This resulted in the Sprint concept car, at least four of which were produced in July or August; these were a LHD fixed head and LHD drop head, as well as a RHD drop head and RHD fixed head. These cars were all matt black over yellow, with the black line much higher on the flanks than the Elan Sprint gold stripe that duo tone Sprints were liveried. Who thought of the Sprint name is not known. Publicity shots of the car, the left hand drive DHC, show Jochen Rindt at Brands Hatch posing with it before his death at Monza on 5 September 1970. However, these were S4 cars with the paint job and Sprint on the registration plates; underneath mechanically they were pure S4. The resulting publicity sheet confirms this and includes some blurb attributed to Colin Chapman, concerning the design concept of the paint job. The Sprint was announced at the Earls Court Motor Show on 14th October 1970 and the right hand drive DHC and FHC concept cars were on the stand. However, the same publicity sheet as above had the Big Valve engine specifications added to it. Lotus World carried the press announcement, which indicated that the Sprint would be sold with three final drive options, thus justifying the sprint name. It also mentioned the Big Valve engine, of 135bhp, as well as two tone paint finish.
Chapman asked Tony Rudd, the Engineering Director, to design the big valve engine in early October 1970. They felt that an increase in power would pep the car up enough to counter the falling sales. Work on the engine was completed in an amazing ten days. Following development tests, the engine was officially revealed to the press in late January 1971, followed shortly by the Sprint re-launch in February 1971 with the Big Valve engine and duo paint livery. Production of the Sprint and Big Valve engine had already begun in January 1971 at Hethel. The first road test was by Motor, carried in the early March edition of the weekly, indicating probable testing in mid February. This was on an S4 converted to Sprint specification.
From the February re-launch Sprints were officially to have the duo paint livery or optional one colour scheme, semi gloss black wheels with rimbelishers, flat bonnets and the ignition was placed below the steering column, in line with the new European wide safety rules. The Sprint brochure however used an S4/Sprint conversion with silver wheels retained, though a flat bonnet was fitted.