Guide: Mercedes-Benz C111-II
Background
The C111-I first appeared in public at the Frankfurt Motor Show in September 1969, but it wasn’t long before Mercedes-Benz unveiled an uprated version.
The appropriately named C111-II arrived at the Geneva Motor Show in March 1970.
It incorporated a series of modifications that yielded more power, extra torque below 4500rpm, better driver visibility and improved aerodynamics.
Like its predecessor, the C111-II attracted an enormous level of attention.
However, Mercedes were unwavering in their commitment not to produce it for public sale.
Instead, the firm would use the C111-II exclusively for research and development.
The R&D programme was two fold; establish whether Felix Wankel’s rotary engine had a future and experiment with bodyshells manufactured from glass-reinforced-plastic (GRP).
Engine / Gearbox
Whereas the C111-I had a three-rotor Wankel engine mounted transversely in the chassis, the C111-II was equipped with a four-rotor unit.
Each of the piston chambers once again displaced 600cc, which meant overall displacement rose from 1800cc to 2400cc.
Like the three-rotor M950F unit, the new Type M950 KE409 engine ran a 9.3:1 compression ratio with mechanical Bosch fuel-injection.
Whereas some C111-Is had used dual ignition, which proved difficult to adjust, the C111-II was fitted exclusively with single ignition.
Peak power rose from 280bhp to 350bhp at an unchanged 7000rpm. The torque rating was also improved; the C111-II produced 289lb-ft between 4000rpm and 5500rpm compared to 217lb-ft at between 5000rpm and 6000rpm.
Transmission was once again via a five-speed ZF 5DS-25/1 gearbox with triple-plate clutch and limited-slip differential.
Bodywork
Most of the bodywork changes were aimed at achieving a more aerodynamic profile.
The new car was a little longer and fractionally narrower than before.
Much of the additional length came at the front where the nose was extended and given a flatter upper profile.
Auxiliary driving lights were moved to each side of the nose aperture and the indicators were repositioned to each front flank. Previously, these supplementary lights had been located under clear plastic covers on the upper nose element.
To improve cooling, two enlarged vents between the pop-up headlights replaced the rectangular single bank on the C111-I.
To aid driver visibility, a bigger windscreen was installed. This did without the vaned scuttle trim of the 1969 car and ran a single wiper in place of the twin ‘Clap-Hand’ arrangement.
The engine cover was also modified with enlarged sail panel cavities. The engine cooling vents originally housed on the sail panels were relocated to the flat rear deck.
At the back, a tidier rear fascia incorporated circular tail lights in place of the stacked rectangular arrangement seen in 1969.
All told, these modifications resulted in a drag coefficient of 0.325 compared to 0.35 for the C111-I.
Interior
Considerable changes were also made to the interior.
The re-shaped instrument binnacle contained a rev counter and speedometer directly behind the steering wheel. Four supplementary gauges were located off to the right.
The stereo, clock and ventilation controls for the air-conditioning were moved to a vertical console that linked the dash and transmission tunnel.
Upholstery was a mostly leather.
Orange and black checked fabric was used the bucket seat centres and large sections of the door panels.
Chassis
The revised bodyshell was riveted and bonded onto an otherwise unchanged sheet steel monocoque chassis.
Torsion bar suspension was independent all round with double wishbones at the front and an advanced triple wishbone multi-link arrangement at the back.
Anti-squat and anti-dive controls were retained along with vacuum-assisted ventilated disc brakes.
Changes made to the C111-II included a lower ratio for the steering box, modified rear hub carriers with radius rods and ball joints, rubber bag tanks and bigger 15-inch ATS ‘Penta’ five-spoke wheels.
Weight / Performance
Weight rose from 1100kg to 1240kg, but the extra power afforded by the larger engine meant performance was improved.
Top speed was now 186mph (compared to 162mph) and two-tenths of a second was shaved off the 0-62mph time (now 4.8 seconds).
Developments
Over the next few months, several further developments were made.
They included a system that sensed the fuel level in each tank and automatically directed the return flow from the fuel-injection to the tank with the lower fuel level.
One C111-II was equipped with an automatic transmission that used the torque converter and internal gears from a W100 600. It was housed in a special aluminium case sourced from Abarth. Two alternative shift methods were offered: one was fully automatic while the other used motorcycle-type actuation to select gears via a paddle lever.
An advanced anti-lock brake system was developed with Bosch.
Mercedes Abandons the Rotary Engine
The four-rotor Type M950 KE409 was the most advanced of the Wankel engines created at Mercedes-Benz. Many of the engineering problems involved in the rotary-piston principle, especially in engine mechanics, had been solved.
However, the Wankel engine’s poor efficiency owing to the elongated, variable combustion chambers of the rotary-piston principle could not be overcome by technical modification.
Inherent design problems meant a Wankel engine would always require more fuel for the same power output as a conventional reciprocating-piston engine.
Furthermore, with high pollutant content and more stringent emissions legislation on the horizon, Mercedes-Benz chose to discontinue work on rotary engines in 1971.
Production
Seven C111-IIs were built, one of which had a 300bhp M117 V8 engine and modified engine cover.
However, that was not quite the end of the story. The fuel crisis of 1973-1974 saw Mercedes-Benz turn their attention to diesel. As a way to improve the image of the compression-ignition engine, they used a diesel-powered C111-IID as a record setting test bed…
Text copyright: Supercar Nostalgia
Photo copyright: Mercedes-Benz - https://www.mercedes-benz.com
