Info ZX2r 1989 exhaust

Is anyone able to explain how a pressurized NA airbox works?

Only my basic knowledge, so happy to be corrected...

They don't work with CV carbs. The ZXR250 has an air inlet on the LHS fairing...this can be mistakenly construed as forming part of a pressurized airbox system as it faces forward into the oncoming air...it is not. The air coming in does not pressurize the airbox, but it is cold and gives the engine a bit more access to fresh air at higher speeds and higher revs. A "pressurized" airbox has large volumes of air pushed into a contained area, so it builds a little bit of pressure. I doubt it's much higher than normal atmosphere, but it is cold and ready to use by EFI throttle bodies or FCR carbs. Supercharging and turbocharging build a pressurised area inside the manifold and then push that into the combustion chamber.