A Contemporary Take On A Classic — The SOHC Coventry Climax Engine

The majority of the engines employed in motorsports are either purebred designs or highly modified OEM automobile powerplants. There is, however, one notable exception to this rule; the Coventry Climax —which started life as a portable fire pump engine designed for the British government in 1951. Thousands and thousands of the all-aluminum Climax FW (Feather Weight) pump engines were put into service over the years.

However, company president Leonard Lee and his chief engineer, Walter Hassan, saw an opportunity in the automotive world, employing racing as a “halo” for the company. Thus the Coventry Climax FWA (Feather Weight Automotive) powerplant was born. The Climax FWA first appeared at Le Mans in 1954 powering a Kieft Special (Stirling Moss was one of Kieft’s drivers).

With a bore of 2.850 inches and a stroke of 2.625 inches, the 1098cc engine featured a cast crankshaft, three main journals, a compression ratio of 9.8:1, and was rated at only 71 horsepower. It became the mainstay of Colin Chapman’s fabled Lotus Eleven, with a de-stroked version winning the coveted Index of Performance at Le Mans in 1957. A later version of the Coventry Climax (FWB) was enlarged to 1460cc and produced 108 horsepower. Still another (FWE) was used to power the Lotus Elite.

Originally designed as a portable fire pump engine for the British government in 1951, Penta has “rescued” a number of Coventry Climax engines from Europe and stands ready to turn them into racing engines.

Enter Steve Sanett into the picture many decades later. No stranger to racing, Sanett fielded entries to the Indy 500 and Long Beach Grand Prix in the 1980s and decided to try his hand behind the wheel in vintage sports car racing some years later. In 2014 he acquired a Lotus Eleven and has been racing it at SVRA and VARA events — plus the prestigious Rolex Historic Championships at Laguna Seca.

While the car was competitive and won a few races, it simply lacked the power enjoyed by a couple of front-runners in the class. So for 2020, no stone has been left unturned in Sanett’s quest to build the “ultimate” Coventry Climax engine. This would be a “fire pump engine” unlike any other, and endeavor to attain the goal of producing 100-plus horsepower-per-liter with total reliability.

A billet steel crank from Marine Crankshaft replaced the cast OEM unit and beefy steel main caps help support the bottom end by replacing the stock cast aluminum pieces.

Complementing the effort is transplanted Australian engine builder Doug Pearce, now an integral part of the Penta Motorsports team. Moreover, a tremendous amount of intellectual firepower has been focused on Sanett’s Climax by relying on contemporary technology from some of the best aftermarket component manufacturers in the U.S. and U.K.

The 411 on a Pump Designed for 911

The basic FWA block weighs 45 pounds and comes with three cast-aluminum main caps. To strengthen the bottom end, a set of billet-steel caps were sourced from England, but Pearce took things a step further by machining them to accommodate 360-degree thrust bearings from a BMC A-series series motor (Sprite, Mini, Midget) to provide increased support for the billet crank that was manufactured by Marine Crankshaft in Santa Ana, California.

Another important upgrade to the block was the addition of Nikasil to the cylinder liners. The process involves electroplating nickel in the presence of hard particulates, such as Silicon Carbide, under conditions allowing the hard particulate to co-deposit with the nickel. Penta turned to an industry expert, Millennium Technologies of Plymouth, Wisconsin for the process.

The Climax’s four cylinders will be occupied by this combination of Diamond Racing pistons and wrist pins, Pauter rods, and Total Seal rings. The H-beam steel rod, forged aluminum piston, plus wrist pin tipped the scale at a combined 782 grams.

Gliding up and down in the cylinders are specially lightened forged 2618 aluminum pistons from Diamond Racing Pistons, with a dome designed to create a 12.5:1 compression ratio. The slugs are equipped with Total Seal rings — the top rings being of their new gas-ported variety. The connecting rods were manufactured by Pauter Machine of Chula Vista, CA, and weigh 457 grams, while the Diamond pistons were 254 grams, plus 92-gram pins. ACL rod and main bearings were employed to keep everything moving smoothly, reliably.

Enhancing lubrication was another important criterion of the build, with Pearce fabricating a full-length windage tray to replace the half-sized OEM unit. By incorporating a .250-inch-thick 6061-T6 aluminum plate between the block and the pan along with ARP 8740 chromoly pan studs, Pearce was also able to reinforce the bottom end of the motor. The Penta Motorsports crew also fabricated a special oil pump housing that accommodates a taller gear to provide additional oil volume, with an improved pick-up fabricated as well.

A windage tray made of .250-inch-thick aluminum plate controls the oil and also serves to reinforce the bottom end. The oil pump has been enlarged to provide more flow.

Single-Cam Top End

The SOHC aluminum cylinder head has been extensively massaged and the combustion chambers bear more than a passing resemblance to those of an aftermarket SBC head. The intake manifold and port are blended to form a “funnel” that enhances velocity and aims directly at the intake valve. A pair of big Weber DCOE-45 carburetors with 36 mm venturi provide the required air/fuel mixture, while Zig-modified Vertex magneto fires the load.

The valves are 37mm intake and 34mm exhaust with 6mm stems to reduce weight. Special titanium retainers are utilized with individually clearanced lash caps instead of the commonly used cylindrical “biscuits.” The work to the cylinder head was performed by Valley Head Service in Northridge, CA. The valves are actuated by a special camshaft ground to Penta’s specifications by Kent Cams in the U.K. and housed in a durable five-bearing billet machined 6061-T6 support tower. Penta’s Pearce also fabricated an adjustable gear drive to ensure optimum timing accuracy. A Cometic solid copper head gasket, along with other Cometic gaskets for the pan, water pump, and rocker cover provide all of the engine’s sealing.

(Left) Here’s a shot of the Climax’s combustion chamber compared to the chamber of an aftermarket small block Chevy head. (Right) The intake charge is pulled into the engine through a conical intake manifold/cylinder head passage that aims directly at the valve head.

To test the mettle of Penta’s “Pumper,” it was only logical to put the Climax through its paces at Huffaker Engineering in California’s wine country. Joe Huffaker, Sr. (who founded the company in 1966 is a living legend in the sports car community and designed the coveted Huffaker Genie) and his son, Joe Jr. (who has run the company for over 25 years) have built numerous Coventry Climax engines and have everything required to hook the engine up to their late-model SuperFlow dyno.

The initial goal of the project was to have an engine that produced more power than the normal 130-140 horsepower for a full-tilt Coventry Climax engine, while greatly enhancing its reliability — especially in the upper RPM range. From a power standpoint, a maximum of 144.8 horsepower was achieved at 7,200 RPM, with a fairly consistent top-end power curve. As it was just a tick shy of the hoped-for 100-horsepower-per-liter, future dyno sessions are planned to try some other intake system and timing combinations that showed promise.

Penta’s Pearce machined slots into the cam gear to facilitate adjustments. An ARP bolt keeps it snug. Another aftermarket enhancement to the Coventry Climax engine was this CNC-machined cam support.

Now the second part of the equation; reliability. This, of course, will have to be validated by many hours of service on the racetrack. But given the extra attention devoted to improving the bottom-end with big billet main caps, ARP studs, 360-degree thrust bearings, a billet steel crank, and a relatively light rotating assembly, reinforcing the block and fabricating an improved lubrication system —plus lightened valvetrain— having superior durability would seem logical. Time will tell, and the next VARA and SVRA races are just around the corner.

Coventry Climax fans will be interested to know that in the course of their development work the folks at Penta Motorsports have “rescued” a number of FWA and FWB pump engines from Europe and stand ready to convert these into race-ready powerplants for vintage racers. They are available in most any displacement from standard 1098cc and 1460cc configurations plus special sizes. Penta can also refresh existing Coventry Climax engines.

Penta Motorsports engine builder Doug Pearce (left) and Huffaker Engineering’s dyno technician ready the Coventry Climax engine for its workout.

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About the author

Bill Holland

Bill Holland has been involved in racing and the performance aftermarket since the 1960s in the capacities of racer, speed shop proprietor, journalist, street rodder, designer and advertising/PR/marketing professional. Along the way he’s raced Top Fuel and Funny Car, been editor of NHRA’s publication, National Dragster, was involved in off-roading as publisher of SCORE News, built a variety of Featured Vehicles for the SEMA Show, as well as a Track “T” that was a Contender for the AMBR award. He currently races vintage sports cars. Bill was inducted into NHRA’s California Hot Rod Reunion Hall of Fame in 2017.
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