MG J-Type supercharged offset single seater

From the outset, Cecil Kimber was determined to prove the sporting prowess of his MGs through competition and embarked on a project to make the large 18/100 Tigress models dominate on the track.

Whilst a team of these was being prepared for the 1930 Double-Twelve at Brooklands, a group of privateers got together to ‘hot up’ a team entry of MG M-Types. Whilst the big 18/100s were busy running their bearings, the little M-Types went on to win the team prize, their sophisticated little OHC engines outlasting and outpacing far bigger machinery. 

There then started a long and rather bitter rivalry between Austin and Morris (through their MG marque). Austin’s little 750 side valves were nearing the end of their development potential but were extremely effective and very reliable. The MGs took some time catching up but eventually overhauled the Longbridge products - forcing Austin to develop the famous Jameson-designed super-sophisticated twin OHC racers.

It wasn’t long before Kimber’s little wonders started to attempt a series of International Class Speed Records. Kimber was determined that an MG should be the first 750cc car to top 100mph – well aware that Austin were shortly to send Malcolm Campbell to Daytona to attempt just such a record. Mad days were spent, with Capt. George Eyston and Earnest Eldridge (both renowned record breakers) tuning reduced capacity M-Type engines with superchargers, and fitting them into a prototype chassis (which was to form the basis for MG chassis design for years to come). Fitted with streamlined coachwork, the car was taken to Montlhery and with a bit of coaxing managed four runs over 100mph, the best being 103.13mph. The deed was done.

Record breaking continued – in 1932 RT Horton took his single seater C-Type ‘Montlhery’ to Brooklands for the 500 mile race in September. The handicap target for 750cc cars was an incredible 96mph, his car winning at 96.29mph over the distance. He had lapped the outer circuit at over 115mph to establish a new Class H record – faster in fact than the Class G figure. By the year end, Eyston had upped the outright speed record for a 750cc to an astonishing 120mph in his highly modified C-Type, whilst MGs took every other remaining Class H record there was to be had.

This then is the background against which this superb 1933 MG J-Type single seater was built, decades later in the early 1990s. The MG Car Club MMM (Midget, Magna and Magnette) Register set an initiative to carry on the record breaking run and this car was built for the job. Originally powered by an ultra-short stroke J-Type engine of just 500cc, it went to Pendine and took a Class I record, before being re-engined to 750cc. It was then taken to Millbrook where it gained a further two long distance Class H records.

Records achieved:

Class I (350cc-500cc). 1 mile standing start. Avg. speed 39.67mph

Class H (501cc-750cc).100 miles standing start. Avg. speed 62.46mph

Class H (501cc-740cc). 2000 km standing start. Avg speed 59.27mph

The chassis itself is standard J-Type  – no. J3400. This was modified to be a replica of the MG factory ‘Magic Midget’ EX127. The back axle was modified with an 8 ½ inch offset and the rear shock absorbers modified to suit. The front axle is standard J-Type, but has torque reaction cables and Morris-based hydraulic brakes with ‘J’ 2 drums. Steering is by a custom-made extended steering column, mounted onto a subframe and fitted with a detachable steering wheel.

A J-Type engine and gearbox are fitted, and to allow for the offset drive, a custom-made involute tooth chain drive was used to offset the driveline to the back axle. The gearbox and chain drive are bolted to the nearside of the chassis. The gearbox itself is a standard J-Type ‘Wolseley’ type twin top box and has a set of close-ratio gears with a first gear ratio of about 2.4:1. An uprated J-Type clutch is used operated by a specially designed pedal set-up to account for its unorthodox location. The diff is a steel nosed PB unit with a ratio of 8/39 (4.875:1), whilst a range of involute toothed gears are supplied with the car so that the new owner can choose from a wide range of overall drive ratios.

The engine is quite something. JB 2302 is fitted with an RACMSA certified and sealed 746cc J4 pattern engine for which the vendor advises us that the MSA Certification papers are available. Based around an original C-Type Chromidium block, which is sleeved back to standard, it houses a fully counterbalanced J4 spec crankshaft (in fact the only EN42B forged MG crank to be made by Phoenix engineering). Corrillo rods are fitted with Cosworth barrel-ground pistons and Honda Racing piston rings and PTFE gudgeon pin pads. The flywheel has been specially lightened and now weighs just 8 ½ lbs. A pattern C-Type engine housing is used with a ‘C/J4’ type water pump. The standard oil pump has been converted to use an external full flow oil filter.

Upstairs, the cam drive is by a lightweight ‘Dummymo’, whilst the head is a custom unit with a unique combustion chamber design to maximise ‘squish’. The compression ratio is around 7.5:1. The camshaft itself is a P-Type circle based shaft with custom built camshaft stands and rocker cover.

Just as they did in period, a supercharger was fitted for the record attempts, in this case a belt driven Marshal/Gregory J75 unit breathing through a 1 3/4 inch SU carburettor with special ‘anti-surge’ bowl. A purpose-built 4-into-1 exhaust exits through a 2 inch pipe via a cherry bomb silencer.

Running on standard petrol, the engine runs at up to 18psi boost and over 70bhp has been seen on the rolling road (before transmission losses). Extensive documentation about its record breaking activities are available, the car having been carefully mothballed for display in the Mouldsworth Museum. It had its rear main bearing replaced recently and the vendor intends to ‘run it up’ prior to the sale.  It currently sits on 15 inch wheels, a fully reconditioned set of 16 inch wheels being included in the sale.

This beautifully finished and prepared low slung single seater has immense potential for running in International, MG Car Club and VSCC events. With a power-to-weight ratio in the region of 200bhp/tonne, and potential for more under methanol power, this unique record breaker, based on correct and period components, is sure to be of huge interest to any MG collector or racer.