Jack Brabham used his friendship with engineer Phil Irving at Repco. He proposed they design and build a 3L version of the 2.5L engine by using a longer stroke flat-plane crankshaft. The Repco board agreed to his proposal in light of the expected rival 2.75 L Coventry Climax FPF DOHC engine being of four-cylinder configuration deemed to be near-obsolete, and the plan to build the Cosworth DFV (revealed at the end of 1965 by Ford, its sponsor) was not known yet. A small team at Repco under Phil Irving developed the F1 engine, fitted with two valves per cylinder SOHC heads from the 2.5L version. The first advantage of this Repco 620 V8 was its compact size and lightness, which allowed it to be bolted into an existing 1.5-litre Formula One chassis. With no more than , the Repco was by far the least powerful of the new 3-litre engines, but unlike the others it was frugal, light and compact. Also unlike the others, it was reliable and due to low weight and power, the strain on chassis, suspension, brakes, and tyres was low. This engine being based on British/American Rover V8 /Buick 215 block is a common misconception. The Oldsmobile version of this engine, although sharing the same basic architecture, had cylinder heads and angled valve covers designed by Oldsmobile engineers to look like a traditional Olds V8 and was produced on a separate assembly line. Oldsmobile's intention to produce a higher powered, turbo-charged Jetfire version led to significant differences from the Buick 215, primarily in cylinder head design: Buick used a 5-bolt pattern around each cylinder where Oldsmobile used a 6-bolt pattern. The sixth bolt was added to the intake manifold side of the head, one extra bolt for each cylinder, meant to alleviate a head-warping problem on high-compression versions. This meant that Buick heads would fit on Oldsmobile blocks, but not vice versa. Changing the compression ratio on an Oldsmobile 215 required changing the heads, but on a Buick 215, only the pistons, which was less expensive and simpler. GM's later use of parts diagrams drawn for Oldsmobile in Buick parts catalog showing a six-stud cylinder block sowed further confusion. Later Rover versions of the aluminum block and subsequent Buick iron small blocks went to a 4-bolt-per-cylinder pattern. Four world titles for the single-camshaft 16-valve In 1966, the Repco engine was good enough to score three poles