ScienceofSpeed Intake Air Bypass (IAB) Delete Kit - NSX, 1991-05


The factory Intake Air Bypass (IAB) system, also known as the Variable Volume Intake System (VVIS) is a vacuum-operated set of valve plates that alters the volume of the intake depending on load. The valve plates are fastened with screws that are known to loosen with time. The result has led to catastrophic engine failure.

ScienceofSpeed has experimented with various methods to secure the valve plates. However, it is difficult to ensure the long-term durability of the repair.

ScienceofSpeed then investigated what the effect of simply removing the IAB system would be - and to our surprise, in our testing - the 3.0L engine with headers & exhaust showed little power loss at high RPM gains, while an all-factory 3.2L showed little power loss and a slight amount of power gain at high RPM.

The included kit includes everything required to install the supplied CNC-machined 6061 aluminum spacer that replaces the IAB assembly. This includes replacement gaskets, crush washers, and vacuum hose plug.

With this kit, you can ensure that a failed IAB valve does not damage your engine - and pick up some additional performance at higher RPM as well.

Note: this kit is compatible with the factory intake manifold only. Supercharger kits from ScienceofSpeed and Comptech remove the IAB system. This kit is recommended for factory naturally aspirated engines, as well as turbocharged engines.


  • Replaces troublesome factory component that can result in engine damage.
  • Increase reliability.
  • Complete kit includes everything required for installation.


  • Precision CNC-machined aluminum plate.
  • IAB top and bottom gaskets.
  • EGR tube gasket.
  • Aluminum sealing washers.
  • IAB hose plug.
ScienceofSpeed Intake Air Bypass (IAB) Delete Kit - NSX, 1991-05