I made on for my Plus 4. I just bought a suitable ITG filter box and some appropriate tubing from a automotive supplier online and a length of aluminium tube. I had to make up the brackets to support it and modify the radiator surround to get access to the air from the front. I think the ITG filter made the most difference although based on the reported temperature from the engine management system it did lower the intake temperature somewhat especially at speed. The big surprise was just how hot the air is once it gets in.
You may find on a Plus 8 that space is an issue for an air box of an appropriate size.
Dave
