III, of which 15,368 units were built (hardtop and convertible) gave way to the Series IIIA in April 1961. Series IIIA In 1961 the Series IIIA was announced with the Series II Sunbeam Alpine engine. Externally and internally the Series IIIA was identical to the Series III. The improvements were directed solely at improving the durability of the car. To this end, engine capacity was increased and a stiffer crankshaft fitted. To increase reliability, the crankshaft incorporated larger diameter connecting rod bearings which called for modifications to the connecting rods and gudgeon pins. Modified oil and water pumps completed the engine changes. As a result, power output increased from to at 5,100 rpm and torque increased from at 3500 rpm to at 3,900 rpm. In addition, the Series IIIA included many detail changes such as an increased diameter front anti-roll bar which greatly improved roadholding, a redesigned clutch bell housing, a revised clutch assembly with nine pressure springs instead of six and a redesigned air cleaner assembly. Inside the car a fresh-air heater, hitherto available only at extra cost, became a standard fitting. All of these changes combined to make the Series IIIA subtly different from its predecessor and to give the Sunbeam Rapier a new lease of life in the showroom. Maximum speed for the Series IIIA was lower than the Series III at . It also took longer than the Series III to get to (19.3 seconds) but its engine was far more durable. In mid 1963, the Series IIIA convertible was discontinued but the hardtop soldiered on until October 1963 when it was replaced by the Series IV. When production of the Series IIIA ceased, 17,354 units had been built. Series IV Late in 1963, Rootes were set to discontinue the Rapier. It was no longer the mainstay of the competitions department because Rootes had directed its motor sport effort towards the Hillman Imp and the Sunbeam Tiger. In fact a totally new Series IV Rapier had been designed, prototypes built and testing completed, and then the Rootes Group changed its focus. The proposed 'Series IV' became the Mark I Humber Sceptre and the old Series IIIA Rapier was redesigned, hopefully to give it a new lease of life as a touring saloon rather than a sports coupé. The most obvious difference was the change to road wheels in common with the rest of Rootes' light car