Honda has developed a new version of the VTEC variable valve timing and lift specifically for two-wheelers.
While Honda has offered Hyper-VTEC on its bikes since the 1990s, the motorcycle system is actually a rebranded version of the earlier REV arrangement, used on the CB400 since 1983. It shuts off two valves in each cylinder at low revs, converting a four-valve into a two-valve.
Honda’s true VTEC system started on cars in 1989. It features two separate cam profiles for each valve, allowing completely different timing, lift and duration. The engines switch between cam profiles by engaging or disengaging an additional rocker, using a hydraulically-moved pin. But this system has never been used on bikes.
Now Honda has created a true VTEC system for motorcycles. More compact and simpler than the original, it still has the same effect of switching between cam profiles, but uses finger-followers between the cams and the valves. To switch between cam profiles, the entire camshaft is shifted sideways.
Both the intake and exhaust cams can be moved, separately if required, to switch between mild cam profiles at low revs – with short duration, less lift and little overlap – to wilder ones at higher revs. This offers better low-end torque and top-end power, and reduces emissions.
It’s normal practice for ideas to be trialled on single-cylinder test engines, so the patent doesn’t necessarily mean the technology is destined for a single.
By Ben Purvis