Trenthonda1

I wanna run true dual exhaust on my 99 f150 5.4 v8 4x4. I want either magna flow or flowmaster exhaust. Should I leave the stock cats on your cut em off. Also how many cats do I have 2?

Georgia FX4

I'm assuming you don't have any type of emissions testing in your area. With that being said you won't see that much in gains from removing your cats. Most people see minimal gains with an aftermarket exhaust unless you have some kind of forced induction. Look at getting some high flow cats so you can still be legal and get more gains from your set up.

curtk69

if you run no cats on a 97-03 and get a check engine light[cel] does it affect your airfuel ratio? what about a 5.4 l 04-08?