The Lotus Carlton (also called Vauxhall Lotus Carlton, Lotus Omega and Opel Lotus Omega) is a Vauxhall Carlton/Opel Omega A saloon upgraded by Lotus in order to be able to reach speeds up to 285 km/h (177 mph) with acceleration to equal contemporary sports cars. Like all Lotus vehicles, it was given a type designation—Type 104 in this case. The exterior changes were minimal with the addition of a rear spoiler, cooling vents on the bonnet, Lotus badges on the front wings and bootlid, a bodykit and considerably wider wheel arches distinguishing it from a standard Carlton/Omega. The car was only sold in one colour, a shade of green called Imperial Green (similar to British Racing Green).
Performance modifications started with an upgraded engine, which was enhanced by Lotus from the standard Opel 3.0 L (2,969 cc) 24v straight six unit (used in the GSi). The engine was enlarged to a capacity of 3,615 cc (3.6 L). Lotus then added two Garrett T25 turbochargers, which provide up to 0.7 bar (10 psi) of boost from about 1,500 rpm. The original distributor ignition system of the engine was replaced with a three-coil wasted spark system. The distributor drive was re-purposed as a water pump drive for the water-air intercooler circuit. The intercooler itself is manufactured by Behr and is capable of reducing the temperature of the compressed charge from 120 °C (248 °F) to 60 °C (140 °F).
In addition to the aforementioned engine modifications, Lotus directed a number of engineering changes to the engine so that it would perform reliably with the higher power output. To cope with the higher cylinder pressures (about 95 bar (9,500 kPa)), the external webbing on the engine block was reinforced. The crankshaft was replaced as well; early development crankshafts were machined from billet steel in Italy, but the production units were forged by Opel and sent to Maschinenfabrik Alfing Kessler for machining. The cylinder head was left mostly the same as the 4 valves per cylinder from the donor car, although the combustion chamber was milled to reduce the static compression ratio to 8.2:1 (from 10.0:1). The engine was fitted with forged slipper pistons produced by Mahle. Piston connecting rods were replaced with new units made to an original Lotus design.
The same ZF 6-speed manual transmission as fitted to a contemporary Chevrolet Corvette ZR-1 was used to transfer power output to the rear wheels via a rear limited-slip differential shared with the V8 Holden Commodore.
Chassis, brakes, and steering
The multi-link suspension of the Omega, already praised by the automotive press, was modified by Lotus for better high-speed stability and improved handling dynamics. To combat the problem of significant camber change (seen with the car at high speed and when fully laden), the self-leveling suspension from the Opel Senator was fitted. Also borrowed from the Senator was the Servotronic power steering system, which provides full power assist at parking speeds, and reduces the power assist as the road speed increases. The Lotus engineers would have preferred using a rack and pinion steering arrangement, but cost and space constraints limited them to the worm-and-roller arrangement.
Initial sketches for the wheels showed a split-rim composite design, but this was ultimately abandoned in favor of a monoblock wheel design, with cited concerns over the durability of the wheels in poor road conditions. The final design for the 17-inch wheels was manufactured by Ronal, along with wider tyres than those used on the Omega. The Omega is fitted with Goodyear Eagle tyres. The tyre compound used is the same as that on the Esprit Turbo SE, with a combination of oils and low hysteresis. This allows for improved high-speed stability and better performance in wet conditions.
The car is fitted with 12.9 in (328 mm) brake discs with four-piston AP calipers at the front and 11.8 in (300 mm) discs with two-piston calipers at the rear.
Top speed +283 km/h (176 mph)
Acceleration 0-97 km/h (60 mph): 5.1 seconds
0-160 km/h (100 mph) : 11.1 sec.
Peak power output 382 PS (281 kW; 377 hp) at 5,200 rpm
Peak torque 568 N⋅m (419 lb⋅ft) at 4,200 rpm
Displacement 3,615 cc (3.6 L)
Engine type Twin-turbocharged Straight-6
Layout Longitudinal, Front-engine, rear-wheel drive
Transmission Six-speed ZF S6-40 manual
Weight 1,655 kg (3,649 lb)
Production 950 units