larger diameter cat connections?
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Senior User
Joined: Oct 2004
Posts: 104
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From: Pearland, TX
larger diameter cat connections?
So.... all these big exhausts are having to go through the cat... 3" pipe at the inlet&outlet. I keep hearing that the cat itself flows great, but there is still the restriction at the connections. So, boundary theory aside, what real benefit is there with larger diameter exhast pre-cat? (more noise?) Does ford make a cat with larger pipe connections? or is there an accepted aftermarket cat for this purpose?
oh- and if your response is to delete the cat, save it.
oh- and if your response is to delete the cat, save it.
Posting Guru
Joined: Jan 2004
Posts: 1,539
Likes: 1
From: Snohomish, Washington
The inlet and outlet is a 3.5 inch diameter. As for the down pipe, it too is 3 to 3.5" depending on the bend. With a 4" downpipe there is less restriction right on the other side of the turbo which helps because there is more room for the exhaust to escape than with the 3.5" downpipe that is stock since it has so many crimped bends. Also, the cat will need to be deleted at some point or replaced because diesels do nothing but collect soot quickly which is the big reason people want to remove them. I left mine on because I could see right through it still. I have also read that you can clean them out by blowing (with air) the stuff it collects if you want to. Never tried it and I find it hard to really believe.
Post Fiend
Joined: Oct 2002
Posts: 11,314
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You can also do what I asked my muffler guy to do....
knowing the the main part of the cat is larger than 4 inches...
On my 03 6.0L X the cat inlet and outlet both flare a LOT...
Have them cut the ends to match up with the inlet pipe and outlet pipe...
the front of the cat was cut large enough to allow the tailpipe to fit INSIDE the cat inlet and then welded....
the rear of the cat was cut to as large an opening as possible but still let the cat fit INSIDE the tailpipe and welded there...
flows pretty well enough for ME
knowing the the main part of the cat is larger than 4 inches...
On my 03 6.0L X the cat inlet and outlet both flare a LOT...
Have them cut the ends to match up with the inlet pipe and outlet pipe...
the front of the cat was cut large enough to allow the tailpipe to fit INSIDE the cat inlet and then welded....
the rear of the cat was cut to as large an opening as possible but still let the cat fit INSIDE the tailpipe and welded there...
flows pretty well enough for ME
Last edited by jdadamsjr; Oct 19, 2004 at 03:14 PM.
Elder User
Joined: May 2003
Posts: 833
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From: NW Montana
I am going back to a state that does not check for such things as emissions equipment. I have an '05 6.0 and am wondering do I really need to keep the cat on? I would prefer to go to the lightly muffled 4" no cat.
Post Fiend
Joined: Oct 2002
Posts: 11,314
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And, in case you didn't realize it, it is a FEDERAL law regarding tampering with the emissions so the state you go to may not "test" for that, but you can still be ticketed!
and like stated b4, many have seen little or no difference with performance or fuelage...
And, OBTW, other sites won't even allow you to discuss this since it is illegal
so the state you go to may not "test" for that, but you can still be ticketed!and like stated b4, many have seen little or no difference with performance or fuelage...
And, OBTW, other sites won't even allow you to discuss this since it is illegal
