Polishing sand cast pieces takes an amazingly long time, especially if you don't have the right tools for the job.
I've done small pieces and it takes forever, the little nooks and crannies in an intake would be tough.
If you want to give it a go though... I ususally,
1) Grind the casting grain off with a grinding wheel
2) sand with a DA starting with 80 grit, then 200, then 400, then 800.
3) wet sand by hand with 1200 grit and then wetsand with 2000 grit
4) polish with a dremel with Mother's Aluminum polish.
That will get you a mirror finish but the problem is that bare aluminum oxidizes really quickly. You will need to polish it by hand on a weekly basis to keep it shiny. A lot of work.
You can have the bare aluminum brite dipped and annodized to prevent oxidation. I use "Colors Inc." out of Indianapolis.
With the cost of materials and time it takes, I think it would a tough sell on polishing an intake myself.
Edelbrock sells all of their manifolds in "polished" form now. The price is about $100 bucks more. Well worth it if that's the look you want. $100 vs 100 hours of time
