2 barrel with stock exhaust??
There's enough meat there to open it up, just probably not all the way to the 2.25" Super Six size
Not sure if this helps the discussion or not but I have two Super Six exhaust manifolds, they both measure 2.00" ID where the down pipe bolts on. The factory muffler pipe is also 2.00" ID. There is some extra material in the manifold exhaust port, but it would take a far better person with a die grinder than myself to hog out the ID to 2.25". The smallest OD I measure on the manifold exit is 2.61". That means there would be a hair over 1/8" wall thickness after taking this out an extra 0.25". I will be leaving this alone, as a look inside the manifold doesn't appear to have a lot of options to open it up. Maybe a stock slant manifold would be different, but that's what I know about a Super Six. This came off a 78 Volare I took apart a few weeks ago, and that 2" pipe goes all the way to the muffler. I have no idea what size pipe goes from the muffler to the rear tail pipe, this car had nothing behind the muffler.
I won't have any real-world suggestions until spring, when my Valiant is reborn. But I read a
lot on this site and dot org. What I gather from the slant gurus is better breathing in and out is vital to performance. A dual exhaust manifold setup (Dutra Duals or a homemade version of the same, or headers) going into a wye then to the muffler and out the back as a single exhaust is the way to go, and it's what I'm going to do.
My current set-up is a one-barrel into a stock exhaust, but my pipe beyond the manifold is scrawny, like 1-5/8" or so if I recall correctly. If I had your scenario I would at the least either try to hog out the stock manifold or find/make a dual manifold into a single 2.0-2.25" pipe to the rear bumper. If you could find a Super Six exhaust you'd be ahead of the game. And yes, everything I know says a 2-barrel is a better deal. Good timing and tuning should make a noticeable difference.
