In 1921, Pierce slight revised their Model 32 into the Series 33 which would be produced until 1926. It was the ultimate version of Pierce-Arrows huge six-cylinder engine with the ‘Dual-Valve’ cylinder head.
The engine made great use of a twin-spark setup with twin coils, distributors and spark plugs. A switch on the dashboard could turn on either bank of plugs.1
From earlier models, the Series 33 rode on Westinghouse air-spring shock absorbers that relied on a Kellogg air pump driven off the transmission.1
Later refinements to the series included vacuum assisted brakes and a single 14-tower distributor.1