Sunbeam Superchargers
In 1922, in the pursuit of more power from Grand Prix and voiturette racing car engines restricted by prevailing race regulations to 2 or 1 1/2 litres, Fiat developed the supercharger, with satisfactory results, when their cars finished first and second in the 1923 Italian GP. After which the supercharger became the norm in GP racing. Sunbeam, having been the first British make to win the prestigious French GP in 1923 enticed Fiat’s top engineer Bertarione away to their racing and experimental department, and were running supercharged cars from 1924.
These early Sunbeam superchargers have been investigated by Keith Taylor, an STD Register member who owns a 1926 twin-cam 3-litre Sunbeam. As an engineer — he was involved with the new crankcase for Vijay Mallya’s Sunbeam “Tiger” — he was interested in who designed the s/c STD engines and how Sunbeam marine engines fitted into the scheme. For this research he was able to borrow, from John Merryfield, owner of the Sunbeam Tigress, what was thought to be the original single blower used on the V12 4-litre Sunbeam which was the first modern Grand Prix type of car to try for the Land Speed Record raising it to 152.33mph driven by Segrave at Southport sands in 1926. Mr Taylor was able to consult Sunbeam expert Mr Basil Wilding whose father had worked in the Experimental Department at Wolverhampton and was also able to inspect the dual s/c layout used on both the V12 4-litre cars when they went on to perform so successfully at Brooklands and elsewhere. On -Tigress” this layout has been replaced by a large Roots-type supercharger mounted vertically at the front of the engine and driven from the crankshaft by a quill-shaft and bevel gears. Mr Taylor discovered that the supercharger lent to him by Merryfield was not from the LSR car, nor from one of the 1924 2-litre Sunbeam GP cars, but appeared to be from one of the 1 1/2-litre Sunbeam marine engines used in the Duke of York’s Trophy races on the Thames, described some years ago in MOTOR SPORT.
Mr Taylor found that the internal dimensions were smaller than those of the superchargers on the GP cars. Nor did the external appearance line up with that of the GP blower. However, it was remembered that Bertarione had designed engines for the “Invincible” 1 1/2-litre racing Darracqs, and it appears that internal 32.5mm-wide spacer castings had been used to reduce the capacity of the supercharger to suit the smaller engine. Mr Taylor then noted that the positions of the inlet and outlet ports could well be as used for the Sunbeam marine engines. These engines were apparently used in four Saunders of Cowes hydroplane hulls for the aforesaid races and other events, the boats being sold to Woolf Barnato (Ardenrun II), the well-known motor-boat racer Miss Betty Carstairs, Noad Johnston and Malcolm Dangham for £550 apiece.
It appears that these boats were the Henry or Moglia-designed 1921 65x112mm engines with the o h-camshaft drive at the front, whereas the 1923/24 twin-cam 67x105mm Darracq engines had the camshaft drive at the rear. To these older engines it would appear that the 1923/24 Sunbeam Roots superchargers were adapted, with shorter rotors and spacer castings to reduce the length of the rotor chamber from 195mm to 130mm. Apart from dimensions, ii is significant that the rotors were identical to those of the supercharger on the 4-litre Sunbeam. It is thought that synchronising the rotors was done prior to hardening of the gears, as there does not appear to be any means of subsequent adjustment. It is interesting that the blower drive arrangements are similar to the dynamo drive on the 3-litre super sports Sunbeams.
Another change, presumably to render the engines suitable for water-work, was the substitution of the original aluminium cylinder blocks by cast-iron blocks.
I discovered what was apparently one of these Sunbeam marine engines in a junk dealers’ in the 1950s and told Cameron Miller of it. He acquired it for £15 and later it went to went to Neville Webb in Australia. Another of these engines had been obtained by E J Moor, the well-known driver of the GN ”Wasp” at Shelsley Walsh, and had then gone to George Brown around 1946, who proposed to install it in a Triumph chassis. Another motoring association is that David Pearce the nephew of the great Sir Harry Ricardo, bought such an engine in 1936 from a dealer in Pembridge Villas in London, who must surely have been Jack Bartlett, and was told it was the ex-Betty Carstairs engine. It had a professionally fitted multi-plate Bugatti clutch attached to it and had apparently been intended for Billy Cotton’s use. (Could this have been the work of WE “Wilkie” Wilkinson, at Bellevue Garage when the band-leader was looking for something faster than his Bellevue-prepared MG, but who abandoned the idea as he had decided to purchase an ERA?).
Pearce replaced the engine’s gear-type water pump with a centrifugal pump, and, as the magneto was missing found a Delco vertical substitute. This twin-cam, roller-bearing, drysump engine had no starter but was cranked-up through the blower. The former oil/heat exchanger had been replaced by an oil cooler.
Mr Pearce then got hold of a Bugatti chassis from a scrap-heap thought to have been a Type 40, installed the Sunbeam engine, and spent much of his time at Cambridge completing the car and making a rough body for it, when the Engineering Workshops came in handy!
The car was registered but never raced. However, its owner spent 10/(50p) to take it on Brooklands where it accelerated well through the gears and showed a rev-counter equivalent of 115mph, running on Cleveland Discol. But after he had been offered a position as a student-apprentice at the Bristol Aeroplane Company in 1937 he decided that the Bugatti/Sunbeam was not quite the job for commuting, and it was exchanged for a more suitable car with Alan Sinclair who was leaving for Australia with a number of racing cars.
One very interesting point raised by Mr Taylor is that the superchargers for the 2-litre GP cars had the rotor synchronising gears at the front of the blowers, which means that the lower rotor had to incur the whole driving torque. Mr Taylor concedes (as did Laurence Pomeroy in describing the GP Sunbeam in his Grand Prix Car volumes) that no problems appeared to have arisen from this design, but he has found it in no other supercharger he has encountered (so those with s/c engines, please inspect and report if they find GP Sunbeam-style rotor-drive arrangements).
Although the blower lent to Mr Taylor by John Merryfield turned out not to be from the original LSR 4-litre car, he was encouraged to look at the details of how the latter was supercharged. He had been told by Sunbeam expert the late Anthony Heal that the large single blower had rotors that were 230mm long and Mr Taylor deduced from this that their diameter was 128mm. This would match those of the Sunbeam marine engines, the 1934 2-litre GP Sunbeams and the twin blowers which after the record runs replaced the single sic on the Sunbeam “Tiger”, and indeed on the 1926 straight-eight 1 1/2-litre GP Talbots. In fact the LSR had been secured after six of the single blowers had cracked their casings and the seventh had done likewise on the return run, but with the record broken nevertheless. Repairs had been made to this last single unit and it appears that had this not worked Capt Irving would have taken the car back from Southport to Wolverhampton where the twin supercharger installation was ready or at least in hand.
The sic failures due to casing distortion may Mr Taylor thinks, have been due to running the blower at higher than engine speed i e at more than 5300rpm, accentuated when the Sunbeam was airborne and the revs rose even further. Of the later twin-blower installation, as used at Brooklands to take the lap-record, and for road-racing, the superchargers were identical, each with the 128mm diameter rotors and a working chamber with an effective length of 140mm. It is significant that in these the rotor gears were at the drive-end of the blowers, obviating the aforesaid torque stresses on the driving shaft. The ribbing on the casings was slightly modified to simplify casting. All the gears were of case-hardened nickel steel, with straight teeth. It was intended to gear up the blowers, but in the end they were run at engine speed, according to Hears archives. The outboard rotor bearings were lubricated by grease from a hand-gun, the drive gears and inboard bearings from the engine oil system. The offside blower was driven via its inner rotor from the gear driving the nearside blower, with a 46-tooth idler-gear between the other gears. Both blowers naturally rotated in the same direction. The gears ran on ball-and-roller bearings, and the casings were of aluminium. The mixture was fed to the cylinders by a 12-branched log above and between the cylinder banks. That these twin blowers were run at engine speed seems to be proved, because in a box of parts borrowed from John Merryfield. Mr Taylor found two crankshaft gears of 26 and 28 teeth respectively. The former gear would have meshed with one of the same number of teeth to give a direct drive, but a 24-tooth gear would be needed to give a 1.166 speed increase to the superchargers; as it is missing one may assume it was never used? Keith Taylor makes the point that on the GP engine with the sic torque inflicted on the drive-shaft the shafts were not particularly massive, suggesting that the Sunbeam engineers knew about correct material specifications and heat-treatment.
In his investigation into Sunbeam superchargers Mr Taylor recently looked at the Sunbeam “Cub”, which was well-known at Brooklands when Kaye Don raced it, and to the VSCC when driven by Anthony Heal. He noted that although Solex carburettors were favoured by Sunbeam, “The Cub” now has an SU carburettor on what looks like a marine supercharger. At one time Rootes did some work on the car to make it a runner again, and it is just possible that, it the original blower was damaged or lost, it might have been replaced by a marine blower? (Now owned by Peugeot, “The Cub” can be seen in the NMM at Beaulieu).
The twin blower installation was retained on Tiger and Tigress which scored notable successes at Brooklands for Kaye Don (lap record raised to 137.58mph in 1930) and, after the T&T chassis rebuild, for Sir Malcolm Campbell. Tiger remains unchanged in this respect, but Tigress now has the previously mentioned single vertical Roots supercharger.
When Sunbeam built the “Silver Bullet” for the LSR attempt in 1930 its two 24-litre V12 engines were at first boosted with four superchargers on each engine, but for the (abortive) record bid a large centrifugal blower running at 17,000rprn and fed from two Amal carburettors was substituted. In the same year two of the twin-cam three-litre super sports Sunbeams were supercharged for racing, but in this case Gazette vane-type compressors were found acceptable, sucking from Cozette carburettors, giving a 5Ib/sq in boost Mr Taylor has made a very full study of these superchargers, on which this article is based, with appreciation of his co-operation. W B