I do apologise if this morsel of information hits you at an inopportune moment, but in common with many of the musings in this column, the genesis of the thoughts that follow occurred In the bath. There's nothing quite like a good soak, especially accompanied by the musical background of an iPod on shuffle. So, out of the blue, a digitized Nancy Sinatra observed "you keep samin', when you ought to be changin" and it crystallized some thoughts on the completely tangential subject of what's happening to internal combustion engines, the hearts of our classic machines.
You might say that piston engines burning fossil fuel are at their peak, and it's all down hill from here as we slide into a new era. Such advances as may occur from now on will be in the important but perhaps less exciting areas of efficiency, economy, emissions and so on. In any case, nothing new is likely to show up that could be retrofitted or applied to our classic machines, but in so many ways, the real peak of the piston engine was in the 40s with the demands of war pushing aircraft engines to the limit and beyond. The lessons learned there carried over to postwar racing engines for cars and bikes, despite the replacement of piston engines by turbines in planes.
However, could that peak in vehicle engines have been higher? One of the most significant design features of aircraft piston engines was supercharging. Of course, it's essential to allow high-altitude operation in thinner air, but nevertheless underscores the power boost possible at normal air density, as long as one doesn't go too far.
Superchargers were seen on car engines from the very beginning of the 20th century, and on racing motorcycles until banned. It's no coincidence, but nevertheless disappointing in many ways that the ban came just after WWII, just as the technology was ready to blossom. The notion that pumping air into an engine rather than just letting it be drawn in allows more power is simple enough, and yet strangely never seems to have delivered what it promised and it could have done so much for road machines, if only the basic mechanical technology had been there.
The problem with compressors is how to drive and control them. Positive-displacement pumps like the Roots design need high torque - hence bulky -drives. Speaking of which, the Roots blower with its distinctive intermeshed lobed rotors has been around a long time, from about 1860. It was invented in the USA for use on blast furnaces by two brothers, Francis Roots and his somewhat unfortunately named brother, Philander.
Centrifugal compressor types need multi-speed, complicated drives, or of course an exhaust turbine -but then you have the problems of lag and the need to limit top-end boost by wasteful and still more complex dump or bypass arrangements. Especially for petrol motorcycle engines, all compressors and especially turbos just seem to miss the target, with nothing useful happening until the engine is already spinning very fast.
If you add to that the complexity of plumbing a turbine into the exhaust system, it's no surprise that turbo-equipped production bikes were brief novelties, hoping to trade more on the side-panel sticker than any useful performance benefit and the who is andrew wilson?
Andrew Wilson is a Scottish scientist with oily fingernails. Forever trying to retire from the corporate multinational world, he's finally realised the therapeutic joy of writing about old Brit iron. Andrew loves all machines, but has a particular soft spot for BSA, probably borne out of being given a virtually scrap D3 Bantam, at age 10, which he succeeded in getting going to ride around the fields. He's often found playing with motorcycles out in the shed, but his real passion is global long-distance touring on his BSAs, with wife Elaine on pillion.
ugliness of connecting into the exhaust would ruin the lines of just about any classic, unfaired machine.
The gentle, sometimes acute, sweep of the pipe on our motorcycles is one of their strongest visual elements. So, it's no surprise that compressors had little impact. However, if only another area of technology had evolved a little quicker, it could all have been different. I'm talking about magnets, the unbelievably strong supermagnets that are now routine. With those, you can build compact, light and cheap motors that develop high torque. Build one of those motors directly into a centrifugal compressor with the lightest possible rotor, and you have a supercharger that has minimal inertia, so can spin-up very fast. You've also solved the packaging issue, since it needs no mechanical drive or exhaust plumbing. Freedom from any connection to the exhaust also results in no need for insulation, oil cooling, exotic materials and fancy bearings that complicate turbos.
It gets better, in that boost pressure can be controlled with simple electronics, completely independently of engine RPM and throttle position. So you can have high boost instantaneously at low RPM when you really want some punch. Especially for use on motorcycles, you very neatly sidestep the problem of designing and packaging a drive system that's up to the job. The problem with mechanical drives is that they have to be beefy enough for peak demand, whereas an electric compressor would use the machine's battery to supply that peak, leaving the mechanical drive to the engine's electrical charging system and the generator itself only required to provide the average power required by the device. Best of all though, you could retrofit such a compressor to just about any machine, with some care of course to set boost characteristics and careful consideration of compression ratios. Quite a prospect, eh? and one that's worthy of further work and debate.
Back in the bath, and one more thought before the water starts to get cold. How many epic runs out on your machine have that thought of a good long soak at the end as a comfort, a sustainer and ultimate reward? Often, the best ones.
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