Project NSX: Part 5 – We Dyno Test A Ported Intake Manifold and Headers With the VVIS plate’s butterflies (in Red) closed, the throttle body feeds the relatively shallow and divided plenum, which feed the runners that go into the heads. Due to the small volume, low end torque is improved. With the VVIS butterflies open, the intake manifold plenum is no longer separated from the lower plenum. Since the lower plenum is only connected to the throttle body via the six butterflies, the volume is indeed increased but there is no additional air that flows through the butterflies from the lower plenum.
While the VVIS plate improves low-end torque by reducing the plenum’s volume at low RPM, in forced induction applications there is a benefit at both low and high RPM by reducing the restriction and turbulence of the intake by gutting the system altogether.
We first modified the VVIS plate by cutting out the butterflies and welding up the holes for the actuator. Next we modified the upper plenum by cutting out the bridge and center wall that divided the runners on each bank. Now after the air passes through the throttle body, there is a single, open plenum which feeds all six runners. With the VVIS plate gutted and the center dividing wall of the manifold removed, air enters a single, open plenum with a smooth path to the intake runners. This has proven to be advantageous in forced induction applications, which is good because our turbo motor is currently being assembled.