Hey guys, Need your help.

I have a 99 Expy, and I am going to redo the exhuast. I bought Headers from summit becuase I cracked an exhaust manifold..

So I was thinking about replacing the cats too. I was gonna order them all from Summit, but I got a little confused.

I will end up going with the Mangaflow High flow cat

Catalytic Converter; 91000 Series Small Oval; OBDII Compliant Universal Catalytic Converter; 2.25 in. In/Out O

I would need 2 of these.. but there are 2 precats or what look like precats before the cats.

So i guess the cats from Magnaflow are not direct bolt on replacement.. I would have to weld these into place right and probably either make a new pipe going up to the headers or weld them into the pre cats right?

Any help would be greatly appreciated.

Thanks

Scott

 

I've heard things about Ford trucks having 4 cats, really confused me, That is probably what you are talking about pre-cats, I would just rip them things out, run the aftermarket headers & the two aftermarket cats and your system

 

Well, I was looking at it, and there are a series of O2 sensors... one up top close to the collector, where the manifold and what I thought was a pre cat is.. and then one more down below on the cat.

I would have no problem getting rid of the upper one if there was a simple way to by pass the O2 sensor....

Just run new pipe from the new header down to the new cat..

Anyone got a good part number for the Left and Right from magnaflow for a 99 4.6 2WD?

 

i would suggest doing the high flow cats from troyer; the stock setup uses four cats total, but with the aftermarket one, you reduce it to one cat per side. after that do something non-restricting for a muffler. im running a 23" glass pack- only $20, and its nice and mellow at idle, but gets quite a bit louder if you romp on it.

 

Well here is my dilemma

There are 4 O2 sensors... so there are 4 cats... even if I run with a high flow cat.. it still has to go through the upper cats... close to the collector. I cannot find any high flow cat to replace these 2.

And if i had to delete them, how would I get by the 02 sensors that are still there? is there some kind of trick component that i could plug into the sensor connector to make it think it was reading the cat??

--Scott