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More on bike-engined cars

transmissionIn the previous article on this subject, I looked at a reversing differential for a bike-engined car where the engine is mounted longitudinally. Many bike-engined cars are configured with the engine mounted transversely, as it is in the motorcycle from which it is taken. This arrangement is commonly seen in Formula Student, for example.

One particularly enterprising car constructor has developed, and very successfully used, its own gear-drive conversion in place of the existing chain drive. I recently spoke to Del Quigley of DJ Racecars about this transmission and what led him to produce it initially. Quigley explained that he originally used a chain drive on his early Hayabusa-engined cars but that the output of the engine was "destroying chains rather quickly", referring to the 530-section chain.

There is a buoyant market for tuned bike engines in car racing, and the engine specification that was breaking so many chains was producing 220 bhp. The chain run on this chassis, at 220 mm between sprocket centres, was much shorter than in the bike, and this could have been a contributing factor in the shortened life of the chain. Short chains are suspected of having shorter life for a number of reasons, two of which are the shortened time between loads on any given roller, and the smaller angle of chain 'wrap' around the driving sprocket, with fewer teeth consequently carrying the load.

transmission Fig-1-DJ-Firehawk

So the company set about designing and making a bespoke gear drive for its cars, and the first one was run in 2003. DJ Racecars, which is based in Derbyshire, England, manufactures all the machined parts except the gears.

The gear drive is more than capable of handling the torque of the Hayabusa engine, as Quigley explained, "The gear drive came into its own as we have very successfully used it on two supercharged cars, one of which produced 353 bhp at the rear wheels." This output is more than double that of the original Hayabusa engine, for which Suzuki claimed 175 hp before the 2008 model upgrade.

As can be seen from the accompanying photos, the casings are machined from billet aluminium. Although better known for composite chassis and wing manufacture, the company has used its existing CNC machinery to produce some well-machined lightweight casings and other components.

transmission Fig-2-Gear-drive-open

The method by which the gear ratio is changed is by selecting pairs of gears that fit behind an easily accessed cover on the left-hand side of the car. One of these gears fits in place of the original sprocket, while another fits by using interchangeable bearing housings. The hardware for each ratio therefore comprises two gears and two housings, complete with bearings.

In those series that the company is most heavily involved in, hillclimbing and sprinting, there is no requirement for a reversing mechanism. The gear train drives the rear driveshafts via a Quaife differential, often referred to as the 'Radical diff' after the racecar manufacturer of the same name.

Thus far the gear drive has been fitted to five bike-engined cars and has, according to Quigley, been "very reliable".

Fig. 1 - The gear-drive transmission shown installed in a hillclimb chassis (Courtesy of DJ Racecars)

Fig. 2 - This photo shows the gears that are changed in order to vary the drive ratio (Courtesy of DJ Racecars)

Written by Wayne Ward

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