Catalytic converter dump

[spud]

So 1999 4x4 EXP with 4.6 V8

I was told these things have 4 cats on them 2 per side then go into a muffler then out to a single exhaust.

I can I or can I have the exhaust come down, become a single, go through like a single magnaflow or flowmaster CAT then through a single magnaflow of flowmaster muffler and out a single pipe, say 2 1/2" all the way out total and not toss a code? And if its gonna toss a code whats this going to do MPG wise? Also what is the difference in the 4.6 exhaust and the 5.4 exhaust? I see magnaflow offers a direct fit but says for 5.4

To me 4 cats on a 2 into 1 exhaust is about the most ignorant design for an exhaust ever.

I hell my Impala SS only had 2 cats on true dual exhaust from the factory.

 

[FordandPolaris]

Well the idea is to pass emissions... The main problem I see with this is that there are two O2 sensors on each pipe coming from the manifolds. One before each set of cats and one after. You need to keep the two upstream as they help the engine tune the air/fuel mixture. The ones downstream are not important for engine purposes, but if they are not present, it will throw a code because it does not detect the cats doing their job.

A common thing to do with these trucks is cut out the two bigger cats, and leave the smaller ones upstream intact. This allows everything to operate normally, and the downstream O2's detect some change, so it does not throw a light. The upstream cats are very small so essentially you'd run with no cats and a muffler.

If you're going through the trouble of replacing pipe, I'd go with 3in pipe, but that's just me. I like a little deeper sound.

 

[1997SCEBFEX]

agree w/ F&P's write up.
emissions are the factor; not sure if your locale has that test.
i've replaced the 4 sensors on mine, but didn't mess w/ the exhaust except for a Flowmaster 40 series and a 3" exit from the muffler back.

PanHandler.