I have the offy manifold, and fenton headers on my 216, daily driver. I've put on about 8,000 miles on the set up. I ran it for several thousand with Rochester b's, and then rest has been with Carter W-1s. I have aluminum pistons, and my 216 is over-bored. I was careful in setting them up, and syncing the carbs. I get slightly better mileage, and a little more power. Another 10,000 miles, and it will have paid for itself. It looks cool, sounds cool, and cost money. I probably wouldn't do it again though. But it is cool.
