VTEC EX­PLAINED

Motorcycle News (UK) - - This Week -

Honda’s Vari­able Valve Tim­ing and Lift Elec­tronic Con­trol (VTEC) was used in cars in the 1980s and first ap­peared on bikes in the Ja­pan-only CB400 in 1989, but it wasn’t un­til the 2002 VFR800 VTEC that it gained no­to­ri­ety. Like most mo­tors, the VFR has two over­head cams that op­er­ate two in­take and two ex­haust valves per cylin­der with a bucket and shim-style valve train. Be­low 7000rpm a hy­drauli­cally-op­er­ated pin in­side the valve lifter bucket of one in­take and one ex­haust valve is moved aside by oil pres­sure. This al­lows the bucket to move up and down un­der the cam with­out op­er­at­ing the valve, ef­fec­tively mak­ing the en­gine a two-valve mo­tor. Above 7000rpm, the oil pres­sure is re­leased and a spring forces the pin back into the path of the valve stem, al­low­ing the cam to op­er­ate the valves again and re­turn­ing the en­gine to four-valve. In the­ory, a two-valve mo­tor gives bet­ter low-end per­for­mance while a four-valve one is bet­ter at high revs, so a VTEC en­gine gives you the best of both worlds.

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