Red Merle wrote:

PS: Comparing Diesel engines on horsepower is relatively meaningless; even if BMW can squeeze more horsepower out of a 3 litre 6, it’s meaningless without seeing and comparing the torque curves.

I quite agree.

Here are the torque and power curves of the SDV8, the BMW M550D (which has just been superceded), and the Bentley Bentayga.

The tiny little high reving torqueless 3.0 BMW actually beats the SDV8 for torque at very similar rpm. In fact, the two engines are very comparable in torque and power until +3500rpm where the BMW continues to make more power.

The 10% smaller high reving torqueless Audi engine in the Bentley has hugely more torque than the SDV8, and from 1000rpm.

Click image to enlarge

Here's the torque curve of the SDV6 in the sport. Another tiny, high reving torqueless engine.

Click image to enlarge

Bentayga/SQ7 diesel is a generation ahead of anything else, the electric supercharger gives big torque at low rpm.

The older Audi engine in the Cayenne S Diesel shades the SDV8 too.

Those are much more interesting, although the maximum torque figure on the current SDV8 should plateau at 750NM (it used to be 700NM). Is that chart up to date? Can I assume that the X Axis on the SDV8 should be labelled the same as the others?

That Bentley engine is an object lesson in how to do it! Very electric motor like. The slightly narrower plateau, starting 500 rpm higher does give away the low displacement on the BMW a little though.

Comparing the SDV6 (which I used to own) with the SDV8 is an eye opener though

Last edited by Red Merle on 8th Oct 2017 2:12pm. Edited 1 time in total

Alistair wrote:

Fuel economy wasn’t so great at the speed I was towing it on the French motorways though

To be fair though Alistair, that's not the most aerodynamic of boxes to be pulling........  2017 4.4 SDV8 Autobiography
2012 4.4 TDV8 Westminster - Gone, but not forgotten

Trommel wrote:

Bentayga/SQ7 diesel is a generation ahead of anything else

BMEP is really just a way of comparing torque against engine capacity - as it stands the electric supercharged Audi is the most powerful production diesel, it's still fairly economical and has effectively zero lag, the 48V system also runs the electric anti-roll quicker/more efficiently than a hydraulic set up etc. Certainly seems neater than the tri-turbo systems.

Possibly all moot anyway soon, as petrol hybrids seem to the way legislation/sentiment will drive things.

I know what BMEP is Trommel, that's why I used it to compare them.

But it tells the end user very little.

After reading loads of positive reviews i was inclined towards v6 but i strongly suggest to test driving both the v6 and the v8 back to back if possible. After driving the v8 first, i jumped to the v6, within minutes my mind was made up v8 was the one. They were both same age milage condition and on 21'' but v8 felt much more comfortable smoother drive, it felt more luxurious car to me. power wise i was happy with the v6 as well though

Agreed, The V8 also has a different suspension set up and goes far better round corners with less body roll, I found it a far more responsive and relaxed drive. Yes, you can hear the engine ever so slightly more - but then it's a bigger engine with 8 cylinders - I also like to hear the grunt of a V8, why wouldn't anyone and to be fair you can't even hear the engine until you stamp on the throttle. 2021 L405 Vogue SE 4.4 V8 DIESEL ~ #17

One other thing, the V8 comes with the locking rear diff as well