Engine conundrum in Gullwing puzzle

Details are coalescing of the car that will replace the Mercedes-Benz McLaren SLR and reprise the spirit of the great 300 SL of 1955. Although originally tipped to surface at this year's Detroit motor show, the new Gullwing will now almost certainly debut in Vision concept form at September's Frankfurt motor show.

In a series of interviews with senior AMG and Mercedes-Benz executives at last week's North American International Motor Show in Detroit, the Carsales Network was able to confirm key details of the car which is tipped to predominately wear AMG, rather than Mercedes-Benz, badging.

The two-place fixed roof car will feature a front mid-engine and adjustable double wishbone independent suspension all round. Brakes will be all-wheel discs, though not ceramic composite as per the McLaren SLR. Forged and machined aluminium componentry will predominate.

Though a coupe (with Gullwing doors obviously), the carbonfibre central structure has been designed as an open car, a la an open-wheel racing car. This is due to the inability of the roof to properly channel crash loads.

As the Gullwing has been designed as a supercar for the road, the car will bolt front and rear aluminium crash structures to the central 'tub'. These 'sacrificial' structures allow Mercedes/AMG to design and 'crash' the car using existing virtual engineering methods.

In practical terms aluminium structures are easily accessed for damage. In contrast a carbonfibre component can 'hide' catastrophic structural damage.

The alloy sub-frames will also mean the car is repairable.

The styling of the car has been completed inhouse and is said to give "a nod" to the original Gullwing, but also point to an "edgier" future for AMG and Mercedes-Benz products overall.

The key fact that seems to have most observers arguing is the configuration of the engine.

What we can tell you is the car's engine code is M268. What we can also tell you is that engine codes are almost sacrosanct in the halls of Sindelfingen and Affalterbach.

What's that mean -- if Gullwing has a new engine code, it almost certainly has a new engine. For example both the 'old' E55 AMG and the McLaren SLR shared the same engine code -- M113. Despite the considerable difference between the engines' power output installation, internal and external componentry, Mercedes and AMG retained the same engine code.

The current 6.2-litre AMG V8 is known as the M156. Insiders say that if the Gullwing was to use a modified version of the stonking naturally aspirated V8 (even if it was turbocharged), it would retain the same M156 designation.

The other issue is packaging. The M156 engine is considerably larger than the M113 as featured in the SLR. With larger cylinder heads and a deeper block the 'big' engine may not fit in the front-mid engine positioning the low and lean Gullwing demands.

So what is M268? The Carsales Network believes the code relates to AMG's own all-new direct-injected engine series -- a forced-induction V-engine of around 5.0 litres.

To be built in long and short stroke versions, the twin-turbo engine will also power the new generation of AMG E, SL and S-Class models. In Gullwing trim, the engine has been pegged at around 430kW and 750Nm.

This torque figures is telling. It appears to correspond with the peak torque loading of AMG's revised seven-speed multiplate-clutch equipped AMG SPEEDSHIFT MCT automatic gearbox.

Alas the number we can't confirm categorically is the cylinder count. The romantics (and marketers) keep hinting at 12, but the engineers and pragmatists favour eight. Given the latter would also yield a stove hot V6 of around 3.0-litres (perfect for future C-AMGs) it's a tempting thought...