VTEC operation applies for Honda D15Z1, D16Z6 & B16A3 engines.
Honda Civic 1.5L – D15Z1 SOHC
D15Z engine is equipped with 4 valves per cylinder. At low engine speeds, the primary intake valve operates with normal lift characteristics and secondary intake valve lifts slightly to prevent fuel accumulation in intake port.
When engine speed exceeds 2500 RPM and other conditions are met (determined by ECM), oil pressure is applied through a spool valve to timing and synchronizing pistons located in valve rocker arms. Synchronizing piston locks primary and secondary rocker arms together, causing both valves to operate at the higher lift and duration of the primary cam and valve. This system of locking rocker arms together is designated VTEC-E.
Honda Civic and Del Sol 1.6L – B16A3 DOHC and D16Z6 SOHC
B16A and D16Z VTEC system used on the 1.6L engines differs from the VTEC-E system used on the 1.5L engine. VTEC system used on the 1.6L engines functions in the same manner as the system on 2.2L engine on Honda Accord. Valve function changeover is accomplished when certain conditions are met (as determined by ECM).
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