Decided to gut my pup cats today and it was a breeze using just simple tools.

1. Unbolt H-pipe from muffler assembly
2. Remove rear hangar bracket lower bolts (on front of tranny). They're the ones that have the springs.
3. Remove the O2 sensors from just behind the main cats. It's a good idea to remove several inches of the wire from the clips on the heat shield to minimize twisting of the wire.
4. Remove the nuts that attach the exhaust to the header outlet. At this point the only thing holding the exhaust up is the front bracket where the exhaust bolts to the bell housing forward of the main cats.

I did this alone with the car raised just enough to fit under it as I do not have a lift.

5. Position your knees near the center of the whole assy. so you can use your legs to lower it when you remove the last 2 bolts (on the front hangar bracket) Once these are out you can lower the whole assy and slide it out from under the car.

6. Position the assy. on a stand or somewhere that you can have the pre-cats at the lowest point (to prevent debris from falling into the main cats)

7. Using a large straight slot screwdriver simply dig the catalyst material out of the bubbled portion of the pipe (it comes out fairly easy) Once you have the bulk of it out you'll have to fabricate a tool to scrape out the insulation that lines the bubble. (THIS INSULATION MIGHT BE ASBESTOS...WEAR A DUST MASK OR RESPIRATOR, OR DO IT OUTSIDE IF THERE IS A BREEZE TO KEEP FROM INHALING THE DUST!!!!!) I made a scraper out of an old steel ruler with a 1 inch 90 degree bend on one end to scrape out the remainder. You will need this tool to reach around the slight corner to ensure you get out all of the insulation.

8. Using a leaf blower, blow out the pipe from the exhaust end to ensure all material is removed to avoid fouling the main cats.

9. Re-install the exhaust in revers order of removal. Use anti-sieze compound on everything with threads and be careful when re-installing the O2 sensors. Put them in the hole and screw them backwards (not in) to pre-twist the wire (about 3 turns should do) then screw them in.

Whole project including raising and lowering the car was approx 3 hours. The car has a slightly more aggressive exhaust note and is noticeably louder at WOT, probably like what an 02 model sounds like and GM claims 5 additional HP with them removed.

My car has always felt very strong so I didn't notice any difference in SOTP but I recieved my MAF Translator today so once I get it wired I'll have to get a scanner to see where my fuel trims are. then off to the dyno. I think with the pups gone, my T1 intake and then dial in the fuel trims with the MAFT I should be in the 400+ HP range. All for under $1000.

If anyone needs the torque values for all of the bolts...let me know and I'll post them.

 

Your going to jail :nono: :nono: :nono:

 

Very nice description. I've been thinking about doing this to mine... So, what are the torque specs for the bolts?

 

Here are some pics of the removal of my pre-cats

 

Torque specs.......

All bolts are to be tightened to 37 lb/ft

Except the following:

Exhaust flange to header outlet.....15 lb/ft
O2 sensor.................................. .....30 lb/ft

Note: The rear hangar bracket (the one with the springs) calls for 37 lb/ft also but using this torque is enough to twist the bracket where it's welded to the exhaust pipe. 25-30 lb/ft should be plenty tight.

 

Great. Thanks for the info... :cheers:

 

If/When you perform this mod be sure to REMOVE ALL OF THE INSULATION!! There is quite a bit there. If you don't take your time & remove it all, clogging or partial clogging of both or one of the main cats will be the result. Not good!! In addition to blowing the assembly out from the other end with a leaf blower, it's a very good idea to use a good vaccume cleaner with the flexible hose attachment to 'suck out' small insulation particles & dust while you are scrapping & cleaning. Picking up the entire assembly and shaking it out (frequently) also helps. Don't forget to use a respirator because inhaling this dust is certainly a no-no!!

Also, when starting to break up & remove the main material, it's a very good idea to not use a sharp pointed standard screwdriver. Use a large 'phillips' head instead. This will keep from possibly punching a hole in the pup cat by accident. Also not good. The material isn't that hard & should break up fairly easily.

I can email a picture of the tool that you should use in order to completely remove/scrape the inside of the gutted 'pup' clean of insulation for anyone that's interested.

Take your time & be patient. The car will sound better & will certainly breath better!! :yesnod: :yesnod:

 

I gutted last weekend, and it took HOURS to get all the insulation/whatever out of the pup. Picking and tapping with a hammer and vacuuming and pick, pick, pick. I made several different shaped pick tools by flattening the ends of coathanger wire, and used a piece of hacksaw blade, too. And, after many hours of very careful work, including blowing out from the other end and hanging the pipes vertically (down) and tapping to remove any junk that may have made it to the main cats, I could STILL get little bits of stuff out of that internal flange area. What a PIA.

But, the exhaust note did change (deeper, a touch louder, more crackle), and there might be a bit more "perk" in the motor, so it was a good, free mod. But the Sawzall and welding in new pipe approach is probably better. Less chance of getting some junk in your main cats, which would be VERY bad.

 

Ditto that! It did not take me hours but I had to be patient and get it all. I used a piece of old aluminum trim that they used to use around countertops and bent it to go into the pipe and scrape the sides. I sharpened one side.

The leaf blower is a good idea! ;) I turned the pipes upside down and then vacuumed - REPEATEDLY! :crazy: