MERC-AMG GT4’S se­crets

Weight and cost is­sues mean 600bhp four-door model will sit on mod­i­fied C-class and E-class plat­form

Autocar - - THIS WEEK - MATT PRIOR

E-class floor­pan is key

The need to of­fer four­wheel drive is be­hind Mercedes-amg’s de­ci­sion to base its up­com­ing four-door GT4 model on the floor­pan of the lat­est C-class and E-class, rather than its own alu­minium struc­ture.

The pro­duc­tion model, to be re­vealed at the Geneva mo­tor show in March, is visu­ally based on the con­cept GT4 shown at the same event last year. Af­ter the SLS AMG and cur­rent GT, ac­cord­ing to Marc Buttstädt, AMG’S prod­uct man­ager, it is the third AMG to be “100% de­vel­oped by AMG” and he promised “it will be a lot of fun”.

Al­though the alu­minium mono­coque of the ex­ist­ing two-door GT might out­wardly seem suit­able for devel­op­ment into a four-door model (in the way that the As­ton Martin’s VH ar­chi­tec­ture spawned the five­door Rapide hatch­back), it isn’t suited to mak­ing a big saloon.

The prob­lem is that it has a transaxle gear­box. That’s es­sen­tial for giv­ing the GT the slight (53%) rear­ward weight bias it needs to work as a pow­er­ful, rear-drive sports car, ac­cord­ing to AMG’S chas­sis team leader, Markus Hof­bauer. But it rules out be­ing able to of­fer the car with four-wheel drive, which is “es­sen­tial for win­ter driv­ing” and to give the sta­bil­ity ex­pected by saloon car drivers, be­cause tak­ing drive back to the front is com­pli­cated and heavy.

One alternative, Hof­bauer says, would be to give four­wheel-drive ver­sions of the GT4 a hy­brid pow­er­train, with elec­tric power to the front axle – which would also give the po­ten­tial for it to be a part-ev.

Ul­ti­mately, though, cost and weight con­sid­er­a­tions mean that the GT4 – the name of which is likely to change for pro­duc­tion – is be­ing de­vel­oped in­stead on a mod­i­fied ver­sion of the MRA plat­form, which sits be­neath the C-class and E-class.

AMG boss To­bias Mo­ers has pre­vi­ously told Au­to­car that MRA “gives us a floor­pan; it doesn’t limit us”, so it can still choose what­ever di­men­sions it pleases for the GT4. It’s just that its gear­box will be con­nected to the en­gine at the front, where a four-wheeldrive take­off is much eas­ier.

The car will launch as a 4.0-litre, twin-tur­bocharged V8 model with 600bhp, with an 800bhp or so hy­brid model com­ing later.

Hof­bauer told us that he’d pre­fer a driv­e­train with a hy­brid sys­tem that was con­nected to the crank­shaft and ex­isted to in­crease per­for­mance and fill in any torque gaps created by turbo lag, rather than a hy­brid that pro­vided a sep­a­rate elec­tric drive. Tellingly, that’s the type of pow­er­train that was previewed in the GT4 con­cept too.

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