So how do these mechanisms work? What do they do to alter valve timing? We’ll take Honda’s VTEC first, as it was the first motorcycle VVT system for worldwide sale. VTEC stands for Variable Valve Timing and lift Electronic Control. There are many VTEC variations, but the one on the VFR800 motorcycle is the one we’ll look at. This engine has four valves per cylinder, so there are two intake valves. There are two rockers and two cam lobes for those intake valves. At lower engine speeds (up to about 6,500 rpm) one cam lobe operates one rocker and one valve. The second valve remains closed. At a pre-determined engine speed an electronically controlled oil valve opens, and oil pressure slides a pin sideways, locking the two rocker arms together. The second rocker is now depressed by the second cam lobe, and since the rockers are now locked together, both valves are now operated by the second cam lobe. The second cam lobe has different timing, lift, and duration from the first lobe. VTEC isn’t a progressive system—the change is discrete, so it’s all-or-nothing, leading to a noticeable and sudden difference in performance.