Exhaust upgrade: To replace cat or not?

[Dave Sanquenetti]

I consulted a local exhaust shop today that a friend recommended. He has his Jeep Rubicon modded to the gills (CAI, cat back, lift, chip, etc.) and has been to this shop for years.



I am going with a cat back system (flowmaster 40) and duals out the rear. Rather than replace the converter, the shop owner recommended not changing it at all. His opinion is that the size and flow of the OEM catalytic converter is sufficient, and replacing it with a high flow cat would just end up throwing errors. He showed me a couple of displayed converters with cutouts to demonstrate the difference between a high flow and OEM. He also felt it wouldn't be worth changing that much seeing as the truck is an 05 and only has 47,000 on it.



Anyone think its worth replacing the cat for a high flow? A couple extra horses doesn't mean much to me. Now, 5-10 extra HP might be worth it. The y-pipe and high flow cat from random tech is a bit out of my budget for the time being. I'm also not so sure I even want to take the exhaust mod that far. Any suggestions on sizing?



I'm looking for subtle changes with a touch more power. The idea is to replace the exhaust, put in a CAI from Zabteck, and get an Xcal 3 in the next few weeks for hopes to improve fuel economy (as long as I keep my foot out of it ). The shop does have a dyno so I'll have to see how much all this improves performance.

 

[Todd Z]

The cats them selves do sufice...



you can simply remove the BACK cat with no chance of throwing codes...



the R/T pipe is 2.5 inches while the stock is 2.25....



Thats where the RT makes some power from..



Todd Z

 

[Dave Sanquenetti]

Thanks Todd! I'll get the bracket back in the mail tomorrow and will be in touch very soon about the CAI.

 

[EddieS'04]

IMO, the '01 to '05 trac has 2 exhaust bottle necks. The muffler with the 2.25 tubing and the pre-cats on the y-pipe. The main converters have a large surface area and fairly large holes in the brick. On the other hand, from my experiance Ford pre-cats have very small holes in the brick. You would have to get a set off jewlers drill bits to size them. I went with a 2.5" cat back on my '04 for 2yrs. When the y-pipe came available, I replaced it. I can definitly tell the difference in performance without a dyno. From 2000rpm to red line. The only reason I would change my main cats, is if they went bad. Or if some reason I was to ever to do alot of long range wide open throttle. Which is not likley,LOL. If your budget will alow, I recomend the Y-pipe to enhance the cat back and CAI. I have ran the y-pipe for 8 months, never thrown a code. Also passed texas emission, houston area, a few months ago.

 

[Rodger Tellefson]

I agree with the above on not changing your cats unless they are bad, and there are 4 of them (2 pre-cats & 2 main cats). You can tell if they are going bad by the sound of a tin can with rocks in it rattling around under neath your ST. Cost me $1200 parts & labor to replace them. FYI, Random Tech does make high flow cats.

 

[FlipTrac_511]

You can tell if they are going bad by the sound of a tin can with rocks in it rattling around under neath your ST.

I hear this after parking my 04; I thought this was normal.

 

[EddieS'04]

Trac, what you are hearing is cool down pinging. What Rodger is talking about is rattling inside the cat from the brick getting loose..

 

[Dave Sanquenetti]

The exhaust is scheduled for replacement on the 28th. The shop owner told me he would not remove any of the cats but place the Flowmaster 40 and the duals out rear for $235.00 aluminized (all 2.25"). He's concerned the computer will throw errors if any of the cats are removed. I just don't want to invest without be able to see some improvement in performance. He told me to expect anywhere between 8-14 extra ponies from this.



Any thoughts?

 

[Dan Long]

The only cat that would cause an error if removed is the first main cat after the y-pipe. I've got all my cats removed and still have no codes, although it might be due to my X-Cal tune. I'm not the original owner of the Xcal, so I'm not sure if they turned off the last O2 sensor or not when they wrote the tunes.