So I called the muffler shop to get an estimate on them installing a muffler and two high flow cats. Well, the guy tells me that I need 4 high flow cats because there are 4 o2 sensors, so it would be illegal for me to do just the two. Well I know you can do the two but I need help to explain to the guy why I only need two. So if someone could help me with that. The trucks an 02.

 

u dont need four cats, if u get highflows you only use two, thats the whole idea is havin just the two and not four. you position them between the two sensors on each side.
Scott

 

I Have 2 high flows, all 4 sensors, no problems. Got that done for 140 including magnaflow high flows

 

So how would you reccommend me explaining it to them? What I said was that the two high flows take the place of the 4 cats and that you place the o2 sensors on the new high flows. Built where were all your sensors placed?

 

Find a different shop that's willing to risk EPA scrutiny. What you want to do is technically illegal.

 

if its like my 98 there should be two sensors on each side with one before the 2 cats and one after, i didnt think there was on in them or did they change the newer ones. but if its like mine he just needs to cut the old cats and and weld the new ones in with a little extra pipe inbetween the two sensors on each side.
Scott

 

Yes a lot of shops will not even touch the cats for that reason. They could get a big fine or loos there license.
You may have to look around for someone to do it.
Good luck,it's a great mod!!!

Phil

 

So should I just telll him that the one set of o2 sensors are in the manifold and the second set will go behind the hi flows in the exhaust pipe?

 

well basically yes, but the first set of o2 sensors are just after the manifolds, but other than that youve got it.

 

Do you get much sound on a 2v 5.4 doing a setup like this? What is the main reason behind this mod?

 

Got mine done today. All four were shot. Had 2 high flows (one on each side,magna flow).
Also had a flowmaster 40 installed. Sounds great!
Definetly not loud. Just throaty at take off. Stepping on the gas and downshifting is nice, not loud.
Sensors were put back in. No CEL on.

 

I put a true dual set up on my truck with Flowmaster 40s and it sounded good but later when I went with a set of bassani high flow cats it was at least 3 times as loud.

Phil