I wanted to try and document this a bit while it was still fresh in my mind, but I had a race to get to at the end of the week so it's a been a bit since I did it. However, I will do my best to tell you what I did and why. I lost a few pics of the process but I'll describe the best I can what I did that isn't shown.
To start off you'll need these:Just one I could only find a pic of four of them. Make sure you get the 6" shank as the manifolds are pretty deep.
You'll also want a decent air compressor and die grinder that can operate at the speed of your bit for extended periods of time.
Plan to spend between 4-6hrs on this and it's VERY messy. Be sure to wear eye protection as well as some sort of face mask/respirator. The carbon dust is not fun if inhaled.
It's easier to start with the downpipe as it's a little easier to get going and get the feel for things.
Start off by getting the exhaust manifold 'back welded' as seen below:
This will allow you to fully port the inside of the downpipe, but the welding will leave some 'dingleberries' on the inside:
You want to get rid of these, as well as try and smooth the transition to gasket size:
You'll notice I didn't quite go to gasket size as my weld wasn't THAT big and the transition would be sharp had I gone bigger. This is personal preference but it works. I cleaned that up with a sanding bit but didn't polish it much more then shown.
Now to the manifolds, these take FOREVER so be patient. Your hands will hurt after a bit, so stop and come back later.
Notice not only the matching of the gasket but also the smooth transitions around the turns. Getting in there deep is where it matters.
I only finished it with the grinder plus some 80 grit final finishing. Some will argue that full polishing will hold some power as well. I didn't have the time to find out.
I don't have pics of the manifold where it meets the downpipe but it's ported just a little less then the downpipe so that there's a step up to it, roughly .5mm large.
I hope that explains some things about porting the manifolds now that we hear so much about it these days.