Time for a two-stroke comeback

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Cutting carbon emissions and accepting dried-up oil supplies means adopting alternative technology. So, the obvious thing is of course to bring back two-strokes… In a few years Formula 1 racing will introduce new engine regs in an effort to be ‘carbon neutral’. And it could well mean strokers.

“I’m very keen on it being a two-stroke,” said F1’s chief technical officer Pat Symonds. “Much more efficient, great sound from the exhaust and a lot of the problems with the old two-strokes are just not relevant anymore.”

For those of us raised on RDs and TZRs this sounds like fantasy… but it’s not. The tech is ready and waiting. Old two-stroke bikes had bad emissions. They used the crankcases to pump fuel through passageways, with windows (or ports) in the cylinder wall rather than inlet and exhaust valves.

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There was no engine oil for lubrication; instead, oil was mixed to the fuel and got burned in combustion. Poor scavenging could see unburned mixture get into the exhaust, too. Not ideal.

Two-stroke engine cutaway

However, strokers have huge advantages. A four-stroke fires every second time the piston rises (every four strokes) and has to waste energy venting exhaust gas. But two-strokes fire every time the piston rises, so you get the most from the fuel – the most efficient engines are giant marine two-strokes, at over 50% thermal efficiency.

And engineers have solved emission issues. An EU-funded project ran from 1997 to 2001 called ELEVATE – European Low Emission V4 Automotive Two-stroke Engine. They developed direct injection, allowing a four-stroke-style bottom-end and lubrication, with a compressor to scavenge the cylinders.

With flexible ignition and trapping valves (to retain exhaust gas and use it to ignite the next charge), the 2000cc V4 had huge low-rev torque and 90% lower emissions than a comparable four-stroke.

Elevate V4 project

Bolting screw compressors and exhaust valves on a two-stroke compromises its other benefits of being small, light and simple.

But even with these clean-up technologies a two-stroke will still be more compact and weigh less than a comparable four. Which is good news for us: once F1 proves the tech it could lead to bike engines with much greater specific power, less fuel consumption and fewer kilos.

And the F1 rule-makers have another plan to get around the demise of petrol: synthetic fuel. We already use synthetic oil, so why not man-made petrol too?

The days of zinging expansion chambers, home-brewed porting and lightswitch powerbands are unfortunately gone for good. But with ever-tightening emission regulations – and the support of F1 – don’t bet against a phoenix-like two-stroke revival.

Mike Armitage

By Mike Armitage

Deputy Editor, motorcycling.