The handbrake handle type changed from Ford style white insert to Ford style all black, some time in late 1971.
The seats incorporated a device, a simple lip along the edge of the runners, to prevent them tipping forward, as per Federal spec cars.
The steering wheel centre boss became larger, flatter and incorporated a smaller Lotus emblem. This emblem was encircled by firstly a mottled vinyl rim, later a plastic item with radiused lines was used. The steering wheel was covered in a plastic material, not leather. Leather rims had been an option on S4 SEs, though. The steering wheel also had small black covers over the smallest holes, closest to the rim. Early Sprints had S4 steering wheels, which had a more protruding boss of smaller diameter and lacked the small hole covers. Then the new pattern wheels were used but the protruding boss retained, presumably as stock was used up. The final style was in use for all Sprints by December 1971. All had the signature of Colin Chapman etched into the down spoke.
The Lotus twin cam engine power was increased by 20%. The twin cam cylinder head was reworked. In addition to enlarged inlet valves, the compression ratio was increased by skimming the head, the cam shafts were further modified for improved torque and the port shapes were refined.
Weber 40 DCOE 31 carburettors replaced the S4’s Stromberg products. In conjunction with the work carried out on the cylinder head, the jets and chokes fitted to the Weber’s were different to those fitted to previous versions of the twin cam engine. In turn, the Weber carburettors were replaced by Dellorto DHLA 40’s in around May 1972. A service bulletin detailing the changed specifications was issued on 9 June 1972 so Dellortos must have been fitted to Sprints in the factory by May 1972. Dellortos were fitted by Lotus to the Twin Cam Europa from December 1971, so clearly Dellorto was a factory supplier by then. One reason for this change was that Dellorto had been quicker and more willing to change their designs to meet the new European regulations that were due to come in force. They may also have been cheaper than Webers too. Dellorto DHLA 40Es were used on all ECE 15 engines, which were really the same as domestic engines but had different carb jets and ignition settings to meet euro specs. Some of the last Big Valve engines for the domestic market had European specification carbs.
A stiffened, redesigned Big Valve cam cover replaced the earlier engines cover. The Big Valve cam covers, up until August 1972, were always black for UK spec cars. European and Federal cam covers were red. However, some red covers, perhaps on those engines with European specification carbs, were also used on domestic cars, though there seems to be no formula as to whether a UK Sprint had red or black covers after this date. Additionally, the fins on the cam covers and the “LOTUS Big Valve” legend became more sharply defined, with the Lotus font changed, the legend also being read from the cabin end of the car, having initially been read from in front of the car, at some time in mid 1971. Presumably new castings were made, either by a new manufacturer if they were outsourced, or by a change in casting at the factory. Apparently only 50 cam covers were made to be read from the front, perhaps so that it was easier to read when viewing the car at motor shows!
From mid to late 1971 the HT leads were lead up over the cam cover and through the centre of the inlet manifold to the distributor, having always previously been lead under the web cast at the rear of the cylinder head.
The fail safe distributor rotor arm (rev limiter) was modified to be activated at 6750rpm instead of 6500rpm. Late in Sprint production, the distributor type was changed for the Domestic and European markets, from the Lucas 23D4 41189A to the 25D4 41225 model.
The exhaust pipe silencer unit became a straight through single unit, replacing the twin pipes of the S4. The intermediate pipe was also lengthened and a heat shield fitted above the silencer.
A blanking panel was fitted below the radiator to improve air flow. The electric cooling fan motor, brackets and fan were changed during production to a larger motor and four bladed metal fan.
Nearside engine bay heat loss holes were standardised in the Sprint.
Drive shafts had a fail safe device fitted, the purpose of which was to hold the shaft in place if the Roroflex coupling broke. Revised front brake calipers were fitted. The differential mounting was strengthened by inclusion of a brace between the top mounting points.
Strengthened Rotoflex couplings were also introduced. Tony Rudd was reported on his investigation into Rotoflexes in a 1971 Motor Sport article “When I visited Lotus some months ago I spent quite a while discussing the relative merits of Rotoflex couplings and sliding spline and universal joints in the rear drive shafts with Tony Rudd, the firm’s Director of Engineering. Rudd had been dubious of the Rotoflex or doughnut coupling before he joined Lotus and agreed that the diabolical surge they caused had to be cured. To this end various experiments were tried when he joined the firm, one of which was the use of the more conventional u/js. However, for some reason, concerned with the elasticity of the doughnuts, the handling undoubtedly deteriorated considerably using the metal joints. So Rudd did quite a lot of research on Rotoflex couplings and after a couple of improvements has now come up with one that almost entirely eliminates the wind up. These are naturally somewhat more rigid and perhaps, because of this, the ride seems to be a little harder than on the earlier and exceptionally smooth riding Elans.” [Copyright Motor Sport]
The European spec also included a hazard switch and light system, the switch being mounted below the ashtray, between the fan and lamps switches. The instrument bezels were recessed flush with the dashboard.
Federal Sprints retained the Stromberg carburettor setup and included crossover pipes to feed heated air into the inlet manifold. Thus the bonnet bulge was retained on Federal Sprints. These engines also had different timing, compression ratio and cam shafts fitted. As with the domestic Sprints, early Federal Sprints were S4 bodies with Sprint mechanicals; indeed some Federal S4s were changed to Sprint spec by the factory. The majority of the following differences were introduced on Federal S4s (and some on the S3 SS models), but I have no specific data on when exactly. Running lights were fitted to the rear flanks and front set of fenders (bumpers), the sidelight fitting was omitted, leaving a blank in the fibreglass, the hazard warning switch was fitted as well as hazard, handbrake and brake fail lights on the dashboard. The bonnet pull was located on a bracket under the dashboard, below the warning lights. The instrument bezels were recessed flush with the dashboard. The glove compartment door was fitted with a lock. Failsafe headlights with a single vacuum cylinder were fitted, which meant that the headlights rose up if the car was not used after a period of time. Dual circuit brakes were fitted with a larger plastic master cylinder. Hexagonal nuts replaced spinners for the road wheels. The rear lamp cluster had different bulbs and direction lights fitted and operated from a DB10 relay box. The seats had an extended integral headrest in their design. In addition to the VIN plate in the engine compartment, there was a vehicle identity plate fitted at the base of the windscreen, which gave just the unit number, as well as a manufacturers plate located on the inside of the drivers door opening, which gave the month and year of manufacture, as well as the unit number and a Federal emmissions plate on the intake side of the engine compartment.