The WD9 was the last in the range of the WD series and was introduced late 1961. This engine was basically the same as the WD8 but utilised the later flat type exhaust silencer of the WLB9 and also the Lucas SR magneto. These may have been part of a cost cutting excercise. The WD9 also featured a 'modern' type nameplate rather than the more traditional brass oval as featured on the earlier WD engines. Around 30,000 WD9 units were built during the production run, however they are not often seen on the rallyfield. The WD9 still retained the cast iron finned hopper and was also available in a tank cooled form for longer periods of operation.