Doohan: Four-strokes are the future of 500 GPs

Published: 14 April 2000

IMAGINE the sound this engine would make. Not the muted waspy buzz of a modern 500cc grand prix race engine, but the incredible shriek of a V10 Formula One engine. It’s one of car racing’s biggest attractions, and it’s soon to be heard emanating from bikes at a track near you.

Motors like this will provide the power for the blue riband GP class from 2002 after bike racing’s ruling body last week confirmed four-stroke engines will be allowed into 500s alongside the familiar two-strokes that have won every title since 1975.

Looking at what the rules allow, it’s hard to imagine how the two-strokes will survive, and some say that is the best thing that could happen. Even Mick Doohan, who won all his five world 500 titles on Honda’s legendary NSR500 V4 two-stroke, says it is time for bike racing to grasp the nettle and leave the " old " engines behind, even if that means the death of the world’s most successful race bike – the NSR.

Doohan, who is now Honda’s General Manager of Racing after his retirement through injury last year, said: " This is something I’ve been pushing for over the last few years because we need to open things up and make the sport more technically interesting for manufacturers and fans. No-one is buying two-strokes any more and the bikes out there racing in today’s GPs haven’t really changed much for eight years.

" Bringing in four-strokes also makes the sport more appealing to the engineers, and I’m sure they can make them as fast, or faster, than the current 500s.

" In F1 we’ve seen changes with engine configurations over the years, such as the turbo era, and then a mixture of normally-aspirated V12s, V10s and V8s, and it has been a success. There’s no reason why it wouldn’t work just as well in our sport, and it’s time for a change after more than 20 years of two-stroke domination. "

The new engines will feature unlimited cylinders (down to a minimum of three), with special provisions to allow

oval-pistoned machines which are currently banned. Honda initially made oval-pistoned bikes to overcome rules which said the maximum allowable number of cylinders in 500s was four. By creating these bikes the firm was able to unleash some of the benefits of an eight-cylinder bike.

Its early races were notable for the bike’s lack of success – Freddie Spencer used one, the NR500, at some races during 1981, and though the 22,000rpm motor sounded great, it rarely looked competitive.

But later machines, 750cc bikes racing in the world endurance series, proved both competitive and reliable. They were entered as non-scoring prototypes, and though oval-pistoned bikes were by then banned from competition, Honda continued to develop the concept on the test bench.

These bikes were said by riders to offer a much broader spread of power than similar round-pistoned engines, and though the road-going NR750 unveiled in 1992 was less than a success – it was too heavy and only made around 120bhp – a full-on race engine would make a formidable weapon in the right hands.

But oval pistons could be just one of the new design features which might make it on to the track – and then on to the bikes you can buy. Honda is renowned for trying – and usually succeeding – to be the most innovative manufacturer on the scene, and we know of several other ideas the firm has already tested which it could use from 2002.

Ceramic pistons, for instance. These have been tested in the search for a material whose performance in the right conditions exceeds that of metals.

Even a perfectly machined piston and barrel, made of the highest quality alloys, will expand with the heat generated in a combustion engine.

This expansion – complicated by the fact that the two components will expand at a fractionally different rate – might only be a fraction of a millimetre, but that will still have to be taken into consideration when the engine is built, meaning the piston is not the perfect fit to the bore it could be.

Ceramic parts exhibit virtually no expansion due to heat, so engineers can make the piston a far closer fit to the barrel, which in turn means fewer piston rings have to be used to keep the compression high and there is less power lost by " blow by " , where the exploding fuel-air mixture escapes past the rings. Ceramic is also light.

Plastic is another material much experimented with. Modern plastics, mixed in the right way and with other key elements added, are now so strong and durable they can be used where metal was previously the only suitable material. Even guns have been made with 100 per cent plastic components.

The most successful application in Honda’s tests have been in conrods. Items made of plastic composites have proven to be highly effective.

Lighter than metal items by up to 40 per cent, their only drawback has been questionable reliability with heavier pistons. But since rules say you can have as many cylinders as you want, allied to lighter pistons and the fact that oval pistons need two conrods... well, it can’t be long before plastic internals make their debut.

Other things like carbon-fibre gearboxes have also been tested, which are lighter than metal items and greatly reduce frictional losses, as well as pneumatic and electro-magnetic valves which don’t need camshafts and instead rely on pressurised gas or high voltage to open and close them.

Most of these innovations came from Honda’s involvement in F1 car racing, and its plan to enter its own team and car from 2002 is sending shivers down the spines of the top men at rival factories.

Any involvement in F1 will give Honda a massive head-start in four-stroke engine development.

Critics of the proposed rules claim that they hand Honda a huge technical advantage. They say only Yamaha, which has raced in F1 in the past and is now partly owned by Toyota (which plans to run an F1 team in the future), could hope to match Honda.

But that is not the point. Advocates of the plan have a dream that instead of reducing the number of manufacturers racing, there would be more, with names like Toyota, Mercedes, Ferrari, Renault and even BMW in the fray.

Instead of Suzuki feeling their only option is to spend millions of pounds developing a new four-stroke motor, they could instead join forces with an engine-maker and use its own expertise in chassis development.

Doohan said: " Mercedes-Benz has a successful partnership as an engine supplier to McLaren in Formula One, and there are many other teams doing the same thing with large car companies. Maybe in the future we’ll see motorcycle manufacturers supplying existing GP teams with engines. "

So does this signal the death knell for two-strokes? Well, don’t write them off just yet. They will still be lighter than the four-stroke bikes, and are proven to work. While four-strokes with six oval cylinders might easily make 250bhp, it is doubtful their tyres and suspension would cope unless that technology improves. And that won’t happen overnight. Even now, riders like Jeremy McWilliams have shown that less can be more – his V-twin 500 Aprilia, though up to 50bhp down on V4 rivals, has shown its lighter weight and usability means he can challenge the more powerful bikes.

The trick is not to make awesome amounts of horsepower, but to make it usable. As Doohan said: " Potentially, you could get more than 250bhp with a three-cylinder 990cc four-stroke, which is about 50 more than now, but getting that power on to the ground will still be more important than power figures on a test bench. "

Just don’t forget your earplugs when you go to the British GP in 2002...