Engine:
Two race engine types were used with the 1921 Grand Prix chassis depending on event regulations, a 1921 3lt straight eight and a 1916 6cyl 4.9lt:
1921 Indianapolis – 1921 3lt straight eight; four horizontal Claudel Hobson
1921 Grand Prix de l’A.C.F – 1921 3lt straight eight; four Zenith carburetors
1921 Shelsley Walsh Hillclimb – 1921 3lt straight eight.
1922 Isle of Man Tourist Trophy – 1921 3lt straight eight (modified and compression raised); two racing CZC vertical Claudel Hobson carburetors.
1922 Coppa Florio Sicily – 1916 6cyl 4.9lt.
Brooklands – both engine types.
Hillclimbs – both engine types.

The 1921 3lt straight eight :
Credited to Coatalen the design is an Ernest Henry type Straight Eight in-line twin overhead camshaft. Bore and stroke 65x112mm, Capacity 2973cc. Lightweight aluminum alloy cylinder blocks and crankcase. Block cast in two blocks of four; non-detachable head cast in one. Shrunk-in steel liners and screwed- in phosphor-bronze valve seats. Crankshaft of nickel-chrome forging, machined from a single billet; plain bearings. Hollow five main journals and eight crankpins. Each crank throw is counterbalanced. No flywheel. Camshaft driven by train of straight-tooth pinions at the front. Rotation viewed from above anti-clockwise both inlet and exhaust. Pistons are aluminum domed- head carrying three compression rings and an oil groove in the skirt serving instead of scraper ring. Piston clearance 0.015’’ to 0.018’’. Groves 1/16’’. Connecting rods H-section, white metal big end bearings. Four tulip-shape overhead valves (twin inlet and twin outlet) per cylinder (32 in total) inclined at 60 degrees operated by two overhead camshafts through inverted cup-style tappets. Valve clearance (cold) inlet 0.010, exhaust 0.015.Valve timing varies between chassis and in time viz. in 1922 open 12 degrees BBDC close 55 degrees ATDC; 1960 – chassis II: inlet opens 5 degrees BTC and closes 35 degrees ABC. Exhaust opens 45 degrees BBC and closes 10 degrees ATC. Compression 1921 French G.P. was 5.7 to1, increased for the 1922 IoM T.T. to 6.3 to1. Output 112bhp at a maximum 4,700rpm.