catalytic converter placements

[RootBreaker]

ok so i cant get my truck through inspection whatso ever..

failed emmissions 6 times..and im not barely failing..

allowed ppm is 300 and im at 1550!!!!!

so my uncle checked my timing (right on)
set my air/fuel screws (not sure how off they were but not much)
checked my vacuum (19 while idle)

he said i should be set right.. and said sometimes when you cam/modify you wont pass no matter what... so he set it or california emmissions.. 6 degree timing..


he then kicked me a set of cats and said.. put these on...

now here is my question.. I dont NEED cats... but will put them on to get through inspection... but i need to know..

will a cat perform the same behind the muffler instead of in front?

my exhaust dumps under the bed (totally legal... exhaust must be 12" beyond a open sitting area).. so i could just shuck the cats on the back of it... and be done...


but if it was said that no.. cats work best closer to the motor in front of the muffler.. id have to cut the exhaust and work it all over and get them in there and they wont be that easy to get out if I do pass...


if the truck does not pass.. it WILL get a 2005ish 6.0L

 

[80' 427]

Well on med duty trucks it used to be muffler then cat. Of course they are worked hard and have lots of exhaust temp. They really need to be close to the head for best light off.

Could you just make test pipes to replace the converters when not testing?

 

[Blue85]

I've always put them on the underside of the vehicle

The closer to the headers, the better. If you have header flanges or a bolt-in crossover pipe, you could have a flange added and make removable cat(s). You would have straight pipes made to the same length with the same flanges. But you will spend extra coin on all these parts. If you can live with the reduction of sound, why not just leave the cat(s) in?