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the intake, also referred to as a dual runner intake, is featured on the B18C1-4 and H22A1-4 motors. the intake runner incorporates 8 runners, 1 for each cylinder, unlike the normal intake which has 1 per cylinder.
there is also a butterfly valve on four of the runners controlled by a solenoid and vacuum pressure. in the case of the H22A, the motor runs on 4 runners to breathe. at 5200rpm, the solenoid is actived, and vacuum pressure opens the butterfly valves, thus allowing all 8 runners to feed air into the cylinders. the system works in the same way on the B18C, but at a different set rpm.
this system allows for increased performance at high rpm, while still retaining proper intake air velocity to produce good low RPM torque. the trade off is that high rpm performance suffers slightly due to intake air turbulence caused by the dual runner design.
due to the slight decline in high rpm performance compared to a single runner, large bore design, Honda engineers chose to use a single runner design, a la B16A, for the B18CR/B18C5 Integra Type R motor.
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