Todd: for aluminum, I typically start with an aggressive polish like Simichrome and a sewn cotton buffing wheel attachment for a drill. (this process is for smooth metals. for "as cast"...you need to use a sanding wheel).
I get the finish in the condition I want, then move to English Custom with another clean buffing wheel. Following that, I use Meguiar's NXT Metal Polysh and another cotton buffing wheel. Mother's Billet Creme works well as a final step.
My Team III wheels
For harder metals like stainless, I start with Simichrome and 1,500 grit paper and work my way to 2000 grit. Then use the buffing wheels similar to above.
Stainless SLP Exhaust
Finally, are you sure the exhaust is aluminum? Generally that metal is a poor choice for exhaust due to the corrosive action and heat of exhaust systems.
Toto