Turbocharging engines is nothing new. In 1909, a native of Switzerland by the name of Herr Bchi came up with the idea of using the exhaust gas from his diesel engine to drive a turbine to compress air and "supercharge" the intake side of his old knocker. As a result of Bchi playing with turbines instead of making cuckoo clocks, turbocharging has become almost commonplace in the world of big diesel-engined commercial vehicles and normal practice at the performance end of the market, but it has yet to make any sort of real mark in the world of production motorcycles.
Over-the-counter turbochargers have been available for big four-cylinder bikes for years, but these bolt-on performance kits are only as good as the amount of work needed to make them work properly and harmoniously with the engine. Honda, Yamaha, Kawasaki and Suzuki built turbocharged motorcycles in a mad fit of 1980s one-upmanship, and the corporate war between the giants spawned a trio of technically over-complicated and bizarre bikes...and the world's first successfully turbocharged production bike.
Honda was the first into the fray with a turbo version of its CX500, and the bike that launched a million yawns was pretty useless. Yamaha also had a fairly bland contribution-the XJ650. Suzuki had another key to the comatose cupboard in the form of the XN85-a motorcycle that had very little to offer either.
After the other three shot their corporate bolts, Kawasaki jumped out of its pajamas and gave them a severe kick where it counts with the GPz750 turbo-the only real production turbo offering sport ability and street cred. The turbo Kawasaki was the best of the bunch-a bike with the aesthetics and menace of a switchblade and a simple, effective and compact turbocharging system that would howl along at 140 mph and knock out standing quarter-mile times in the high 10s.
The turbo fad quickly wore out, though, and the manufacturers focused on race replicas as their flagship performance models instead of gimmick bikes. Since those days, the private sector has picked up on turbocharging, and it's trickled down from strip racers to street riders.
But how do these wild contraptions actually work? The function is rather simple, but getting a durable application can be a bit tricky. A conventional motor's ability to produce horsepower is dependent upon the rate at which the engine can burn the fuel and air mixture that is fed to it by injectors or carburetors. A turbocharger is a device designed to increase the mass of airflow into an engine and therefore increase the engine's capacity to produce power. In other words, a turbocharger is a mechanical pump designed to force-feed more air into the engine; more air means more fuel burned, which equates to more power. But that has a downside-the by-product of more heat puts more strain on the mechanical parts of the engine.
Leaving the financial facet of the equation alone for a minute, turbocharging is a way of getting something for nothing. The gas exiting the exhaust system is fast and hot, and following its exit into the atmosphere, it serves no useful purpose at all other than upsetting your yogurt-and-sandals neighbor at 3 a.m.
The role of a turbocharger is to harness this stream of wasted energy to produce more horsepower from within the engine. In effect, a turbocharger is driven off the energy generated by the flow of exhaust gas, whereas a supercharger is mechanically driven from the engine by way of belts, chains or gears and therefore uses power from the engine to create even more power. A turbocharger, however, is basically a turbine driven by the engine's exhaust gases that produces more power without sapping any energy from the engine.
A typical turbocharger is made up of three basic components: a turbine housing, a bearing housing and a compressor housing. The exhaust gas spins the turbine, which then spins the shaft that is lubricated in the bearing housing. The shaft then spins the impeller inside the compressor housing, thus compressing the incoming fuel and air mixture before delivering the mixture to the cylinders.
Instead of a conventional exhaust system, the turbocharger unit is connected directly to the engine by one or more exhaust pipes. The hot, fast flowing gases are directed against the blades of the turbine, causing it to spin, which in turn rotates the shaft and the compressor impeller. This impeller inside the compressor housing draws the mixture of fuel and air through the carburetor or fuel-injection venturi and forces it through the "snail shell" housing where it is compressed and fed to the intake side of the engine under pressure. This scenario is what is known as a "draw-through" application.
The other common method of turbocharging an engine where a charge of compressed air alone is blown through the carburetors or fuel-injection venturi is known, predictably enough, as a "blow-through" application. The blow-through turbo is fast becoming the turbo unit of choice, with the added advantage of intercooling. The advantage of blowing the air through is that this method gives far superior throttle response and therefore a great deal less "turbo-lag" than the draw-through turbo.
The purpose of an intercooler is to cool the incoming pressurized air and thus lower the temperature of the charge prior to its passage. The main advantages of an intercooler are a reduction in combustion chamber pressure and lower running temperature for the engine as a whole; both factors thus reduce the strain on the working parts of the engine and add to its longevity.
There is another vital component within the turbocharged package, and that small but perfectly formed item is the waste gate. As its name suggests, the waste gate is a preset pressure-release valve that expels surplus exhaust gases, and on many modern turbo units the waste gate is an integral part of the assembly.
There are many different turbocharging units on the market that are produced specifically for motorcycle use and are available as bolt-on kits. But keep in mind that turbocharged motors don't suffer fools lightly, and the slightest leak will melt a piston like a Mars Bar under a sunlamp.
When properly set up, a turbocharged motorcycle offers one of the zaniest white-knuckle experiences you'll ever enjoy. If you haven't ridden or owned one, you need to.
Outlet Pipes For The External WastegateDiverts the exhaust gasses that are released by the wastegate when the pressure inside the exhaust manifold gets too high.
External wastegate (this setup has two)
A wastegate is simply a poppet-type valve fitted to the exhaust manifold pipework between the engine and the turbocharger. When the pressure inside the exhaust manifold reaches a predetermined level, the wastegate opens, reducing the pressure and preventing the turbo from overspinning and getting damaged. Note: Not to be confused with a blow-off valve (BOV) or dump valve, which is a similar type of valve fitted on the inlet side. A BOV opens when the throttle is closed to change gear, which causes the pressure to increase in the intake manifold between the turbo and the throttle body (ies). This pressure spike would normally blow back through the turbo compressor wheel, causing it to stop spinning. The result can be long-term damage, as well as increased turbo lag as the compressor spools up after the throttle opens again. The BOV vents the pressurized air back into the inlet side of the turbo, preventing the pressure spike.
Main Exhaust Outlet
Expels spent exhaust gas from the turbine wheel.
Inside the shaped housing is a fan wheel that sits on a common shaft with the compressor wheel (5). Pulses of hot, fast gas from the engine exhaust ports travel through the exhaust manifold and into the turbine housing, turning the turbine wheel as they go.
Inside the housing is a shaped fan wheel, which is turned by the compressor wheel on the same shaft. As the compressor fan wheel spins at up to 120,000 rpm, it sucks air in through the housing intake and blows it into the inlet manifold. This pressurized air increases the amount of oxygen inside the cylinder during each combustion, allowing more fuel to be burnt and more torque and power to be produced.
Pressurized Air Outlet
Feeds the pressurized air from the compressor unit to the inlet manifold (or "plenum chamber"). On turbo installs, the airbox has to be tough enough to hold the high-pressure air generated by the turbo without expanding (or even cracking). In high-power installs, that often means an aluminum or stainless fabricated box.
The Good, The Bad, And The Ugly.
The Big Four got into a battle using turbos asthe weapon of choice, and only one succeeded in making a bike that hasn't been the butt of countless jokes. Kawasaki's GPz750 had the right mix of sportiness, performance and sex appeal that made it actually desirable, whereas the other bikes were all a bit too humdrum for most.
1984 Kawasaki GPz750
1984 Suzuki XN85
1982 Honda CX500, 1982 Yamaha...
1982 Honda CX500, 1982 Yamaha XJ650