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FWD to RWD Overview

MG’s renowned front wheel drive ZT sports saloon and estate cars were intended, from the outset, to be part of a suite of products which would extend to include extreme sports performance derivatives.  The fundamental strengths of the 75 platform – from which the front wheel drive ZTs are derived – are such that the task of creating executive sports saloons was relatively straight-forward; however it would clearly be unacceptable to transmit very high power through the front wheels only.  The difficult decision was taken to use the basic body structure of ZT, but to completely re-engineer the car under the skin to create a rear-wheel drive performance platform.  The new RWD platform – designed from the outset to meet the demanding requirements of MG Sport and Racing’s forthcoming ZT 385 – also plays host to the lower powered ZT 260, conceived as more affordable, but no less entertaining practical British muscle car.

The FWD ZT’s KV6 engine was tuned to create a classic sports power curve; it’s a gem of an engine that revs sweetly and enthusiastically straight up to it’s red line in a typically European manner.  To set aside the new family of RWD ZT product, the team deliberately chose to start with an engine with quite different power and torque characteristics, matching this to an accomplished sports chassis to create a quite unique product with a very different driving experience indeed to their FWD cousins.

Previously, a project involving a completely different driveline transplant would have been very labour intensive.  However, MG Rover Group had the advantage that the platform was one of the first to have been fully digitised during its design process.  This meant that the installation of alternative power units and transmissions could be achieved rapidly in the virtual environment.  In addition, the decision to retain key elements of the base car’s underfloor geometry, trim and electronics meant that the new platform could be manufactured on many of the same state of the art facilities that produce Rover 75 and ZT, vehicles renowned for their quality and reliability.


A number of potential powerunits were considered before the final decision was taken to employ the proven, robust Ford V8 used to power the infamous Mustang.  Delivering effortless performance, the 4.6-litre powerplant is well proven with over a million units from this engine family produced each year.  MG Rover worked alongside Roush, an established American motorsport and engineering company with a long, successful history of Ford powertrain integration projects (indeed they’re one of the Dream Team businesses working with Ford to deliver the GT40 programme).  Roush used their in-depth knowledge of the engine to develop a calibration which delivered the sharp throttle response demanded by European customers, whilst also achieving the latest European emissions legislation, all within the constraints of the tightly packaged ZT installation.

Tremec’s TR3650 transmission has been adapted from its Mustang application for installation into the ZT 260, whilst the two-piece prop shaft, with constant velocity joints, (similar to that of the BMW M5) is supplied by GKN in Germany.  Dana’s proven Hydratrak® fluid coupling limited slip differential (similar to the unit fitted to Holden’s HSV) was selected for it’s progressive characteristics and wear-free torque transmission system.  Thus the new drivetrain was built up from extremely well proven, ‘bullet-proof’ components.

The vehicle has been tested in a variety of extreme conditions.  Prototypes have been tested through the freezing depths of Swedish and North American winters; they’ve been baked in the searing heat of the central Australian desert.  ZT260s have met the demands of our most exacting drivers on roads as varied as the infamous Nürburgring road circuit to Europe’s highest speed test bowl at Nardo in Southern Italy.

Behind all the work lay the traditional MG credo – ‘Safety Fast’.  The X12 team believes that in the ZT 260 and ZT-T 260 it has produced a range of unique appeal and character: responsive, agile performance machines that are fun to drive, yet effortless mile-eaters – practical British muscle cars.


At the heart of the new ZT 260 is the same robust 4.6-litre V8 engine that serves the American Ford Mustang to such good effect.  From the top down, it has a single overhead camshaft on each bank, which operates two large diameter valves per cylinder.  The engine features sequential multi-point fuel injection, aluminium cylinder heads and a thinwall cast iron block.  The main bearings are cross-bolted, giving an extremely stiff and solid structure (the reserves of strength in this unit are such that it can be supercharged without requiring internal modification and the same block can even be safely used for a 6.7-litre version).  To suit the ZT 260 installation, the normal pressed steel sump is replaced by a special cast-alloy item, which suppresses noise transmission and adds further stiffness to the bottom end.

The engine mounting system is unique, employing twin mass-carrying Hydramounts and a pair of rear mounts to provide a virtual-centre for excellent gearbox control.

Brand new exhaust and intake systems have been developed to comply with stringent European drive-by noise legislation without sacrificing the engine’s torque or power.  In order to meet European emission standards, a bespoke MG catalyst system was created, using a single high-specification catalyst canister for each cylinder bank. These are mounted close to their respective exhaust manifolds for fast light up and efficiency.  The exhaust system is a low-back-pressure design and is manufactured from heavy grade stainless steel throughout.  The design is twinned for almost the complete length of the car; balancing is achieved by employing a short single pipe over the rear axle before splitting again to feed large silencer cans either side of the rear floor.

The result is a 260Ps (191kW) power output and perhaps more importantly, a thumping maximum torque figure of 410Nm (302 lb ft) for real ‘push-in-the-back’ performance in any gear. 

Such torque requires a robust transmission.  The proven Tremec TR3650 five-speed manual gearbox is based on the unit used in the Mustang GT, but with unique ratios specifically chosen to suit the ZT 260 and European driving conditions.  Fifth gear gives a 27% overdrive for effortless cruising at 29.7mph (47.7kph) per 1000rpm engine speed and with so much torque available, fourth gear in the 260 is actually higher than the ZT 190’s fifth.  To match the ZT’s gearchange pattern and ergonomics, MG developed a unique directly mounted remote gearchange mechanism.

Also designed specifically for the ZT 260, MG has developed its own concentric slave cylinder hydraulic clutch actuation system and a unique clutch plate.  As part of the process of integrating the new drivetrain with the inherently refined ZT platform, special attention was paid to NVH control and in particular to the task of balancing good cruising refinement with a rewardingly sporting note when driven hard.  There is an acoustic shroud around the bell housing and tuned sound absorption treatment for the new transmission tunnel.  The two-piece propshaft, with a centre steady bearing and constant velocity joints throughout, is a high performance type with stiff, large diameter tubular construction, similar to that used on the BMW M5.

To get the power down to the road efficiently the final drive unit incorporates Dana’s Hydratrak® limited slip differential.  This uses a cartridge type fluid coupling that apportions torque according to speed differences between the two rear wheels.  If one wheel begins to lose traction and spin, the coupling progressively and smoothly increases torque transfer to the slower-rotating wheel.  The result is enhanced traction, stability and cornering feel.

Latest generation 40mm tubular driveshafts are used to transmit drive to the rear wheels, offering an exceptional combination of stiffness and lightweight.

ZT 260 Body Engineering

There are few production precedents for the kind of driveline transplant involved in the creation of the MG ZT 260 models.  Even Triumph’s evolution from 1300/1500 to Toledo/Dolomite in the 1970s ‘only’ involved a change from front to rear drive, as the engine was already longitudinally mounted.  For ZT 260, the move also included the switch from a transverse to an in-line powerunit installation, an altogether more complex and demanding change.

In order to package the large capacity V8 engine and gearbox, extra clearance was needed in the central bulkhead and tunnel areas.  New pressings and sub assemblies replace the affected sections of the FWD bodyshell, including a deeper centre tunnel extending to the rear of the front seat mounts.

Whilst much of the front subframe structure is carried over from the original hydro-formed component fitted to the FWD ZT, substantial modifications are required to accommodate the new powertrain, it’s mounting system and the new rack location.

In altering the bulkhead configuration, some of the space occupied by the original ZT heating and ventilating system had to be given up.  A new, more compact system, has been developed around a unique, electronically-controlled water-valve heat modulation system.  The ergonomically sound and easy to use temperature and distribution control pack of the FWD cars was deliberately retained to drive the new system.

At the rear of the car, some bodyshell changes were made to accept the new rear suspension and final drive subframe installation.  To optimise weight distribution the main vehicle battery is now located in the boot well below the rear floor, which brings the added benefit of lower battery operating temperatures. 


The FWD ZT’s is highly acclaimed for it’s excellent body control, agility and responsiveness. The X12 team faced the challenge of creating a rear-wheel drive chassis that builds on these core values.  At the front, the MacPherson strut layout of the FWD ZT is retained, though almost all components employed in the ZT 260 application are unique to this car.  The existing forged alloy lower arm is modified and mounted with an all new upright.  The car is supported on Bilstein monotube struts (which offer excellent camber stiffness and a large piston area designed to guarantee fine tuning resolution).  Unique linear rate springs from competition specialists Eibach complete the package.

To accommodate the longitudinal engine configuration, both the steering rack and the uprated anti-roll bar have been re-engineered to sit ahead of the road wheel centreline (rather than behind it).  The steering system boasts a unique steering ratio, whilst the rack itself is driven by a higher capacity power steering pump.  The ZT 260’s steering feel and feedback match the high standards of the original design.

Some of the most fundamental work in the X12 project was that involved in creating the new rear axle installation, which employs a unique 6-mount sub-frame to accommodate the brand new multi-link rear suspension and final drive unit.  New Eibach compound rate rear coil springs react against upper mountings within the subframe, rather than against the standard ZT spring mountings in the underbody.  The lower spring pans are integral within the cast alloy transverse arms that locate the rear ends of the hub carriers; location of the front ends is via a light-alloy trailing arm, with upper and lower steel transverse radius arms.

Bilstein monotube dampers are outrigged behind the hub carriers to maximise damper control through the extra leverage provided.  The rear anti-roll bar is located behind the subframe and mounts to the rear transverse arms.  This intricate rear suspension provides adjustability of camber and toe setting and was developed using advanced modelling techniques to minimise bump steer effects.  It plays a key role in delivering the enjoyable handling, ride and refinement of the ZT 260.

A three-point mounting strategy is employed to locate the differential within the rear frame.  In conjunction with tuned external damping, the system offers excellent control of final drive torque reaction within the frame.

Stopping power is available in abundance from the uprated ZT 260 braking system.  It has ‘H’-split hydraulics and the usual advanced Bosch 5.7 four-channel anti-lock braking, with electronic brake force distribution.

The front brakes are similar to the generously sized (325mm diameter) and proven ventilated discs fitted as standard to the ZT 190, although the sliding pin front callipers are now mounted behind the axle centre-line.  To match the ZT260’s performance potential and revised mass characteristics, the Chassis team worked with brakes specialist AP-Racing to develop new 332mm ventilated discs with an opposed piston alloy calliper design for the rear.

Proven 18-inch diameter, 7.5J rim alloy wheels and 225/45 ZR18 tyres are specified for all ZT 260 models, with the multi-spoke ‘Straights’ design on the 260 and an attractive new ‘Apex’ 10-blade design for the highly-specified 260 SE.  Original equipment tyres are Contisport, chosen through extensive testing as the optimum all-round tyre for stability with responsiveness.


Making the ZT 260

The kind of lateral thinking that led to such an extraordinary low-volume product concept as the ZT 260 was also applied to design the unusual production process on which it is built.  Perhaps the conventional approach to such a project would be to ship the stock car to a specialist engineering company for labour-intensive conversion.  But that would have increased the selling price very substantially, whilst placing at risk MG’s required standards of quality control, value and durability and was hence clearly unacceptable.

After a careful feasibility study and build trials, an ingenious strategy combining regular production processes with dedicated facilities designed to accomplish unique RWD assembly operations was developed.  The bodyshell is built in the conventional way in Longbridge’s highly automated West Works plant.  The only major variation is the new rear floor pressing required to accommodate the rear differential.  A special off-line facility has been installed to complete the transformation into a RWD bodyshell.

With this work completed, the shell re-joins the normal body conveyor to go through extensive main line corrosion protection and paint processes to ensure it can benefit from MG’s comprehensive cosmetic and structural corrosion warranties.

A dedicated ZT 260 parts reception and preparation area has been set up at Longbridge to handle reception and ‘dress’ of the unique powerunit.  Both front and rear subframes are then sub-assembled with their relevant suspension, brakes and powertrain components before being conveyed up to the assembly line.  Their arrival is synchronised with that of the corresponding ZT 260 bodyshell to ensure no disruption the normal high volume manufacturing flow.

Final assembly is completed on the main ZT assembly track, where the ZT 260 is subjected to all the regular stringent quality control procedures of its FWD cousins.