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Honda Cylinder Deactivation
11/2/2006
By Barry Winfield

Honda showed this prototype of a CBR1100XX with variable cylinder management at a recent technology exposition at the company's Tochigi Proving Grounds in Utsonomiya, just north of Tokyo. Using a variation of its VTEC variable valve-timing and lift system, called Hyper-VTEC, Honda selects two-, three- or four-cylinder operation depending on engine speed and load. The result, according to company spokesmen, is a fuel efficiency improvement of 30% compared to the stock bike.

Like all of Honda's VTEC mechanisms, the principle behind its operation is the use of oil pressure to slide locking pins in and out of valve followers. On the CBR1100, Honda uses ingenious valves with telescoping sections that either idle the valve or lock it back into normal operation, depending on which mode the computer selects. When one or two cylinders are de-activated, the valves close and the pistons simply travel up and down in the bores, using whatever air is inside the cylinders as a spring.

Unlike cylinder de-activation mechanisms we've seen in car engines such as Chrysler's Hemi V-8, which runs normally until the vehicle has achieved a low-load cruising speed before switching off one bank of four cylinders, Honda's VCM starts up the bike on just two cylinders, switches to three as speeds rise and more power is needed, and only goes to four pots when the revs are right up and the rider's looking for warp speed.

Although I'd gone to the Honda function in my capacity as an auto writer, the presence of a variable-cylinder motorcycle piqued my interest, and I had to ride the thing. Borrowing a jacket, a helmet, and gloves from Honda, I set off around the high-speed oval behind one of Honda's test riders. He varied the speed a little during the laps we took, but never really provided an opportunity for a foray to the redline. Nevertheless, by slowing down a little, downshifting and winding it on, I could get the CBR back on four cylinders, pulling like the missile we know the Blackbird to be.

The rest of the experience wasn't that suave. When the bike starts on two cylinders, it sounds a lot like an inline-four with a bad misfire. Sure, 650cc is enough to tug the bike off the line and propel it on its way, stuttering and hammering along in a manner that will put a mechanically sympathetic rider's teeth on edge. Having the third pot chime in isn't a lot better, since the exhaust note is now like an inline four with only one cylinder out. By the time the fourth cylinder joins the party, it's to the considerable relief of the rider.

I asked Hayato Maehara from Honda's engineering design department why they hadn't taken the Chrysler route of having the bike run smoothly and normally during low-speed operation, then switch off two cylinders once cruising at speeds that require relatively little power to maintain. His answer was simple: "You don't achieve a 30% fuel saving with that strategy."

Perhaps not, but an application this dedicated in its pursuit of frugality on a machine purchased largely for its power and acceleration seems a little oxymoronic. The irony here, too, is that you need multi-cylinder engines to make variable cylinder management possible.

But this was just an experimental prototype. There's nothing to stop Honda from providing this technology with a switch. That way you could commute to work on two or three cylinders, then switch the VCM off on the weekends to go rip canyons with your riding pals.

Still, the esthetic considerations relating to a machine that feels and sounds like a bike with a bad misfire much of the time seems to us to be a major roadblock to this particular technology.