5 Litre V8...... 33.6mpg average!

Skilid · 5 Dec 2011 at 14:52

You can probably switch it off if you didn't want to do it. It is very interesting technology indeed, and much more complicated then it may seem.

mrk · 5 Dec 2011 at 14:54

It's an AMG engine, it's not "not" going to sound like an AMG engine, 4cylinders running or 8.

PMKeates · 5 Dec 2011 at 14:57

EliotG said:
You can probably switch it off if you didn't want to do it.

Of course, but in reality there's no need. Switching to 4 cylinder mode is apparently imperceptible and instant (and I trust that it is), but I just think the whole existence of the 4 cylinder mode in non-economy run mentality is compromised by low output.

Disco Boy · 5 Dec 2011 at 15:35

It strikes me as something that will cost a lot to fix when it breaks...

PMKeates · 5 Dec 2011 at 15:38

Disco Boy said:
It strikes me as something that will cost a lot to fix when it breaks...

It's an AMG Mercedes-Benz; these have cost a lot to fix for a very long time. The invoice for a 500 HP 55 AMG V8 'Hammer' engine alone is in excess of £40,000... before labour.

Cosimo · 5 Dec 2011 at 15:44

mrk said:
It's an AMG engine, it's not "not" going to sound like an AMG engine, 4cylinders running or 8.

Why not?

mrk · 5 Dec 2011 at 15:47

The sound vents and channels the exhaust follows through to the back isn't going to change is it. The bulk of the noise from an AMG is in the exhaust note to begin with.

Just look at any Youtube video of the C63 AMG where the bonnet is up with the engine running, it doesn't exactly sound like a 6.2l V8, but point the mic at the back....

PMKeates · 5 Dec 2011 at 15:54

mrk said:
Just look at any Youtube video of the C63 AMG where the bonnet is up with the engine running, it doesn't exactly sound like a 6.2l V8, but point the mic at the back....

They can use active acoustics to create much of the AMG noise. Bear in mind that as soon as you request more than 40% of the torque, go over 3600 RPM or try to use more than 30% of the power all 8 cylinders will be firing. AMGs are tuned to be reasonably calm under light loads as they aren't out-and-out racing machines, so I suspect this will retain 99% if not 100% of the AMG character by sounding awesome when used but offering just a light rumbly rasp when milling about.

Freefaller · 5 Dec 2011 at 15:56

Jonnycoupe said:
Is it?

The balancer shaft system is the complicated and heavy side of adding it. Turning of 4 cylinder is pretty bread and butter. Honda also did VCM, Variable Cylinder Management.

You still have the extra friction of the cylinders so its not the same as just a 4 pot.

I'm not saying it's more cutting edge or more advanced than batteries - I just don't like hybrids! Gimme a big V8 any day - and one that can be made more ecconomical, even better!

Jonnycoupe · 5 Dec 2011 at 15:58

mrk said:
The sound vents and channels the exhaust follows through to the back isn't going to change is it. The bulk of the noise from an AMG is in the exhaust note to begin with.

A V8 burble is thanks to the frequency of combustion events..... you just halved that going to a 4 cylinder, now from when I checked todays 4 pots can not be made to sound like a V8 by changing the exhaust system.

Cosimo · 5 Dec 2011 at 16:01

mrk said:
The sound vents and channels the exhaust follows through to the back isn't going to change is it. The bulk of the noise from an AMG is in the exhaust note to begin with.

Just look at any Youtube video of the C63 AMG where the bonnet is up with the engine running, it doesn't exactly sound like a 6.2l V8, but point the mic at the back....

Not exactly comparing like with like. It's a newly developed engine and you will always have a different sound with the bonnet up so rather irrelevant.

Interestingly it will have a new sports exhaust system:

For the first time AMG is using a sports exhaust system featuring an exhaust flap on each side. This technology resolves the age-old conflict of an emotional sound during spirited driving and a more discreet engine note at low speed operation.

Each of the two rear silencers has a flap which is variably activated on a logic-controlled basis depending on the driver’s accelerator input and the engine speed. At low loads and engine speeds below 2,000 rpm the flaps remain closed. This causes the exhaust gases to cover a longer distance and flow through an additional damping element, so that the engine sound is pleasantly subdued and irritating frequencies are effectively suppressed. When the driver accelerates, the flaps open at an angle of 15, then 30 and up to 50 degrees so that some of the exhaust gases cover a shorter distance. This produces a sonorous engine note. Under full load at higher engine speeds, in performance-oriented eight-cylinder operation, both flaps are fully opened so that the occupants are able to enjoy the muscular sound typical of an AMG V8.

The twin-pipe AMG sports exhaust system with two chromed twin tailpipes on each side has a diameter of 65 millimeters from the manifolds to the pre-silencer. The diameter is reduced to 60 millimeters from the pre-silencer to the rear silencers.

DRZ · 5 Dec 2011 at 16:04

Jonnycoupe said:
A V8 burble is thanks to the frequency of combustion events..... you just halved that going to a 4 cylinder, now from when I checked todays 4 pots can not be made to sound like a V8 by changing the exhaust system.

There is the fact that the remaining cylinders are still pumping air so whilst there isn't as much air or at the same temperatures, there is still air going down the exhaust pipe from those cylinders.

mrk · 5 Dec 2011 at 16:06

Yes^ that is it! I'd bet 50P that the sound remains unchanged from your typical AMG powered V8.

People were forum-venting all over the web that the current bi-turbo v8 would lose it's AMG "sound" when it was announced and that certainly isn't the case. The same will be for this new engine, AMG won't let that happen either way.

Jonnycoupe · 5 Dec 2011 at 16:07

DRZ said:
There is the fact that the remaining cylinders are still pumping air so whilst there isn't as much air or at the same temperatures, there is still air going down the exhaust pipe from those cylinders.

No they dont.

They valves are closed such that the cylinder acts as an air spring and you mitigate pumping losses. That is the purpose of the 16 actuators described in the article.

Air being pushed out would have no where near the expansion of combused exhaust gases anyway.

Jonnycoupe · 5 Dec 2011 at 16:10

Current V8 AMG sound has already been killed off by the active exhaust system anyway by the sounds of things so being 4 or 8 cylinder sounds like it wont matter. Until you get to those '15degree, 30 or 50 degree' muffler valve angles to allow gasflow to avoid the silencing portion.... it will be on 8 cylinders at that point anyway due to the engine load.