I just had a new motor put in my 1986 El Camino 4.3L. The garage that put it in told me that if I put on dual exhaust that it would run better. I don't want to add things that don't make a difference. Any thoughts on this?

Let it breath with 2.5 dauls. better mil. and performance

A free flowing exhaust has several benefits. By reducing pumping losses (energy used to push exhaust out) you free up more power for other things (passing, burning rubber). It can also increase exhaust valve life. A couple of caveats though. If you reduce the back pressure a lot, you will have to richen up a bit. Also, make sure that your exhaust doesn't pass too close to the oil pan (Buick V6), and make sure you still have edequate clearance in the appropriate places.

Dave,
One thing to keep in mind is if you have emissions inspection where you live. In order to pass and have duals, you'll need a couple of high flow catyltic converters. I've read where the horsepower cost is very little with these. Just a thought.