Alrighty, here it goes. I was looking under my truck today because I was thinking of replacing the stock cats with some high flow's or just taking the back cats off and running just fronts. However, once I looked at the stock cats my head started spinning. They are very, very rusted! Does anyone know if the 45 degree cat is welded right to the back cat? Also, if I could just SOMEHOW get the 2 apart...would it be o.k. to run just the front cats? I would just take it to a muffler shop and be like "Here is a set of High-Flow cats...now, just take of the old ones and put on the new!" with a big grin on my face but I dont feel like paying $9,999,999,999,999 just for that! Thanks for the info!

 

Cut them all off, the little precats will not "treat" the exhaust enough, and unless you have MIL eliminators, they will set a inefficency code. It would be best to just dump all four and get the high flows, it shouldn't cost very much, with a sawzaw and a little work they will all come off fine.

 

Yea they will josh , I ran that set up for awhile. Your still within parameters running with just the fronts. You won't need eliminators. Not on the 97-98 5.4L' s anyway. Mine ran great with the stock tune and had better mileage with that configuration. You ever look inside the forward cats ? There definitely not lacking.

BUT - The 99 + 5.4L's and 01 + 4.6L's have PI heads that flow more. I'm not sure about those. You might get the inefficiency codes as stated (PO420 and PO430 codes)



BTW - That set up sounds Bad A$$ on these older models IMO - Sounds close to older GT's under normal acceleration. Better than it does with LT's w/stock tune that I'm running currently. I need a tune now .. Also, when I ran with just the forward cats , I was running a Flowmaster 50 series muffler (not the SUV style 50, the HP 50). I then swapped the Flowmaster with a Magnaflow 22" straight thru muffler. She was quicker off the line with the Magnaflow, but honestly, the Flowmaster sounded better. Guess you can't have everything.

 

It would also depend on mileage, If the vehicle is high miles, the likelyhood of the precats being "enough" is reduced. But it's your choice OP, I like the idea of only 2 high flows. Jbrew, I wish you had a vid. of the setup, I had thought about doing this and would of liked to hear the noise.

 

I wish I did too.. I miss that sound. It's funny . as old as those cats were , they looked real good inside.

Hard to explain how it sounded exactly , it sounded best taking from the light normally - low r's , from idle on up if you know what I mean. - Like the older GT's sounded. You know how that gt sounded , you could tell it was a Mustang GT without even seeing it. Well, that's what it reminded me of - I liked it

Should of never F'ed with it..:o

 

yea, as of right now it has 120,133 miles. I think I might try cuttin off the back two for now until I get some high flows. With the high flows, do they replace all 4 of the stock cats?

 

2 high flows replace 4 stock cats!

Phil

 

do the high flows you will love them.

 

What did you end up doing Wrathchild375? I added a new thread on my high flow installation. I'm having problems right now. See this thread https://www.f150online.com/forums/sh...d.php?t=326690 if anyone can help.