The Harrison grew to be a large vehicle, eventually having a wheelbase of 10 ft (3.0 m). The 1906 and 1907 models featured a self-starting system which introduced acetylene into the proper cylinder for starting 'on the spark'. The cars came with a four-cylinder engine of 6.3L in capacity, with overhead valves. Pushrods for the exhaust valves had a ring-shaped section so they could straddle the exhaust piping.^[1]