2.1 Design analysis  (Page 5/5)

The 2821E gearbox uses a separate bellhousing that is interchangeable between crossflow and Twin Cam engines because they have common bolt patterns. The flywheels and clutches are also interchangeable within the Kent range of engines. However, since the Crossflow power Seven S4 retained the bellhousing for the Twin Cam, it is necessary to fit an additional spacer for the release bearing.

Interior

The interior of the S4 was a great improvement over that of the S3 Seven. In particular it offered more space and allowed taller drivers to fit, although the pedals were still tight. The dashboard was either painted to give a leather grain finish, left in body color or sprayed matt black ( [link] ).

The seats were the same as fitted in the Europa, but without a headrest. They are made of hardboard covered in foam and black vinyl. In contrast to the bare metal finish of the S3 Seven, the S4 had a properly fitted black carpet and a vinyl transmission tunnel cover to match the seats ( [link] ).

The dashboard layout for the S4 included a full range of Smiths gauges ( [link] ), including:

• Speedometer.
• Tachometer.
• Oil pressure.
• Water temperature.
• Ammeter.
• Fuel gauge.

Four rocker switches controlled the lights, heater fan (optional), 2 speed windscreen wiper, and windscreen washer (optional), while the indicator switch and headlight dip switches were located in the “normal” position as storks on the steering column for the first time for a Seven. The horn push was located in the center of the steering wheel. The steering wheel was a 13” alloy spoke wheel (smaller than used in the S3) with PVC rim ( [link] ). The design was the same as used in the contemporary Elan and Europa.

Weather equipment

The weather equipment was one area that the S4 Seven came in for universal praise. While not offering complete drip-free driving (no Seven has ever achieved this), the roof offered reasonable weather protection. As designed by Weathershields of Birmingham the major improvement over previous Sevens was the fitment of sliding Perspex window panels ( [link] ). Another first for a Seven was the option of a stylish hardtop ( [link] ).

Wheels and tires

The S4 Seven was provided standard with 5 ¹ / ₂ " x 13" pressed steel 'bolt-on' rims with chromium plated hub-caps ( [link] ). As an upgrade 5 ¹ / ₂ " x 13" light alloy 'bolt-on' Brand Lotus rims were available at extra cost ( [link] ). Both wheels were supplied with either 165 x 13” Dunlop SP Sport or Goodyear G800 radial tires as standard.

Dimensions

A summary of the dimensions of the Seven S4 is given in [link] .

Performance

[link] summarizes the performance data from contemporary car magazine tests for both the Ford 1600 GT (crossflow) and Lotus Twin Cam powered cars.

Chassis numbering

The initial batches of the Lotus Seven S4 were built by Lotus Components and started with the chassis number S4/2650. Subsequent to the winding down of Lotus Components, the cars were built by the main Lotus Cars factory. Left hand drive cars were given the prefix LBS4 or LS4 . The total number is uncertain since there appears to be a gap in the chassis numbering between 3238 and 3299. Upon transfer of production to Caterham cars thirty seven cars were built; however, Caterham assembled most of these from Lotus leftover cars rather than new manufacturing.

Bibliography

• Lotus Seven Register ( www.lotus7register.co.uk ).
• J. Coulter, Lotus Seven , Amadeus Press (1995).
• A. Morland, Lotus Seven , Osprey Automotive Publishing (1994).
• D. Ortenburger, Legend of the Lotus Seven , Mercian Press (1987).
• C. Rees, The Magnificent 7 , Haynes Publishing (2002).
• W. Taylor, The Lotus Book , Coterrie Press (1998).
• T. Weale, Lotus Seven , Osprey Automotive Publishing, UK (1991).