98 - 12valve. Is it worth the money to go to a 4 inch exhaust??? What can I expect in the way of power? Economy? Performance? thank you

 

Cat back ??

I don't know if you're going to do yourself any favors by going from the cat back. If I were going to do it, I'd replace the entire exhaust system including the downpipe ( loose the cat ) and do the entire system in 4". Of course I'd use an Aero.

 

I believe here in colorado we have to keep the converter. What kind of performance / mileage difference did you find when you did your conversion?

 

I kept my stock 3.5" downpipe and used the same 3.5" Aero. I didn't have a cat, I had a resonator. The truck sounds awesome.

 

Most lose MPG going to bigger pipes

 

Why would you lose mpg by going to larger pipes? I would think you would get better MPG by having it run and breathing better?

 

Mostly it is because the turbo does require some back pressure to perform correctly.