When I wrote a long piece about the famous blower Bentley single-seater I had seen Sir Henry Birkin racing at Brooklands, which was published in MOTOR SPORT in October 1973, after the late “Rusty” Russ-Turner had let me drive the great car on the road, paced at up to 100mph by his Bentley Corniche, (a previous drive round Silverstone had been frustrated when the cylinder block burst, luckily, for me, when “Rusty” was warming it up) there was one point I could not explain. I raise it now, in the hope that someone, somewhere, may know the answer, or have a few theories.
Birkin hoped to increase the Bentley’s potential by changing its large Villiers-Roots supercharger for a Powerplus vane-type compressor, which protruded beyond the Bentley’s radiator cowl, which the Villiers did not. This may be why Capt G E T Eyston arranged water-heating for the blower, the former 2in S U carburettors being retained. Eyston was promoting Powerplus superchargers, which had been used very successfully on MGs. etc, for racing and record-breaking. Did he persuade Birkin to make the change?” There is no doubt that it was done, the motor papers referring to it and Eyston himself testing the Bentley at Brooklands.
The alteration being judged a failure, Birkin reverted to a modified Villiers supercharger, in conjunction with a bored-out cylinder-block and dry-sump lubrication. This involved huge 62mm downdraught SU carburettors, said to be capable of passing a gallon of fuel every 59 seconds. In this form the Bentley enabled Birkin to raise the lap record to 137.96mph in 1932, just beating that established by Kaye Don in the V12 4-litre supercharged Sunbeam. But was that Powerplus supercharger a failure, or was there some other reason for abandoning it? Amherst Villiers objecting to its use? Eyston needing it for some other experiment? You see, if my records and arithmetic are correct, when it was in use Birkin got within 0.6sec of the Sunbeam record (137.58mph), and the car accelerated well. Indeed, in this form the Bentley lapped in two races only 0.8sec slower than Birkin’s 1932 lap-record on a clear track and, according to Birkin, he had lapped in practice at the equal of the Sunbeam’s record he then wanted to beat, with the Bentley in Powerplus form. Certainly the car caught fire and gave Sir Henry some difficult moments. But such a brave driver would hardly have discarded the new blower on that account, and anyway it was an auxiliary fuel-tank which caught fire. When Dr Benjafield drove it in the 1931 500-mile race, the Bentley retired, with, it was said, a stretched valve — surely not the fault of the supercharger? Eyston, not used to the Bentley, had lapped in it at over 134mph while his Powerplus installation was only just being tested. Surely it could not have been seen as adverse publicity for the production blower-4 1/2 cars to use a different make of supercharger on one highly-developed racing car? So does anyone know what the answer was? W B