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I wanted to create this post to help anyone wanting to swap out the primary factory downpipes. This would be for people not wanting to do headers because of the tune required. I was searching time after time, trying to find photos on what everyone was talking about (Jack up the engine or remove the studs). These photos will show how to accomplish jacking up the engine and pulling off the stock downpipes.
Loosen the 4 motor mount nuts on the subframe (not all the way off). Use a jack with a thick rubber pad to lift the bottom of the motor, the selected point of the oil pan. You only have to lift the motor about 1/2 inch.
These are the studs coming off the stock manifold downpipe mounting point. You can use a socket to remove these with the engine lifted. BE CAREFUL it is very easy to round off the studs or break them. I recommend leaving the studs in place and reusing the nuts. If you get them out, you can replace them with stainless steel bolts.
Mounting the catless downpipes using the factory studs and nuts.
I used big daddies garage 90 degree adapter for the post cat o2 sensors and do not have a CEL.
I fully wrapped the pipes for heat reduction, especially around the oil cooler (GM engineers to blame). The downpipes used are EOS Catless. Total time to install when jacking the engine with access to a lift. Less than 2 hours.
You do not have to remove the X-Pipe to install the downpipes.
Last edited by Diamondxx; Apr 27, 2024 at 09:07 PM.
did the same mods last yr. when all 4 cats are removed the smell in the cabin is virtually unbearable. sitting at a red light its an instant headache. removed the 2 piece x pipe thinking it was leaking had it welded to a 1 piece. no change . replaced all the new clamps with newer clamps no change. in the end I reinstalled the oem x pipe with the resonators and the smell is no gone completely. when I move to full ethanol ill try to reinstall the eos mid pipe . until then this is a good way to run it without smell and headaches.
did the same mods last yr. when all 4 cats are removed the smell in the cabin is virtually unbearable. sitting at a red light its an instant headache. removed the 2 piece x pipe thinking it was leaking had it welded to a 1 piece. no change . replaced all the new clamps with newer clamps no change. in the end I reinstalled the oem x pipe with the resonators and the smell is no gone completely. when I move to full ethanol ill try to reinstall the eos mid pipe . until then this is a good way to run it without smell and headaches.
Is there any sound or power difference? Hard to tell from video.
Power I can't speak on.
Sound is brutal. Throttle 50% - WOT sounds like a racecar. Its basically a straight piped 6.2L with the benefit of the AWE tips extending further out from the car.
ethanol smell in pump form por ignite 98 is fine. no bother at all. when folks dont want to ride due the headaches and smell that is another issue.
the only time I get a hint is if I'm at a red light with the windows down or in the garage when I start/park.
I was anticipating it to be a lot worse from the way everyone was talking about it, but i guess smell is subjective. My wife doesn't even mind the smell because its so minimal at the red lights.
Thought: I'm wondering if its not as bad because my AWE exhaust tips stick out a good bit further than factory away from the car?
Last edited by Diamondxx; Apr 29, 2024 at 01:11 PM.
Reason: added thought
the only time I get a hint is if I'm at a red light with the windows down or in the garage when I start/park.
I was anticipating it to be a lot worse from the way everyone was talking about it, but i guess smell is subjective. My wife doesn't even mind the smell because its so minimal at the red lights.
Thought: I'm wondering if its not as bad because my AWE exhaust tips stick out a good bit further than factory away from the car?
I guess it's a possibility. all my cars from Mercedes to Porsches Audis and such were all on corn with no cats. never and issue. did this car and first guy I met up with I n his c8 remarked how he could smell the exhaust from his car. even after a street tune with full bolt ons I couldn't stand the headaches and smell. asked the tuner if I could go back to oem mid pipe (easiest to reinstall) and immediately the smell was gone. road trip to Texas 2000 miles since and zero issues. when I go corn ill try catless again
Wish I could do that here in NC. We have emission tests.
yrs ago when I had the porsche we had emissions in tn. on corn it was never an issue to pass. never tried with pump 93. visually you could fake it by gutting the oem cats . no idea about the obd plug in computer they use
I didnt touch the engine mounts, I just removed 3 of the studs on each side usually leaving the top left corner and that was more than enough. May not have been the fastest but overall without dropping one of the nuts in the kmember area i would of had it done in more of a timely manner. Also did mine on quickjacks as well. Also was reusing the O2 sensors and those were in very snug on the stock downpipes and once I had them off the car probably made it more difficult to remove those.
oh yeah the gas smell is strong for sure, enough to make my garage smell for a few hours after its off, lol
Why would you remove the cats in the first place? The hp gains are minimal so that's not a good answer & the rotten egg smell in traffic is awful. If you have emission testing in your area, that's a no no
Why would you remove the cats in the first place? The hp gains are minimal so that's not a good answer & the rotten egg smell in traffic is awful. If you have emission testing in your area, that's a no no
Why would you remove the cats in the first place? The hp gains are minimal so that's not a good answer & the rotten egg smell in traffic is awful. If you have emission testing in your area, that's a no no
There isn't a rotten egg smell - have you smelled a catless LT1 / LT4? The most of it is just a gas like at a gas station smell. I don't attribute that to rotten egg like a clogged cat smell.
I don't get it. Removing cats makes you sick to drive the car, offers zero real world HP gain, reduces resale value of car. Net sum: A lot of work and some $ to make the car a worse driving experience and devalue it. Why? Different strokes, I guess...
I don't get it. Removing cats makes you sick to drive the car, offers zero real world HP gain, reduces resale value of car. Net sum: A lot of work and some $ to make the car a worse driving experience and devalue it. Why? Different strokes, I guess...
Your take is extremely subjective. It's a much better experience for me.
Also, I can swap the cats back on for resale no difference...
[Guide] Downpipe Install - Poor Man Headers
