[dannimo]

I have a stock '98 Chevy Silverado with a 350 Vortech. I want to run true duel exhaust on it. It already has two cats stock. It am planning on putting two Flowmaster "Super 40's" (One of Flowmaster's new mufflers,not the regular 40's nor delta flow). Why does Flowmaster recommend a h-pipe on all duel exhaust. Is there noticable power gains with a h-pipe as opposed to true duels? Isn't that the point of having duels is to separate the exhaust?

[DoubleVision]

a H pipe is there to balance out the pressure and equalize the flow between the 2 sides, this helps low end torque and helps the exhaust to sound better, a true dual system with no balance pipe the exhuast note can be out of phase with the other side and won`t sound good at all.

[astroracer]

Read this Car Craft article... the last couple paragraphs tell the tale.
http://www.carcraft.com/techarticles/69238/
The X pipe system made 2 more horsepower then open headers and was 12 better then the H pipe.
I am looking for another article Car Craft did that compared a "big single" exhaust to your "true duals" setup. The big single made more lowend torque and got better mileage.
True duals are not what you want.
Here is another article that covers headers but the bigger is not always better theory still applies... http://www.carcraft.com/techarticles/116_0312_test/
If you want to get some sound out of your '98 just pull the existing muffler off and put a pipe in it's place. It won't be true duals but it'll sound good and it won't cost an arm and a leg or any lowend torque.