page_title: Coventry Climax
section_title: FWMV
hierarchical_section_title: Coventry Climax / Engines / FWMV
caption_attribution_description: Coventry Climax FWMV 1500cc V8 Formula 1 engine in a Lotus 24
context_page_description: Coventry Climax was a British forklift truck, fire pump, racing, and other speciality engine manufacturer.
context_section_description: The 1.5-litre FWMV V8, developed from FWMC using a crossplane crankshaft, was designed in 1960 and ran for the first time in May 1961.  It produced 174 bhp (130 kW) from 11.5:1 compression ratio and made its debut on Cooper T58 at 1961 German GP in August.  Initial developments resulted in 181 bhp (135 kW) at 8500rpm soon after, but Jack Brabham at Cooper and Stirling Moss at Rob Walker Racing Team suffered over-heating problems while enjoying a great amount of power for the rest of the season.
  The problem was diagnosed to originate in the thermal expansion rate of the cylinder sleeve causing the Cooper Ring in between the block and the head to leak.  With this problem solved in the Mk.II 186 bhp version, having a larger 1.35" intake valves (1.30" previously), FWMV started to score GP victories, ending the 1962 season with 3 wins for Lotus, 1 win for Cooper, 5 second places and 4 third places, in addition to 7 pole positions and 6 fastest laps.
  For 1963, Coventry Climax was able to convince Lucas to supply the cogged belt driven fuel injection system originally developed for BRM with then-unique sliding throttle plates with four round intake bores cut out. With the larger bore (from 63 mm to 68 mm) and shorter stroke (60 mm to 51.5 mm) compared to Mk.II, notable changes include the increase in conrod length (from 4.2" to 5.1" center to center, with a shorter piston crown height) and the switch from crossplane to flatplane crankshaft, which surprisingly did not increase vibration in the higher RPM range because the longer conrod length counteracted the increase in secondary vibration inherent in flatplane design.
  The flatplane crank was adopted partly due to Rob Walker's proposed successor to the 4WD Ferguson P99 Formula 1 having a front engine layout, which could not accommodate exhaust pipes that merge with pipes from exhaust ports on the opposing banks on crossplane arrangement, but this project did not materialise.  Later, such elaborate crossplane exhaust system became known as "bundle of snakes" on Ford GT40, but was a feature of FWMV Mk.I and Mk.II.
  This Mk.III developed 195 bhp (145 kW) at 9500rpm, propelling Jim Clark, Lotus 25 and Team Lotus to 7 wins, 7 pole positions, 6 fastest laps and the World Championship title.
  Mk.4 was developed for 1964 with yet larger bore (72.4 mm) and shorter stroke (45.5 mm) with a larger exhaust valve (from 1.237" to 1.37") and 12:1 compression ratio to result in 200 bhp (149 kW) at 9750rpm.
  One-off Mk.5 was made with larger inlet valve (from 1.35" to 1.40") for 203 bhp (151 kW), which was delivered to Lotus and said to be used by Clark in the 1964 season.  Mk.4 and Mk.5 scored five wins (three by Clark for Lotus, two by Gurney for Brabham), seven pole positions and seven fastest laps.
  A one-off 4 valve Mk.6 had 1.04" intake and 0.935" exhaust valves, new pistons, cylinder sleeves and crankshaft, and had gear driven camshafts as opposed to the previous chain drive.  This engine made 212 bhp (158 kW) at 10300rpm and went to Lotus during 1965.  Another 4 valve one-off, Mk.7, was built with 1.107" intake and 1.043" exhaust and all the new Mk.6 parts for 213 bhp (159 kW) at 10500rpm, and was delivered to Brabham.  However, these engines started showing reliability problems.
  Except for these two one-off 4 valve engines with characteristic ribbed cam covers, all the FWMVs used in 1965 season were 2 valve Mk.5 or earlier versions with various levels of upgrade.  This was because Coventry Climax had started the FWMW flat-16 project, which was finally announced at the beginning of 1965, and had more than a handful in things needed to be developed or solved, so the 4 valve configuration on FWMV did not get completely developed nor did reach a series production.  However, Jim Clark was able to win 6 championship races (3 with Mk.6), 6 pole positions and 6 fastest laps to become the 1965 World Champion.
  At the end of the 1965 season, the failure of FWMW project left Coventry Climax with no 3 litre successor to FWMV for the next season, so a 2 Litre version of FWMV was assembled using Mk.4 bore
caption: FWMV Mk.III on Lotus 24
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