I put a dual 2 1/4" exhaust with an H-pipe on a 70 Swinger with a 318, and it really woke it up. the stock exhaust on a 318 is very restrictive. It's the first thing to change for increased performance as it gives the most benefit.
Krazy kuda is right about his experience. More than likely though he was running it with a 4 barrel and flooring it Alot lol. In my opinion if I was driving a 318 2 barrel with 2.76 gears, in the city nonetheless, it would be getting the 2 inch exhaust. Like I said before torque and velocity go hand in hand. Besides 2 inch is easier to install anyway given the small space to work with around the tank and rear end. I'm sure some will argue though...
