The exhaust on my 1997 Ram 4x4 is rusty and needing to be replaced. I was thinking of going with an aftermarket hi-flo cat. Is this a good idea or should i get an oem from the local dealership??

 

your on the right path as i would also go with an after market exhaust kit and not a dealer kit , try and go with the 3" kit to unleash some more power unless you live in a state where you need to keep it under control

 

A high flow cat would help out greatly, just make sure to get the right size cat. Another way to help with the flow is to take the Y-pipe to a local exahust shot and have them bend you a new one with smooth bends.

I'd got with a kit that has smooth bends and install a hooker max flow muffler. they flow twice as much as the flowmasters do.

 

I was thinking of going with 3" from the manifolds back.

 

If you do go 3" back then you will lose some backpressure and will lose some low end power. I'd run the standard back to the cat and from the cat back run 3" single if you want.