01 Grand Cherokee 4.7L exhaust mods - suggestions?

[jamx13]

The muffler on my 01 Grand Cherokee is split at the seam & needs to be replaced. I'm considering a few different options & I'm hoping for some input. This is the original exhaust & the pipes are in good shape. The muffler has a 2.25" inlet & a 2.5" outlet. The tail pipe is welded to the muffler but I intend to cut it with a sawzall as close as possible - this will leave several inches of straight pipe to allow for a slip joint connection.

If you're familiar with the Y-pipe setup on the 4.7L, there are 2 small cats with O2 sensors before & after each, then a larger 3rd cat downstream. On my system, the inlet on the 3rd cat is 2.5", the outlet is 2.25", but there are no O2 sensors before or after. This leads me to believe the 3rd cat can eliminated without triggering the OBD code/check engine light. Would that be correct? If it is, removing the 3rd cat will allow me to run 2.5" pipe & muffler without the need for any reducers, therefore I would have an easier, cleaner looking installation.

From an emissions standpoint, I'm sure removing the 3rd cat is a no-no, so if I were to leave it in place, I would have 3 options:

1. increase the the pipe size from 2.25" to 2.5" immediately after the cat & install a muffler with 2.5" inlet/outlet

2. install a muffler with 2.25" inlet/outlet immediately after the cat, then increase the the pipe size from 2.25" to 2.5" after the muffler

3. locate a muffler with 2.25" inlet & 2.5" outlet

Any comments or suggestions on which method would be best? Any muffler recommendations? I'm thinking some brand of turbo or possibly a Walker SoundFX, no glasspack. Thanks.

[jamx13]

Well, so much for getting any help or suggestions. If anyone cares, I bought a Dynomax Super Turbo with 2.5" inlet/outlet & went with option 1.

[fredjacksonsan]

Sorry for the delay...not on here much these days.

I'd have gone with option 1 also...continue the same diameter pipe to the back. I'd have also checked with local emission regulations, although things these days run so clean that you probably won't have an issue making emissions with 1 less cat. (Especially since there's no sensors at the 2nd cat)

How is the new exhaust working? Have you noticed any improvement in MPG or power?

[jamx13]

I haven't checked the mileage yet but I do like the sound of the muffler - nice deep rumble that's not obnoxious. And when you lay into it, it sounds great. I also modified the factory air intake box by by drilling a series of holes with a hole saw in the front & fender side of the box. I didn't do the back or engine side of the box because I assumed the intake air would be warmer in those areas. The holes are staggered so as not to weaken the box, but I managed to drill quite a few of them. I dressed them up with a file when I was done. I should have taken a pic because I think it turned out pretty good. Here's a pic I found doing a google search, it's not of a Jeep air box, but it will give you an idea of what I did:

http://www.norman.pyke.btinternet.co...mod_airbox.jpg

[fredjacksonsan]

That will help it breath....be interested to hear the mpg with the new adds.

[jamx13]

Looks like I picked up about 2 MPG +/-. I got about 15.1 MPG on the last tank full.