Lotus Carlton: the 176 mph four-door

The Lotus Carlton, also called the Vauxhall Lotus Carlton, Lotus Omega and Opel Lotus Omega, is a version of the Vauxhall Carlton and Opel Omega A saloon upgraded by Lotus into a high-performance sports saloon. Like all Lotus vehicles it was given a type number, in this case Type 104.

Lotus Carlton at a glance

Based on one source (English Wikipedia).

History of the Lotus Carlton

The changes began with the engine: Lotus took Opel’s 2,969 cc 24-valve straight-six from the GSi and enlarged it to 3,615 cc, then added two Garrett T25 turbochargers giving up to 0.7 bar of boost from about 2,500 rpm. The distributor ignition was replaced by a three-coil wasted-spark system and the distributor drive was repurposed to drive the water pump for the water-air intercooler, made by Behr, which cut charge temperature from 120 °C to 60 °C.

To cope with cylinder pressures of about 95 bar, Lotus reinforced the external webbing of the block, replaced the crankshaft with a forged unit (production versions forged by Opel and machined by Alfing Kessler), machined the combustion chambers to lower the compression ratio from 10.0:1 to 8.2:1, and fitted Mahle forged slipper pistons and new connecting rods to a Lotus design. Power went to the rear wheels through the same ZF six-speed manual as the Chevrolet Corvette ZR-1, with a limited-slip differential shared with the V8 Holden Commodore.

Outside there were a rear spoiler, bonnet vents, Lotus badges on the front wings and bootlid, a body kit and much wider wheel arches for the 17-inch Ronal wheels on Goodyear Eagle tyres wider than the Omega’s, using the Esprit Turbo SE compound. The car was sold in one colour only, a dark Imperial Green. The rear suspension gained a new arm and revised bushings to change the toe and camber behaviour, the Opel Senator’s self-levelling suspension was fitted, along with its Servotronic power steering; Lotus would have preferred rack-and-pinion but cost and space left the worm-and-roller system. Brakes were 328 mm front and 300 mm rear discs from Portland Engineering with four-piston AP calipers at the front and two-piston at the rear.

The C36GET engine produced 377 hp at 5,200 rpm and 568 N·m at 4,200 rpm, with 470 N·m available from 2,000 rpm. The car reached 60 mph in 5.1 seconds, 100 mph in 11.1 seconds and more than 176 mph flat out, holding the title of the fastest four-door production saloon for many years. Production began in 1990, four years after the Omega went on sale. Opel had hoped for 1,100 cars, but the early-1990s recession and the £48,000 price held sales back and production at Lotus stopped in December 1992 with 950 cars completed — 320 Carltons and 630 Omegas, 150 short of the target. In 1991 Pininfarina showed the Chronos, a coupé concept built to take the Lotus Omega drivetrain on a shortened wheelbase; the only example, without an engine, appeared at the 1991 Detroit Auto Show.

Design and features

• Twin-turbo straight-six: 3.6 litres, 377 hp and 568 N·m.
• ZF six-speed: the same gearbox as the Corvette ZR-1.
• Chassis work: revised rear suspension, self-levelling and Servotronic steering.
• Wide body: flared arches and 17-inch Ronal wheels in Imperial Green only.
• Fastest four-door: over 176 mph, a record it held for years.

Lotus Carlton versions

• Vauxhall Lotus Carlton: the British-market version, 320 built.
• Lotus Omega / Opel Lotus Omega: the continental version, 630 built.
• Pininfarina Chronos (1991): a coupé concept for the same drivetrain, never produced.

The Carlton shared its tyres and engineering spirit with the Lotus Esprit, and its engine work shows the same approach as the later Lotus Elise in lightweight engineering. More cars are in the Lotus collection.

Sources

• Lotus Carlton, English Wikipedia: engine, chassis, performance, production