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The Honda Insight's engine employs a newly designed VTEC system. In this system, the cam followers of the intake primary rocker arms are fitted with rollers that minimize friction on the cam's contact surfaces. (Each roller turns on a needle roller bearing.)
The VTEC rocker arms are a new, compact, low-friction design, adapted from the S2000 roadster, with the VTEC switching mechanism (pistons) located coaxially with the roller elements. This new design reduces the reciprocating mass of the valvetrain, for more reliable high-rpm operation, and also allowed Honda engineers to reduce valve-spring load by 30 percent.
During acceleration, when engine speed reaches 2500 - 3200 rpm the primary and secondary rocker arms are locked together by the VTEC pistons. During deceleration, when engine speed drops to 2300 rpm the primary and secondary rocker arms separate. The exhaust rocker arms are made of aluminum.
The IMA engine's single overhead camshaft (SOHC) cylinder head uses a compact chain drive in place of a toothed belt, and features a new compact, low-friction VTEC valvetrain that uses a common shaft for both the intake and exhaust rocker arms. Placing all the rocker arms on one shaft eliminates the need for a second rocker-arm shaft, so the valve mechanism can be more compact.
An additional advantage of this design is its narrower included valve angle that better centralizes the stratified air-fuel charge around the spark plug for quick light-off and more complete combustion.