I've done a few of these intakes over the years and when I show the pics I was asked to post a how to do it so here goes. This will be a long post so if you have any comments I'll ask that you wait until you see the final results. About 35 pics in all so it should explain all you need to know. The tools I'll be using are standard die grinders but the bits are really course so the aluminum won't clog up in the bit as much. The WD-40 is to spray on the bits occasionally to help keep them from building up and it does work to some degree. You can do this with an electric die grinder as well but since I work in a shop and I had a half day off I figured the boss could pay the electric bill. If you look at the die grinders I have put a regulator on each one to control rpm a little easier. If you're using an electric one you can use a router controler to control the rpm. Most of the time you will have the high rpm to make for a smoother cut but when using the flapper wheel go slower so you can control it better.
The first thing you will need to do is to mark the maximum cut for the top. A little dyechem is great but if you don't have it a magic marker will work just as well. Make a line from the edge of the front and back barrels and use a strait edge.
The first thing you will need to do is to mark the maximum cut for the top. A little dyechem is great but if you don't have it a magic marker will work just as well. Make a line from the edge of the front and back barrels and use a strait edge.