The Lotus Engineering Co., Ltd., will exhibit a Lotus Mk. IX multi-tubultar space-frame complete with Lotus swing-axle independent front suspension, Lotus de Dion rear suspension, outboard front and inboard rear disc-brakes, worm-and-nut steering, and Lotus final-drive unit, and propeller-shaft. A Coventry-Climax EWA 1,100-c.c. single-overhead-camshaft engine — one of several alternative engines which the Mk. IX frame is designed to accommodate — in unit with a proprietary four-speed close-ratio gearbox, will be mounted in the frame, together with all main engine auxiliaries, and Lotus radiator unit. The specification reads as follows: —
Mild steel 18 and 20-gauge round and square-section tubing assembled by acetylene welding. Lower longitudinals are 1 ⅞ in. diameter tubes, upper longitudinals are square-section braced throughout with square and round tubes of appropriate size according to load and function. All engine, gearbox, final-drive suspension, and accessory mountings are welded to the framing. The frame is designed to accept a fully aerodynamic low-drag, two-seater body with a full-length undershield, and twin rear stabilising fins. A forward extension of the frame is arranged to locate the ducted radiotor, while a light-alloy fuel tank, also produced by Lotus, may be accommodated on outriggers on the passenger side of the frame. At the rear, in the tail of the frame, provision is made for battery mounting. Weight of frame, complete with all mounting brackets and body hoops, is 63 lb.
The Mark IX frame is designed for a vehicle with a wheelbase of 7 ft. 3½ in., a front track of 4 ft.0½ in., a rear track of 3 ft. 11½ in. and an overall length of 11 ft. 7½ in. The overall width is 4 ft. 8in., and the height from the ground to the top of the scuttle is 2 ft. 3 in.
Swing-axle pivoting about lower front cross-member, ensuring low roll centre. Fore and aft location by radius-arms, attaching to frame near second main cross-member by Thompson joints. Girling concentric coil-spring and telescopic shock-absorber units provide overall deflection front full bump to full rebound of 6 in.
Burman worm and nut, divided track-rod, attached to bell-crank lever on lower front cross-member. Specially forged steering arms, conventional drag link and drop-arm.
Lotus de Dion rear suspension with Lotus final-drive unit bolted to frame, universally-jointed half-shaft located laterally by transverse Panhard rod, and longitudinally by parallel trailing arms on each side. De Dion tube is of 16-gauge mild steel, diameter 3 in., swept behind final-drive unit. Light alloy housings at each end of tube contain hub and race assemblies. Suspension units as at front, but total deflection is 7 in.
As exhibited, the Mk. IX frame will be equipped with a Coventry-Climax four-cylinder engine and a four-speed gearbox. A special Lotus adaptor unit is used to attach the gearbox to this engine.
The engine has a bore of 72.39 mm, and a stroke of 66.6 mm. The capacity is 1,098 c.c., and the compression ratio 9.75 to 1. Maximum power output exceeds 72 .b.h.p. at 6,000 r.p.m. Single overhead camshaft, operating valves inclined at 20 degrees through inverted tappets. Twin S.U. 1½-in. carburetters.
A Borg and Beck 7½-in. diameter single dry-plate clutch is used in conjunction with the four-speed gearbox. which has synchromesh on second, third and fourth gears.