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Forced Air Induction : More Power To Burn

Looking back at the path to more power through a variety of forced air induction techniques.

Trying to add more oxygen to the air/fuel mixture has been the objective for as long as internal combustion engines have been rolling down the road. More fuel and more oxygen equal more power. Larger displacement, higher compression ratios, more valves and more sparkplugs also lead to more power but those options are limited. The engine can only be so big allowing only so much room for valves and plugs. There is also a limit to compression. But forcing more air into an engine appears an almost boundless and a straightforward proposition if you can gather and move that air.

In this issue Bertrand Gahel finally has the opportunity to ride the Kawasaki H2 though not the truly fire-breathing H2R (Read, “After the Hype”). He was impressed but left with a feeling that while the H2—and particularly the H2R—are stunning examples of engineering and technical skill brought to bear by the many arms of Kawasaki Heavy Industries, the H2 as a whole might be challenged to equal the sum of its amazingly complicated parts and its power output. 

Building a better, faster more impressive motorcycle has long relied on the ability to get more power from the engine: 200 horsepower now being the new 160 hp. Never before in the realm of motorcycles have there been so many production motorcycles producing such stunning power to weight ratios. The H2R stands at the pinnacle of that performance bar.  

The major development of the H2 is its supercharger and in its supersonic blur of spinning turbine blades the ability to introduce more air to the combustion chamber. 

There have been a great number of other efforts to provide more air to the fire over the years and Kawasaki was already using supercharging it in its PWC line. Of the others, the most obvious are the gaping intakes, which are static devices that produce a ram air effect by gathering clean, cooler air at a high pressure point and funneling it to an airbox, condensing it and feeding it to the fire. You can see these intakes on just about every high performance bike on the market. 

The most prominent may have been on the old Kawasaki ZX-12R where the funnel intake protruded from the fairing of the bike like an errant proboscis. However, ungainly didn’t mean squat when the condensed air intake helped the ZX-12 produce prodigious amounts of torque and horsepower and allowed the big Ninja to confidently face the mighty Suzuki Hayabusa on a relatively level playing field. 

Forced Air Induction – With a Little Extra Push

Static is good (and simple) but an active system or forced air induction device that gathers air and forces it through the system is more effective. Two ways of doing this are supercharging or turbocharging. Both systems have the same goal but they come at it differently. The turbo works off exhaust gases that spin a turbine to feed air to the motor. The higher the engine load the more boost. Turbochargers in motorcycles had their heyday in the early 1980s. 

Kawasaki, Honda, Suzuki and Yamaha all offered turbocharged motorcycles: Honda CX500 Turbo, Yamaha Seca Turbo, Kawasaki GPz750 and Suzuki XN85. 

It is difficult to look at these four and see a comprehensive plan or objective for the turbocharged motorcycles. Two were decidedly non-sporty in execution. The Honda was an opposed twin with a shaft drive but it was high tech for the time with features like four valves per cylinder, fuel infection and, importantly for this application, liquid cooling. As Honda is apt to do even now, they were going to use the best available platform to engineer the best available product. That a rather pedestrian bike with a small displacement and a wet weight approaching 272 kilograms fit the bill was an afterthought. Tariffs against imported motorcycles were looming and turbo charging was a way to keep the power but lower the displacement. Yamaha followed the big-faired design with the XJ650 Seca but with an air-cooled inline four displacing 653cc. One of the advantages of the turbo was the ability to adapt an existing motor.

The most obvious element of the four bikes beyond the ability to place the word “Turbo” prominently on the bodywork was that with a turbocharger it was possible to get more power from a smaller engine, and particularly a high-revving, small motorcycle engine. The Kawasaki GPz 750 was both the largest displacement, and along with the rarer Suzuki offering, the sportiest of the turbo bikes, producing 95 hp compared to 85 for the Yamaha XJ650 and 82 for the Honda. The Kawasaki and the Suzuki XN85 were the only bikes with chain drive. The Suzuki’s model name comes not from its displacement but from the hp produced by the 673cc engine. The Seca and CX could be considered sport touring machines with the ability to wick up impressive numbers when necessary while the other two trended toward a full time sporting nature.

But they weren’t what consumers wanted. Within a couple of years the potential gains of a turbocharger in a heavy motorcycle with a small engine were overwhelmed by the initial flood and then torrent of race replica bikes that used the benefits of less weight and larger engines to make turbocharging a thing of the past. Besides, turbos had negative aspects that were difficult to deal with in automobile applications let alone motorcycles. The heat could be tremendous and the power was far from linear—there was often “turbo lag” as the system waited to respond to increased engine load with a sudden burst of power. Big normally aspirated Ninjas, GSX-Rs and CBR1000s were simpler, faster and more predictable to ride. And except for perhaps the Suzuki XN, they all looked a lot better.

What do we have left to say about turbocharged motorcycles? If you can find one of the original four in good shape you are exceedingly lucky and will have a collector item. You can never go back and believe that the bikes are fast or performed well compared to even mid-range bikes of today, but they were a part of a very short period of innovation. And it was over 30 years ago for all of the machines. What they could do back then considering the technology was impressive even if they were not the answer to the rider’s need. 

Kawasaki has obviously upped the forced air induction the ante with the supercharged H2 so it is very likely that history will repeat itself and there will be further forced air induction machines coming to market. Several years ago Suzuki revealed its Recursion prototype, which is a turbocharged 588cc parallel twin producing a factory-spec 100 hp. 

The company claims that fuel consumption is less than half that of a normally aspirated 600 producing equivalent power. This may well be where the future of turbocharging of motorcycles exists. The increased efficiency of very small engines producing maximum horsepower and torque. It is how the auto industry is attempting to meet higher fuel efficiency standards and for that industry it is working. 

To think that the same will not happen to motorcycles is likely short sighted. With the advent of features such as variable power modes, the spectre of turbo lag as it related to those 1980s offerings should be a thing of the past. Whether superchargers or turbochargers will prove dominant is for the future to decide.

By John Molony Canadian Biker Issue #315


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