What is supercharging?

In trying to get the fuel into a conventional four-stroke engine, the pistons moving up and down create a vacuum, which in turn provides suction, pulling the fuel through from the carburettor. It’s simple but relatively inefficient.

The function of a supercharger is to push a larger quantity – by weight of petrol-air mixture – to the engine than could be sucked into the combustion chamber through a conventional carburettor arrangement. In effect, it’s a large air pump, similar in function to a turbo, with the only difference being that a turbo must wait for the exhaust gasses to build up, to spool the turbo up, creating turbo lag, whereas a supercharger is direct, coupled to the engine, and its response is directly related to the engine revs. The only downside is that the power to turn the supercharger is power the engine could be sending to the wheel. The power curve continues to rise with the engine speed, far beyond the point at which the normal aspirated engine begins to fall off.

You might also think that using a supercharger to increase power would have negative effect on an engine’s longevity, but the opposite is the case. Apart from increasing the thermal efficiency of the power plant, both cylinders operate with a mixture of equal strength. This even distribution gives a longer life to the engine and prevents local mixture starvation to any one cylinder. The supercharger supplies both cylinders with a surplus of oil that provides upper cylinder lubrication when it is most needed. The way the supercharger’s vanes stir up the fuel/air mixture increases the amount of atomisation. The theory goes that a supercharged engine will use less petrol than a naturally aspirated engine producing the same amount of power. This isn’t the case with the rather thirsty Triton.

With an ordinary engine, the sucking of the less effectively mixed fuel/air has two drawbacks. The suction draws the oil on the cylinder walls into the combustion chamber and it burns away. And when starting such an engine from cold, a choke-type mix which is heavy on fuel will wash the oil already on the bore away, causing more wear. With the supercharger pumping the fuel in, in its highly atomised state, neither of these problems arise.

The clip-ons are off the moped Andy had as a teenager. When he could not find a rear mudguard that fitted the profile of the tyre, he took a front guard and stretched it across its width until it fitted, hence its arc is somewhat tighter.

“The phrase ‘beggars can’t be choosers’ springs to mind,” Andy laughs.

This isn’t Andy’s only motorcycle with a pre-unit Triumph engine. He has seven of them, “one for each day of the week.”

And the power? The supercharger on Andy’s bike produces up to 15psi flat-out. Which is why his 650cc Triumph-engined behemoth has a top speed estimated at 140mph and sounds like the thunder of an approaching cavalry regiment.