I believe that my 95 F150 with the 300 six has clogged one cat and the other is developing a good leak. I want to replace the y pipe with a walker downpipe and then run back to my muffler. The exhaust shop cut the pipe after the second cat and put what I believe to be 3" pipe in, to match the outlet of the cat? I have heard that the walker downpipe is 2.25"? What should I do? Or is the piping from the 2nd cat smaller than that?

 

Usually the 300 has a 2" pipe but it could be a 2.25"

 

Are you talking from the second cat back? Also, I know that the truck has air injection for the cat, I can't just cap that off and if I leave it hanging it will give that classic tick/woosh noise. Could I drill and weld a little pipe to fit that and put that in the y pipe?

 

Usually the entire system on the 300s are 2" or 2.25" max yes. The only way I can see the second cat having a 3" outlet is if it has already been changed or they made an adaptor. The easy way would be to measure the tailpipe, you could also take a tape and eyeball it to get a rough idea of what size it is between the cats and at the headerpipe.

 

Went out and looked, its not 3" thats for sure, as for the air injection, would putting a fitting in the pipe downstream of the O2 sensor take care of the woosh/tick and still keep the air pump working?

 

Yea, you can weld in the air tube in the pipe...just remember after the o2

 

In welding the air injection pipe into the y pipe after the O2 sensor, will this make my exhaust have an odd sound, or will that be lost to the no cats and flo-pro muffler?

 

you wont hear anything