Been a long time since I was on here, but have been scouting the site lately as I recently picked up a '99 GTP with 180,000km. Thanks for the how-to nawarkk, I used a K&N RU-1785 3.5x5x8.5" straight filter for mine, and man does the supercharger scream, absolutely love it.
I'm thinking I'm going to need to pick up a new piece of PVC though, I bought one like yours, 3" with the small OD on the one side, however it seems the wall thickness on mine is a little thinner - the heat from the engine and the forces from the clamp seem to have turned it into an egg shape and the clamp had loosened off a little bit. I wonder has anyone else suffered from this problem? My engine temperature floats around the 85-90*C mark (185-194*F), which seems normal to me - granted I'm also using the boost a lot (really enjoying the car, lol) so I'm sure the supercharger is packing a heck of a lot more heat under the hood as well.
