Life on bikes

The very brief history of Turbo motorbikes

Why have production turbo bikes never really taken off? After all, manufacturers have tried just about everything else to squeeze insane amounts of power out of engines. Marc delves into the brief history of Turbo motorbikes, explains the technology and perhaps why it has never achieved its full potential. Does mid-corner turbo lag have anything to do with it..?

Let’s start by going right back to basics and explain What The Frank a turbo is and does.

A four stroke engine has four stages to each cycle. Induction, compression, power and exhaust. Or suck squeeze bang blow.

The engine has to work hard to suck fuel/air mixture in and then just as hard blow out the burnt fumes. That’s energy that could be put to better use, like forward motion.

When a traditional turbo is fitted the exhaust that is blown out goes into one side of the turbo and whizzes the rotor round. On the other side the impeller blows air up a pipe to the induction side of the engine. So the engine gets fuel and air forced into it instead of having to work to suck it in. Also, more mixture gets blown in than would be the case otherwise. More mixture means more power.

This is great in theory but turbos are expensive and the plumbing required is complex. There’s the issue of controlling the speed and heat of the turbo and lubricating it. A turbo needs a wastegate, a valve that opens when the boost gets too high.

Then there’s the problem of lag. When the throttle’s opened the engine spins faster, the increased exhaust spins the turbo faster, the impeller starts pumping air faster and after a while the increased mixture gets to the combustion cylinder. It takes a little while for that to happen and the rider experiences throttle lag followed by a hefty surge of power. Imagine opening it up on a rainy corner, having no response at first and then whoosh! Potential wheelspin and ignominious dismount.

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Then there’s the issue of heat. A device called an intercooler cools the compressed gas mixture before it gets to the combustion chamber, increasing its density and reducing the risk of pre-ignition. Intercoolers add still more weight and complexity.

Turbos spin at insane speeds and the bearings have to have a constant oil supply. One way to destroy a turbo is to hold the engine at maximum revs and then hit the kill switch. The oil pump stops along with the engine but the turbo keeps spinning for a while, sometimes starved of oil. Keep doing that, it won’t last long. Any failure in lubrication will be very bad.

So turbos on bikes are weighty, complex, expensive and laggy. They do provide a performance increase but at a high cost. And adding the word ‘turbo’ to your insurance premium is catastrophic to your bank balance.

There are plenty of custom turbo bikes with different approaches to engineering in a turbo but there have been very few mass produced bikes with a turbo designed in. In fact, I can think of exactly four.

Honda had taken the classic Moto Guzzi engine layout which was ideally suited to air cooling, and inexplicably made it water cooled, heavier, less powerful and added a whole lot of ugly, including a badge with CX500 written on it. These things mysteriously sold in their millions, you still see them about. They were and are massively reliable and long lived. Like cockroaches. My friend Tarquin bought one that had been crashed. It wasn’t any worse than a new one.

In the early ’80s Honda started showing a prototype CX500 Turbo at shows and to a sceptical press.

It was technologically complex, looked, for the time, very futuristic. In fact, you can see the same kind of styling themes on the current much adored Africa Twin. The CX also had fuel injection, digital ignition control, a complex mono-shock suspension and air adjustable forks. Very much the blueprint for most bikes today. It also had the word TURBO spelled backwards on the front of the fairing just so car drivers would know when they saw one of these on their mirror exactly what to expect.

CX500 Turbo motorbike
Image: Flickr user PS Parrot. CX500 Turbo

Comments at the time tended toward the CX Turbo being a Honda pipe dream or a design exercise. V Twin engines have uneven firing pulses, leading to uneven exhaust pressure which is the worst case for a turbocharger that ideally needs a smooth flow of gas, preferably from a multi cylinder engine. That’s possibly the reason Honda picked this model, to show off their skills. But the CX Turbos did end up on the road and in fairly significant numbers.

82 bhp and 47mpg from a 500cc engine is amazing and reports on performance and ride were all pretty positive. It was too large and heavy to be racy and it suffered from turbo-lag. But for long fast trips, it was literally in a class of its own. It wasn’t a cheap bike of course…

The following year CX500Turbo owners were sickened to find Honda bumped the capacity of the model up to 650cc, power up to 100bhp and carried out a range of improvements making it a rather serious bike.

Of course, Honda was showing off. All that new technology crammed into one new model was calculated to get exposure, prestige and inspire consumer aspirations. (You see what I did there, right?)

But Honda didn’t follow through with commitment and the turbos ceased production in 1985. The normally aspirated CX continued with a CX 650 which put out 64 bhp showing how much the turbo actually contributed. It inherited some of the turbo’s good technology and by many accounts was far better than the original plastic pigs. I saw one parked up the other day, faded, battle scarred with over 50000 miles on the clock. You do know what you’re getting with Honda. There’s a whole lot more on the CX500T over on Motorcycle Specs. http://www.motorcyclespecs.co.za/model/Honda/honda_cx500tc_turbo.htm

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Naturally when news of the Big H turbo first leaked the other three Japanese manufacturers shat their pants and started working on their own turbos. All three companies already had really good four cylinder bikes already in production and hastily slapped turbos on them.

Yamaha’s XJ650 Turbo had an ugly ‘futuristic’ makeover which didn’t stop James Bond riding one in Never Say Never Ever Ever Not Never Again. I think KTM might have drawn some inspiration from its looks.  The original XJ650 made a not shabby 71bhp and adding a turbo took it to 90. In most respects, the turbo version is just a standard XJ650 but with some very economical thinking from Yamaha. There’s no watercooling or fuel injection. The suspension was upgraded but the chassis remained the same. Comparative reviews of the time praised Honda’s bold technology but chose the Yamaha as a slightly better real world bike. The model was in production from 1982 to 86 without much in the way of change.

Suzuki’s XN85 featured an odd capacity of 673cc and produced 85bhp. I’m not sure if that’s a downsized 750 motor or an upgraded 550. Manufactured between 1983 and 85 these were the rarest of the turbo generation. Reviews at the time praised the handling but said the engine was uninspiring considering what was in there. Compare that the GSX 750 ESD of the same period which produced 84bhp without the lag, weight, expense and complexity and you see why the model didn’t appeal to consumers or in fact to Suzuki. Concerns were raised in the press about reliability and only a relatively small number were manufactured.

Kawasaki already had three stonkingly good candidates in their GPz 550, 750 and 1100. These engines were the direct descendants of the original Z1 and hadn’t really changed much over the years.

Kawasaki picked the 77bhp 750 to turbocharge in 1983 which boosted its output to an even more stonking 112bhp. Whereas the Yamaha’s turbo unit was cleverly tucked away behind the engine the GPz’s was right in front under the exhausts to make the most of the gasses exiting the cylinders in an effort to reduce the turbo lag. Bit of a risky place to put it though, a relatively straightforward SMIDSY crash into a car turning right into the rider’s path would smash the front wheel into the most expensive single component on the bike. Kawasaki pre-empted this potentiality by extending the GPz’s fairing all the way down and incorporating a metal section over the turbo. I’m not convinced but it looked cool.

GPZ750 Turbo motorbike
Image: Flickr user quirycontinuum. GPZ750 Turbo

The original GPz 1100 had featured fuel injection right from its launch and the Turbo Kwacker got the same treatment. Comparative tests showed the 750 Turbo to be fast and capable of outrunning it’s 1100 big brother. While the Yamaha was a mid capacity bike that had been given a boost the Kawasaki was already a bit of a beast, adding the turbo elevated it to the status of fucking monster. Sadly the Kawasaki only stayed in production for three years.

All four turbo bikes are very different both in the scope of technology and the role they occupied. The Honda and Yamaha are undeniably sports tourers, while the Suzuki and Kawasaki were much sportier. Turbo charging motorbikes was a new and experimental thing and all four companies went about it differently.

So why did they all ‘fail’?

The eighties were boom times in the UK and America, one might think people were looking for something new and exciting. The demand was there.

All four models were re-engineered versions of existing bikes. But that re-engineering wasn’t trivial. All the engines had to have forged pistons to deal with the heat, improved lubrication, tougher cranks and cases, electronics that hadn’t existed previously and a couple used fuel injection. Those are all expensive components compared to the non-turbo models.

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The turbochargers available at the time were the smallest production units ever made and extremely costly. The purchase and insurance price of any turbo bike was extremely high and the advantage of owning one was. Umm. Well. You could legitimately have the word ‘TURBO’ plastered all over your bike. Yes they were faster but the turbo lag made using that power a bit of a challenge. Fuel consumption figures, where available, suggest an improvement but no one buys a sports or a turbo bike with economy in mind. And then there’s the cost of maintenance. I wonder how many replacement turbo units there are in circulation now, or even at the time.

Reading through old reviews and looking at the figures I think the Kawasaki is the only one that lived up to the promise of turning a beast into a monster. But for the same money any punter could just buy the 750’s bigger 1100 brother. I think the real reason they failed is because there was simply no performance or economic advantage to having a turbo.

All these bikes were experiments. Honda’s CX was a technological showcase and the other three were fairly knee jerk responses to it. That makes sense from the company’s point of view. ‘Look what Honda are doing, how are we going to respond?’ ‘Simple, rush out the best turbo bike you can in the time allowed, doesn’t matter if it’s ropey, if the technology takes off we can develop them in more detail later on’ probably sums up the business decision makers at the time. And that’s what they did, and no, turbos didn’t catch on so all those models were quietly discontinued after a very short run.

So is there any future for turbochargers on bikes?

Suzuki seems to think so. I recently attended a focus group to give my impressions on a new model, the Recursion, which features a turbo.

turbo motorbike
Cafe racer styling. Will the turbo give it the performance to match the name?

This bike is very different from all the 80s ones. It’s designed from the outset as a turbo so I’m guessing they’ve only had to design it once armed with the knowledge gathered from the past rather than reengineer an older model. It’s smaller and lighter than the old bikes being a parallel twin somewhere between 600 and 700 cc (I don’t think they’ve decided yet). It’s been designed all in one go instead of taking an older engine and shoehorning in a turbo.

But the role of the bike itself is maybe the most interesting aspect. It looks like a very slim, lightweight cafe racer, sport tourer. Not a supersport built for balls out street racing or to win some kind of pissing contest against the other guys, nor does it look like an economy bike doomed to eternal commuting. It looks more like a bike created for the simple pleasure of riding. I’m still not sure where this model fits in.

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The Recursion’s biggest differences lie in the technology. Unlike the ‘80s bikes the Recursion’s teeny tiny turbocharger will most likely be electronically controlled allowing the manufacturers to give the bike whatever characteristics they want. Maybe even the rider might have some control over engine modes. This is the technology that wasn’t available first time round.

The specs as shown to the focus group were for a light bike with huge amounts of torque and no turbo lag. All of which sounds very tempting. But once the engine is in production other models with different characteristics would be easy to design. Maybe it’s only Stage One of a bigger plan. Perhaps they have bigger and smaller models planned. The big difficulty is getting it over that first hurdle to get it to market.

After getting stung developing models that turned out to be a technological dead end, why are Suzuki keen to go back to this risky territory? All manufacturers have produced new or updated models in response to Euro4 regulations. These are all lighter, more efficient, more powerful bikes than those of the past. The main differences are water cooling and electronically controlled fuel injection, otherwise they’re as conventional as the bikes of the past.

I’m currently drooling over pictures of the (non-turbo) Kawasaki GPz 750 from the 80s. That’s a tasty bike which looks like it could cover serious distance in comfort at high speed. But 531 pounds and 77bhp seems pretty unpalatable compared to the 2012 Z750 R which puts out 106bhp and weighs 456 pounds – you can see how much progress has been made without resorting to exotic turbo technology. So what’s motivating Suzuki? Do they know something that we don’t?

I’m speculating here but, are the other manufacturers also experimenting with new turbos and we just haven’t heard yet, or are Suzuki striking out alone? Is this a response to ever tightening emission regulations? If that’s the case, are turbos the best way forward?

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And what about future technology?

I don’t know how practical or attractive a hybrid engined bike would be to buyers. Although some companies have experimented with them hybrids might never be compact enough for bikes. But there are numerous small companies selling all-electric bikes, none of which I have to say are very tempting yet. But it’s early days. It would only take one of the giant manufacturers to produce one really great electric model at the right price and the other companies would jump in with competition.

Traditionalists who prefer petrol will reject electric bikes but newcomers will see lower running costs from electricity, cheaper simplified maintenance and huge amounts of acceleration and torque. Is that not tempting? When the Honda 750/4 and Kawasaki Z1 first reached this country older riders wiped the oil off their British crankcases and said they’d never catch on because they were too big, complicated, heavy and expensive. Nay sayers now say electric bikes will never be affordable, never have the range and take all night to charge up.

battery technology
Motorola DynaTAC 8000X: Battery technology has come a long way

But look at how battery technology has improved since the eighties. This 1983 bad boy is the Motorola DynaTAC 8000X which had six hours of standby time and 30 minutes of talktime. It also cost £2639. Whiz forward in time to the peak of mobile technology (at least as far as batteries are concerned) and the new Nokia 3310 can stay on standby for a month and talk for 22 hours. No I wouldn’t want to use one either. But, if that’s how far the technology has developed so far then imagine the future.   

Maybe we’re at the start of a transitional period of new technology. We already have electrically powered racing in the form of the TT Zero, I’m sure others will emerge, to develop and publicise the technology. It might only end with all electric bikes but along the way we might see all sorts of technological confectionary. Turbos, hybrids, hydrogen fuel cells, maybe even bikes powered by unicorn tears. Turbocharged ones.

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The Author

Marc Ryan

Marc Ryan

A bike nut since he was 17, Marc was forced to lay off the bikes for over 10 years, on doctor's orders. Finally given the nod he thought he'd ease himself back in gently on an XL 250 but promptly bought an SV650 which made him shit his pants for the first month.
He also writes his own random meanderings at his own blog, https://isontheroad.wordpress.com