Coventry Climax FW Engine

Within the complicated corporate lineage, the reputation of Coventry Climax as the top-rate engine designer/builder is largely credited to Walter Hassan and Harry Mundy, who designed and developed the Feather Weight (FW) together. The following design aspects are credited to these two people, except the last two items, in which Peter Windsor Smith played a considerable role in place of Harry Mundy who left the firm in 1955 and returned in 1963.

• Designed as a fire engine component, one unique requirement the Feather Weight fulfilled was the ability to be run at nearly full throttle without a proper warm-up. This required careful attention to lubrication and thermal expansion rates on its parts, which translated into legendary durability in rough racing environments at a small price of not so frugal oil consumption.

• Another technical significance of the FW series, which was carried over to the FWM, is an interpretation of Sir Harry Ricardo's intake turbulence theory, whereby intake and exhaust valves are tilted to the same side of the engine where intake and exhaust ports are located. In the SOHC reverse-flow cylinderhead design where valves are actuated directly under the camshaft, and where the intake and exhaust ports are located fore and aft of the cylinder bore center, this arrangement allowed intake and exhaust flows to encourage a swirl in the same rotational direction in the combustion chamber going into and coming out of the cylinder.

The FW 38 hp 1020 cc straight-4 SOHC was designed by Walter Hassan and Harry Mundy as the motive unit for a portable service firepump which was supplied to the government under three contracts totaling over 150,000 units. This engine was revolutionary in its lightness, with the bare weight of 180 pounds, combined with the maintenance-free valve adjustment using shims under overhead camshaft.

In 1953 it was adapted for automotive racing as the 1098 cc FWA retaining the cast crank 3 main bearing construction of FW but with distributor ignition in place of magneto, different camshaft and a higher 9.8:1 compression ratio. With a bore of 2.85 inches and a stroke of 2.625 inches it initially produced 71 hp (53 kW) and was first used at Le Mans in 1954 by Kieft Cars. After the FWA was introduced, FW was renamed to FWP (Pump).

The larger bore (3 inches) and longer stroke (3.15 inches) 1460 cc FWB engine followed, it retained the FWA head but had a forged steel crank and produced a nominal 108 bhp (81 kW). The most significant of the series was the FWE which used the FWB bore size and the FWA stroke for a displacement of 1216 cc. In exchange for a 1000 unit purchase agreement signed by Colin Chapman, it was specifically designed with forged steel crank for Lotus Elite but became a firm favourite with a number of sports car racing firms for its racing durability and high power-to-weight ratio.

• FWE Stage I - 10:1 Compression Ratio, Single 1-1/2" SU H4 carburetor on cast iron intake and exhaust manifold, 75 bhp at 6100rpm
• FWE Stage II - Dual 1-1/2" SU H4 carburetors on alloy manifold, standard on Series 2 Elite, 80 bhp at 6100rpm
• FWE Stage III (Super 95) - 10.5:1 Compression Ratio, Dual twin choke Weber 40DCOE, 95 bhp at 7000rpm
• FWE Super 100 - 5 bearing high lift camshaft, steel timing gear, ported head, 100 bhp
• FWE Super 105 - 11:1 Compression Ratio, racing exhaust manifold, 105 bhp

Other FW variants included a short-stroke (1.78 inches) steel crank version of the FWA named the 744 cc FWC, as used by Dan Gurney early in his career in US club racing. The objective of this engine was for Lotus to campaign for the 750 cc Le Mans Index of Performance prize in 1957, three engines were made for this purpose and they successfully won the prize. Lotus also campaigned FWC at Le Mans in 1958.

FWE powered Lotus Elite won their class six times and the 'Index of Thermal Efficiency' once during the 24 Hours of Le Mans. Notably FW series engines in modified forms also powered Lotus Eleven cars which took three class wins at Le Mans and one 'Index of Performance' win.

In 1966-67, Fisher-Pierce of America imported an 85 hp version of FWB with twin-carburetors to be mounted vertically in their outboard marine unit. This boat engine came out to the market as Bearcat 85.

Climax-powered vehicles

Some notable Coventry Climax-powered cars:

• 1911 GWK, 2 cyl. Coventry Simplex
• 1913 Bamford & Martin, 4 cyl. Coventry Simplex, The first Aston Martin
• 1922 Lea Francis C-Type, 1074cc OC
• 1929 AJS Nine, 1018cc OC
• 1930 Crossley 10, 1122cc OC
• 1933 Vale Special, 1098cc OC, 1476cc JM
• 1935 Triumph Gloria, 1087/1232cc OC, 1476/1991cc JM
• 1935 Crossley Regis, 1122cc OC, 1476 cc and 1640cc JM
• 1936 Morgan 4-4, 1122cc OC
• 1954 Kieft-Climax 1100 LeMans, 1098cc FWA
• 1954 Kieft-Climax V8, 2492cc FPE, not raced
• 1955 Cooper T39 Climax 'Bobtail', 1098cc FWA
• 1955-64 Cooper Monaco Mk.I(T49),Mk.II(T57/59),Mk.III(T61/62/64), 1475/1964/2203/2467/2751cc FPF
• 1956/7 Lotus Eleven, 1098cc FWA, 1460cc FWB, 744cc FWC
• 1957 Cooper T43 Climax, 1964cc FPF, The first mid-engine car to win a Grand Prix
• 1957-58 Lotus 12 Climax, 1475/1964/2203cc FPF
• 1957-63 Lotus Elite, 1216cc FWE, 742cc FWMC (UDT Laystall, 1961 Le Mans)
• 1958 TVR Grantura, 1216cc FWE
• 1958-60 Lotus 16 Climax, 1475/1964/2467/2495cc FPF
• 1959 Lotus 17, 1098cc FWA, 1460cc FWB, 742cc FWMA
• 1959 Cooper T51, 2467cc FPF, World Champion
• 1959-65 Turner Sports, 1098cc FWA, 1216cc FWE
• 1960-61 Lotus 18, 2495cc FPF, 1475cc FPF
• 1960 Cooper T53, 2495cc FPF, World Champion
• 1960-63 Lotus 19, 2467/2495/2751cc FPF
• 1961 Cooper T54, 2751cc FPF, The first mid-engine Indy car
• 1962-64 Lotus 23, 742cc FWMC, 748cc FWMB
• 1962-65 Lotus 25, 1496/1497cc FWMV, World Champion
• 1963–76 Hillman Imp, 875 – 998cc derivative of the FWMA, adapted by Rootes
• 1964-65 Brabham BT11, 1497cc FWMV
• 1965 Lotus 33, 1497cc FWMV, World Champion
• 1965–75 Bond 875 and Bond Ranger, low compression version of Imp engine
• 1967-74 Ginetta G15, 875cc Imp and 998cc Rally Imp engines
• 1971-74 Clan Crusader, 875cc Imp engine