Motos

It’s hard to believe a decade has gone by since the 636cc Kawasaki ZX-6R first came to our shores. The beefed-up middleweight shook up the category with its displacement advantage over its rivals, and with the 600cc ZX-6RR variant being sold alongside, both racers and street riders were happy. But in 2007, after four years of success, Team Green stuck with tradition and axed the 636 from itslineup to continue with a 599cc version.
However, with many manufacturers focusing on literbike updates lately, the middleweight category has remained relatively stagnant, save for a freshened up Suzuki GSX-R600 in 2011, and, of course, MV Agusta’s beautiful F3. Known for shaking up the status quo, Kawasaki is looking to jolt some life back into the class with the 2013 ZX-6R. The magic number behindthe new ZX: 636.



It's baaack. After a seven-year absence, Kawasaki has revived the 636 in the 2013 ZX-6R. Competitors should be worried.

Yep, Kawi has brought back the successful formula last seen in 2006, adding 37cc more displacement to the existing 6R engine, resulting in a motorcycle that’s powerful on track and flexible on the street. The interesting twist, however, is aconspicuous omission of its 600cc ZX-6RR counterpart. More on that later.

After seven years away, one might wonder why bring the 636 back now? “Since 2007, when the ZX-6R went back to 600cc, the bike was focused on the track rider. Now, engineers wanted to appeal to a broader range of riders,” says Kawasaki Product Engineer Yoshi Sakakihara.

What’s Old Is New Again

In order to achieve the increaseddisplacement, Kawasaki engineers started with last year’s 599cc engine and increased its stroke 2.6mm to 45.1mm (compared to 42.5mm) while retaining an identical 67mm bore. But why stop at 636cc? If Kawasaki is looking to be different and think outside the lines, why not go even bigger?


Based on the outgoing 600cc engine, Kawasaki engineers increased stroke and improved breathing, whilestrengthened internals help it cope with the extra power.

“We wanted to maximize displacement without increasing bore diameter,” says Sakakihara, adding that a larger bore would result in a wider chassis and a heavier-feeling motorcycle due to the gyroscopic effects of the bigger pistons and running gear.

A number of internal improvements to the engine were made to accommodate the bump in power.Revised Intake and exhaust ports help meet the power characteristics Kawasaki was aiming for, while dual injectors are ditched in favor of single units. This not only saves weight, but also accounts for the 11% increase in airbox volume.

Each injector sprays a super-fine 60 microns and together deliver a 20% higher fuel flow rate compared to last year, negating the need for twin injectors,says Kawi. Intake cams receive 3.0 degrees more duration, while both intake and exhaust cams get slightly more lift. Compression ratio is cut a smidge to 12.9:1, from 13.1:1, while pistons and connecting rods are reshaped and strengthened to cope with the extra power. The rods are 1.5mm shorter to offset the longer crank throws.

All four header pipes are now connected via cross-over tubes intendedto increase low- and mid-range torque. Previously, only headers 1-2 and 3-4 were connected. The silencer and sub-chamber combination meets both U.S. noise and Euro 3 emission regulations, meaning regardless of which side of the Atlantic you’re on, the ZX-636 will be tuned to make the same power. Some might recall previous generations of ZX-6R shipped to the States were tuned differently to meetU.S. noise regulations, ultimately making less power than its European counterpart. Those days are gone.


A new, lighter slipper clutch from F.C.C. shaves 700g compared to last year. Aluminum construction and a switch from six clutch springs to three are major contributors to the weight loss.

Harnessing all this power is a new aluminum slipper clutch from F.C.C. claimed to be 700 grams...