In the last ten years we have seen (and ridden) the results of an incredible horsepower race among the “Big Four” Japanese manufacturers. Think back to 1994 – if someone had told you that in 10 years you would be able to buy a 100hp 600 or a 1000 that puts down nearly 170hp, right off the showroom floor, would you have believed them?
Many factors have contributed to the increased horsepower of the current crop of Japanese 4-cylinder sport bikes. The switch from carbs to fuel injection, combined with more advanced engine management computers, have made possible much more precise fuel tuning. This in turn has allowed higher compression ratios, which allows the motor to take advantage of more aggressive cams. A multitude of factors dictate the maximum horsepower achievable on a street-tuned naturally aspirated motor, and changing one can allow changes/advances to others.
Unfortunately, it seems unlikely that we will see more big jumps in horsepower in the near future. Consider the fact that current MotoGP bikes, which feature purpose-built racing engines running on advanced race fuel and tuned with engine management systems which cost more than the average production sportbike, are currently putting out approximately 240hp/liter (equating to around 240hp from a 990cc motor). The most powerful production 4-cylinder sport bikes (like Kawasaki’s new ZX10) produce in the neighborhood of 170hp/liter on pump gas (while still meeting emissions regulations). Unless you want to run your streetbike on $12/gallon race fuel, there isn’t a whole lot of room left. It seems likely that 4-cylinder sport bike horsepower will peak at around 190 hp/liter in the near future (I am discussing wheel horsepower figures).
One would think that 115hp 600s and 190hp 1000s would be fast enough, but it is clear that the consumer will continue to demand more power for the forseeable future. Each of the Big Four wants the prestige and selling power that comes with having the most powerful sport bike available.
Where will the Japanese find more power? Why not turbochargers? Relatively recent developements, particularly compressors using ball-bearing center sections, have all but eliminated the dreaded “turbo lag”, at least in low-boost applications. The popularity of Mitsubishi’s Lancer Evolution and Subaru’s WRX (in standard and STi trim), both of which use small-displacement turbocharged motors, may herald a resurgence in the popularity of factory turbocharged automobiles. Mitsubishi’s Lancer Evolution features a 2.0 liter, inline four-cylinder which is considerably less technologically advanced than current Japanese inline four sportbike motors, yet still manages to put out a claimed 271hp.
With a small, ball-bearing turbocharger system optimized for lag-free response at between 7 and 12 psi of boost, I would venture to say that 220hp/liter is not out for a street-tuned inline four. Although not many people would feel that a ZX-10 needs 50 more horsepower, how many would go for a 135hp 600?
Will a major Japanese manufacturer release a factory-turbocharged sport bike within the next 3 years? Time will tell, but considering the amount of money they must be spending on engine R and D for relatively small gains, I would say it seems likely.
