Would I hurt MPG or lose power if I remove the Cat and the downstream oxygen sensor? (1998 Dodge Ram 1500 5.9L)

 

Actually, you will likely GAIN power from removing the cat..... But, leave the rear O2 sensor in there. Just do the non-fouler trick to prevent it from setting a code. (there is a thread about that in the DIY/FAQ section.)

 

Although it is technically illegal to remove federally mandated emissions components, a lot of people do it anyway. You will fail inspection though, if you have them. Don't know if it will do anything for MPG. Is that your goal? Better MPG and more power?

 

In practice you loose MPG, that tail pipe sounds so sweet you cant help but stand off every stop sign

Last cat i had removed was on my 96 cant say i noticed a big improvement overall in the butt dyno. It was significantly louder and cackled more so I ended up with a glass pack to calm it down a hair. Not sure I would do it again but no real reason why or why not.

My current 98 had the cat removed when i bought it, haven't driven it yet since i got it though