http://www.ruffstuff.com/pages/carbide.htmlI like the oval, shape E burrs. Double cut, 6" long in a variety of sizes. You can get by with just a 3/8", but a 1/2" speeds things up in the long straight stuff, and a 1/4" can make the fine tuning around the guide boss much easier. Those are the three sizes I recommend. Obviously do not start the burr unless it's against some material, do not free spin it (in other words, not have it against material when you're spinning it at speed). You'll want the walls to look straight and as smooth as the burr will get it before you ever touch it with a sanding roll. For cast iron I like 40 grit sanding rolls, but if you spin them too fast they tend to come unraveled. 60 grits hold up better but they don't remove material as fast. I like a combination of 40, 60 and 80 grit. When they start to leave black smears across the port, put a new one on. Trying to use up the whole roll makes for a frustrating port job.
Also, having a good grinder makes the job so much easier. The Suhner grinder (the expensive one) on the website I pasted in is pretty much the Mercedes of all porting grinders. Milwaukee makes one, but your forearms will feel it and they tend to be burr benders as they spin up immediately and only have one speed. Air grinders work, but you don't have as much control unless you get one of those long air grinders, which I have had no experience with.
Grind away!
One more thing! Have a spray bottle of light oil on hand. It'll make the burr last a lot longer. And have your shop vac ready to vacuum out the cuttings. A fan set to the side of the head blowing across it works pretty good to keep the dust out of your lungs and eyes.
