A few weeks ago I had true dual exhaust installed on my 1989 Formula. I was fortunate enough to already have a Formula with the dual catalytic convertors in place. I assessed several options as to how to install a true dual exhaust system, as the space is tight and options are very limited to say the least. I still have factory exhaust manifolds, and the cats were still in place, as was a rotted out/falling off Dynomax muffler in the stock location.
I had initially pondered going without a muffler, using the dual cats and instead of having a y-pipe after the cats, run dual exhaust to the back. I decided against this plan, and instead simply replaced the cats with mufflers. I went with Moroso spiral flow race mufflers. These mufflers are a bullet style muffler, 4 inches in diameter, and a perfect fit to replace the space occupied by the cats. The install took the better part of the day, and a local shop did a half way decent job. The welds could have been better, but the bends turned out pretty nice, as did the final product. The one downside is I had to go with 2 1/4 inch exhaust, as 2 1/2 inches would have been way too tight. 2 1/4 duals is still better than a single 2 1/2 inch intermediate pipe it replaced.
I knew that these mufflers were going to be loud. I was even afraid that they would be too loud. At idle, as well as at cruising speed, they sound damn good. At about 2,000 rpm's, and under full throttle, they sound like a glasspack system, which I'm not real impressed with. I've pondered whether headers would deepen the sound, or simply make it louder. Another option is going with a Flowmaster muffler, which I almost had gone with initially. The advantage would be a quieter muffler, yet still sound tough. The Moroso mufflers only quiet the exhaust note about 6 db and are basically intended for all out race cars where all you have to have is a muffler in place, with zero regard for noise. The Flowmaster is a dual in/dual out muffler, with the main disadvantage being that with it being a single muffler, running your pipes in/out becomes even tighter.
For now, I'll leave well enough alone. Perhaps down the road, when I do an engine swap, install headers, and change up the rear suspesion creating more room to work, then I'll consider other options. For now, I'm simply happy to have a dual exhaust system in place.