In the real world, engine revs rise when floored at and by the time the turbo has hit full boost and teh wastegate is opened, the revs are significantly higher - so peak torque in the real world is both a little lower and later in the rev range.

Lets say it takes the turbo 2 seconds to spool up at ~1500 RPM - in a low gear if you floor it at 1500 RPM, the acceleration of the car means that by the time full boost is hit, the engine is doing 2000RPM. That's above the "peak" torque figure although in reality in a diesel torque is more or less flat from the peak until about 3000RPM so it's not su much about the peak value - it's more about what revs the engine is doing when it reaches that figure.

WRT turbo lag there are two real factors at play causing what is perceived as lag, spooling lag and the low-rpm dip in torque due to backpressure, in turn due to lack of airflow through the engine. Many of the modern small, turbocharged engines have fairly small spooling lag due to small, low-inertia turbos, but also that fairly steep low-down torque curve both due to back-pressure and due to the engine being smaller than an equivalently-powered NA engine, and down that low the turbo won't be doing much to compensate.

In addition, I've noticed in mine, there seems to be some sort of throttle lag, where there's I'd say a few hundred ms delay between moving the throttle and getting any response. Apparently it can be tuned out and isn't present on the performance versions of the same car, so presumably some sort of input smoothing for efficiency?

I suspect that's exactly what that's for. When I floor my death belching diesel at low revs, the "response is instant - it goes straight to max non boosted output with the throttle then the torque slowly builds up to full boost torque over the next 2 seconds or so.

Back to the 3 litre short shifting thing - I don't think there would b any problem with them actually short shifting as you have to select "efficiency mode" every time you start the car. i.e. you would expect the engine to be sluggish to respond so it's not a problem. Save the higher shifting for sporty modes (although sporty and diesel in the same sentence is always a lie)

[watercooled]

I get what you mean now, cheers for the explanation.

[Zak33]

The end result is that even at say 1200RPM because the revs are held until the output is stable - i.e. the turbo has reached peak boost and the wastegate is opened - the measured power/torque is higher than what you would see in the real world unless you are in a high gear and towing something heavy. In the real world, engine revs rise when floored at and by the time the turbo has hit full boost and teh wastegate is opened, the revs are significantly higher - so peak torque in the real world is both a little lower and later in the rev range.

Lets say it takes the turbo 2 seconds to spool up at ~1500 RPM - in a low gear if you floor it at 1500 RPM, the acceleration of the car means that by the time full boost is hit, the engine is doing 2000RPM. That's above the "peak" torque figure although in reality in a diesel torque is more or less flat from the peak until about 3000RPM so it's not su much about the peak value - it's more about what revs the engine is doing when it reaches that figure.

beautifully worded...it's one of the reasons that driving a turbo diesel can be surprisingly rewarding at part throttle and then really shockingly dull under full throttle... every turbo d driver has felt it and almost none of them understand what's going on.

If you drive along in, lets say third gear, at part throttle maintaining engine revs just below peak torque just behind the slow thing you need to over take.. you get a much bigger whoosh when you need it and the gap is there, but the trick on the next gear change is not to change too late but to change so you land on the whoose zone again.

Petrol doesn't suffer it anywhere near as badly as the engine can rev with the boost.

[DanceswithUnix]

Back to the 3 litre short shifting thing - I don't think there would b any problem with them actually short shifting as you have to select "efficiency mode" every time you start the car. i.e. you would expect the engine to be sluggish to respond so it's not a problem. Save the higher shifting for sporty modes (although sporty and diesel in the same sentence is always a lie)

I still don't know where you are getting this short shifting thing from. This is about things like engines requiring more adblue than the engine management actually uses *unless* it detects it is in a lab which it puts far more effort into than you could pass off as accidental. A cringe worthy level of disregard for the regulations.

https://arstechnica.com/cars/2017/05...-new-research/

[directhex]

This is the engine management on a VW:



If the car is between any pair of coloured lines, it gets the NEDC-tested emissions program, which uses the expected levels of AdBlue. If the car moves outside those pairs of lines, the car goes into "alternative" mode which is much higher performance, much higher MPG, but much worse emissions (fails EURO-4)

The white line is the precise parameters of a NEDC run on the dyno.

[badass]

I still don't know where you are getting this short shifting thing from. This is about things like engines requiring more adblue than the engine management actually uses *unless* it detects it is in a lab which it puts far more effort into than you could pass off as accidental. A cringe worthy level of disregard for the regulations.

https://arstechnica.com/cars/2017/05...-new-research/

Briefly, I thought I was going mad, then I found an old Article:

"The affected models were said to pollute between 20 per cent and 100 per cent over the legal limit for nitrogen oxides (NOx) under certain driving conditions. A statement from Audi said the issue lies with the cars' transmission software: "The reason is that in some situations, engine speed is unfavourably influenced by the transmission software, which can have a negative impact on the engine's emissions. "

It's based on a statement from Audi - as in the really trustworthy "we don't lie, nor break the law, nor do we purposefully work around emissions measuring" Audi.

Link: https://www.autoexpress.co.uk/car-ne...vice-discovery

So I stand corrected

I would say they have been taking the peepee but actually its the opposite. They haven't been injecting enough peepee into exhausts to make the cars compliant!

[badass]

beautifully worded...it's one of the reasons that driving a turbo diesel can be surprisingly rewarding at part throttle and then really shockingly dull under full throttle... every turbo d driver has felt it and almost none of them understand what's going on.

If you drive along in, lets say third gear, at part throttle maintaining engine revs just below peak torque just behind the slow thing you need to over take.. you get a much bigger whoosh when you need it and the gap is there, but the trick on the next gear change is not to change too late but to change so you land on the whoose zone again.

Petrol doesn't suffer it anywhere near as badly as the engine can rev with the boost.

I'd never thought of it that way but so true. Loads of part throttle "performance" but when you go full throttle and rev it you get seemingly nothing more.

Also as you say, I haven't had the same disappointment on a modern turbo petrol. Still not as good as a screaming N/A engine but more enjoyable nonetheless.