I ran cat-less on one of my old cars for a few weeks and I swear I could actually hear mother earth crying. OK that's a bit dramatic but you should be prepared to smell like hydrocarbons.
IMO it's not worth the hassle, expense nor the decrease in air quality. Pollution is so bad in Dallas they tell you to stay inside on some days. Apparently working outside here is like smoking a pack a day. Wether you believe in anthropromorphic (sp) climate change or not, carcinogens are bad and totally not worth a few HP here for the sake of bragging rights.