Do I need to modify the cat?
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Mountain Pass
Joined: May 2003
Posts: 107
Likes: 1
Do I need to modify the cat?
I just received my Gibson cat-back system and was wondering if, while I have the exhaust apart, I should drill any holes or gut some of the inside to the cat. I read elsewhere on here that the cat is a high-flow type. I won't gut it completely because that would create a howl at a certain rpm. I could drill a couple of large holes through the platinum grill and suck it out with a shop vac. The Gibson muffler is a straight-pass type so any leftovers would just blow right out. I will test fit the pipes and weld all joints so it looks good,( clamps look crappy to me). Any ideas?
Fleet Mechanic
Joined: Sep 2002
Posts: 1,769
Likes: 7
From: Gretna ,LA.
The stock cat when cold is straight thru design w/screens being the only visible restriction,now ive been told that when it is hot the catylitic material inside swells up and restricts.You could always disect it, cut it open, do some surgery and put it back together.I thought the clamps were good ones stainless steel,at least on my 2000 model.
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Mountain Pass
Joined: May 2003
Posts: 107
Likes: 1
No the clamps that came with the kit were cheap steel which will rust and look awful after a few cycles. I need to get the dust off the mig anyway (I want and excuse to weld something). I can put an extention on a spade bit and drill a couple of holes all the way through inside maybe. I don't want to take the cat out to do this either.
Senior User
Joined: Feb 2004
Posts: 494
Likes: 14
From: Somewhere west of Arizona
I think I'd just leave the cat alone. Once you start drilling and hacking away in that thing, then the remainder will probably start breaking itself apart while driving. Once they start breaking apart, then the remaining pieces will lodge and plug. The 460's were notorious for eating cats for lunch. A piece would break off, rattle for a few weeks, then turn sideways and plug the cat. Truck won't run with a plugged cat. Besides, your state exempt from smog laws?
If you do decide to drill it, wear a respirator!!!!
If you do decide to drill it, wear a respirator!!!!
Thread Starter
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Mountain Pass
Joined: May 2003
Posts: 107
Likes: 1
You have a good point about the cat slowly coming apart. I'll have to consider it further. I can't wait to hear how the truck will sound after putting everthing in. I wonder if you can unbolt the cat pipe from the muffler and take all the exhaust/muffler assemble out together, or is it too hard? I might want to go back to it one day down the road.
Senior User
Joined: Feb 2004
Posts: 494
Likes: 14
From: Somewhere west of Arizona
Uhhhh, here's a thought.....While you've got everything out, why don't you just remove the cat and add in a section of 3" diameter "test pipe" just to see what it would run like without the cat. Of course, this would be for "off road use only / never to be used on the highway" wink wink
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Mountain Pass
Joined: May 2003
Posts: 107
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I would like to get the BBk 65 mm throttle body next but I haven't benn convinced that it's worth the money yet. Has anyone just replaced the throttle body alone and test drove it afterward? I get the feeling that since I've put in the K&N intake and Granatelli that I need to beef up more downstream components.
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Fleet Mechanic
Joined: Sep 2002
Posts: 1,769
Likes: 7
From: Gretna ,LA.
on my 2000, the cat bolted to the y-pipe with a flange,, then clamped to the pipe going to the muffler, i think just the front part of the muffler is clamped, the back part is welded.Its been so long ago.
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Mountain Pass
Joined: May 2003
Posts: 107
Likes: 1
I plan on keeping this truck for awhile and don't want to really screw things up with the emissions. And also want it to look near stock also. That is a good thought though you have, but wouldn't that really make it louder than before?
Fleet Mechanic
Joined: Sep 2002
Posts: 1,769
Likes: 7
From: Gretna ,LA.
My bbk is nice, but i installed it after i installed the superchip tuner, so all i know is it ran a lot better with the tuner and even better with the bbk.Running stock manifolds and y-pipe and cat, it may not yield results because the bottleneck is those 3 components i just listed.
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Mountain Pass
Joined: May 2003
Posts: 107
Likes: 1
I wish I had the courage to replace the stock headers with some stainless shorty headers, but I don't have a lift or enough patience right now. I've heard some horror stories about the small header studs that will break off inside the head real easy. In the latest HotRod magazine they show a new style of header bolt that has an allen screw in the end to expand and lock it in place.
Junior User
Joined: Jan 2004
Posts: 96
Likes: 0
I've done three sets of headers for other peoples trucks so far and never had a problem with the studs. They've always just spun out for me. I've also done numerous header installs on mustang 4.6's which is the same arrangement and never had a problem there either. Maybe it's my Snap-on tools that make me lucky!
