Bentley Fires Up Homage to its 4½-Liter ‘Blower’

Bentley’s homage to the iconic supercharged 4½-Liter ‘Blower’ engine has been fired up for the first time at its Crewe plant.

Yet, despite being an “exact” copy of the original motors powering the mighty racing cars of Sir Tim Birkin in the late 1920s, the factory will be hoping the engines will be a lot more reliable than the originals. That’s because despite Blowers playing their part in Bentley history, including helping to secure victory for a naturally-aspirated Bentley Speed Six at Le Mans in 1930, over the 12 races that they were contested, a victory was never secured.

The newly created Blower engines claim to be exact recreations of the original engines including the use of magnesium for the crankcases. The base engine had been designed by WO Bentley himself and like Bentley’s 3-liter before it, the 4½-liter brought together the latest individual engine technologies of the time – a single overhead camshaft, twin-spark ignition, four valves per cylinder and aluminum pistons. The racing version of WO’s 4½-liter engine developed approximately 130bhp, but Bentley Boy Birkin wanted more. WO’s focus was always on reliability and refinement ahead of absolute power, so his solution to finding more power was always to increase engine capacity. Birkin had a different plan – he wanted to supercharge the 4½, an idea that WO thought ‘corrupted’ his design.

With funding from his wealthy financier Dorothy Paget, and the technical skills of Clive Gallop, Birkin commissioned supercharger specialist Amherst Villiers to create a supercharger for the 4½. The Roots-type supercharger, colloquially known as a blower, was fitted ahead of the engine and radiator and driven directly from the crankshaft. Internal modifications to the engine included a new, stronger crankshaft, reinforced connecting rods, and a modified oil system. In racing tune, Birkin’s new supercharged 4½-litre engine was mighty – outputting around 240bhp.

Now Bentley’s modern engineers have entered a program of exhaustive testing in a bid to iron-out the reliability issues with the original power plant. The project is part of the factory’s Blower Continuation Series which is a run of 12 newly-built recreations of one of the most famous Bentleys of all time. Forming the world’s first pre-war continuation series, these 12 cars have all been pre-sold to Bentley collectors and enthusiasts around the world.

With the engineering prototype for the project – Car Zero – now in build, the first engine has been recreated by Bentley Mulliner with the expert support of specialists. While the engine was being built, a team of Bentley engineers began work to prepare one of the four engine development test beds at Bentley’s Crewe headquarters to receive the engine. The engine test facility has been at Bentley since the factory was built in 1938, and the cells were originally used to run-in and power-test Merlin V12 aero engines produced by the factory for the Spitfire and Hurricane fighters of the Second World War.

Preparing the test bed involved making a replica Blower front chassis to hold the engine, which could then be mounted to the computer-controlled engine dynamometer. A new software version to measure and control the engine was written and tested, allowing Bentley’s engineers to monitor and run the engine to precise parameters. As the Blower powertrain is considerably different in size and shape to Bentley’s modern production engines, a number of the original Merlin test bed fixtures, found still in storage at the factory, have been used to adapt the test bed to accommodate these special engines.


With the engine fully installed, first fire-up took place two weeks ago, and the first engine is now proceeding through its defined schedule of run-in before a full power test. The engines will be tested across a 20-hour cycle, gradually increasing both engine speed and load conditions from idle up to 3,500 rpm. Once each engine is fully run-in, a full-load power curve will be measured.

Once test bed running is complete, the next step for Car Zero’s engine will be real world durability. When the build of the car is complete it will start a program of track testing – running for sessions of gradually increasing duration and speed, checking functionality and robustness under ever harder conditions. The test program is designed to achieve the equivalent of 35,000 kilometers (21,747 miles) of real-world driving across 8,000 kilometers (4,970 miles) of track driving and simulates the undertaking of famous rallies such as Peking to Paris and Mille Miglia.

With the use of modern computer models and this exhaustive testing, Bentley’s engineers will be hoping, at last, to prove WO Bentley wrong and that the ‘Blower Bentleys’ can still be fast without being fragile.

— Paul Myles is a seasoned automotive journalist based in London. Follow him on Twitter @Paulmyles_

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