The block, crank and transmission needed no changes. But the cylinder head was completely new. It had reprofiled ports and water passages, larger inlet valves (1.27 instead of 1.18"), double valve springs, and a high lift camshaft. Not only that, but there was carburation by twin horizontal 1.25" choke Zenith-Stromberg carburettors, a four branch tubular exhaust manifold, and an engine oil cooler mounted behind the engine, close to the rear deck. All these Sports had their engine lids slatted with 'Venetian Blind' to aid oil and water cooling. To deal with the high temperatures, the exhaust valves were made of a very tough alloy: 28/30/4NS The head design was slightly altered to make for better cooling around the valve seats. Carburation was set rich over 4,000 rev. so as not to have a weak mixture at speed -- again to protect the exhaust valves.

In October 1968, with the designation of the Mark 2, the trim of the Sunbeam Imp Sport was downgraded to Super Imp style. Although the instrumentation was more up to date, the ergonomics of the older car were superior.
The name Sunbeam Imp Sport was replaced in April 1970 by Sunbeam Sport. It would gain the same front styling and trim as the Stiletto in September 1970.
Its production would continue until the end of the Imp-era: March 1976. From October 1966 until March 1976 some 10.336 Sports were produced.