Right. I understood. I was just saying that 2.5" duals on a V8 originally equipped and tuned for single exhaust is enough loss of backpressure to loose any benefit of exhaust scavenging that helps low end torque. So I wouldn't think you'd want to do that to a V6. It may have some effect on high rpm, WOT performance, but how much time do you spend driving at WOT? Off the line and midrange power is much more useable for a street car.
So what I'm thinking is, the best route would be to go with maybe 2", and be sure there is a crossover, maybe in the form of a single free-flowing cat designed for this purpose. If you want the beefy look, just have them put some 2.5" resonator tips on it, it'll look tough and have that echo to it. Most people don't realize that the crossover is very important, and is figured into the tuning of the flow of stock configured engines. Without it, they suffer a lot in the bottom end.
At any rate, I don't know what you have on the intake end, but if you open up the exhaust, you gotta be able to flow more in the front to get much benefit from it. Otherwise you are just creating a "pressure bias" in the overall system, and that doesn't do anything, except waste gas and sound better than it runs.
My friend has a Ford Contour, with the V6, quite overpowered, really, for that size of car. It ran pretty good, and had great throttle response. He wanted to hang duals on it. I gave him this speech, and of course, he didn't listen. Now he hates it. It's loud and obnoxious, slow to pick up from a start, throttle response is rubbery, and his mileage sucks.
