Well, I screwed up my catback installation and thought I'd share my experience while also seeing if anyone had anything to add before I get my X-pipe back with the flange fixed so I can put it on (hopefully the right way this time.

I put everything together and started the car. Nothing sounded wrong but I panicked after the install was done and got paranoid I did something wrong. I'm pretty sure now it was (maybe with a slight exhaust leak), but I noticed a few things:

1. When I looked down I saw that the driver's side looked… not on all the way. The videos I watched didn't actually show a top view of the flange, so when I saw the driver's side spaced out and the passenger's side flush, I assumed the driver's side was also supposed to be flush. I later learned that this is not the case as the flanges are different for each side, but not before I took a hammer to try to maybe straighten the flange on the pipe and move it up so I could get it to sit properly... didn't work obviously, but I was panicking at this point. I took a picture and sent to a helpful Facebook friend (shoutout to Ciro Papi, he is a vendor here, Corvette Exhaust Systems) and he mentioned...
2. … that the flange looked bent. And it was, after looking from the top. That was clearly not a good thing. Also…
3. … one nut/washer were flush and the other nut was crooked. I used nut/washer combos because I couldn't find new M10 flange nuts at Ace Hardware, but have since found them at Lowe's for my second attempt.

I don't have a picture of when the nuts were tight, so it may have been on the donut all of the way.

Mistakes

Further, Ciro asked if I remembered my new gaskets. Uh… what gaskets? At this point I tore everything down, bought gaskets and new/better (grade 10 vs 8) flange nuts, and dropped my X pipe off to the mechanic to get the flange repaired or replaced so I can try this again with a new OEM driver's gasket, new gaskets, and hopefully a complete understanding of what went wrong.

So here's my list so far of what I did wrong and need to do better this weekend when I hopefully get this finally finished:


Flange Installation

What may seem common to someone used to working on cars is that for something like a flange, you want to tighten down one side a little bit at a time instead of one all the way and then another. I thought I was being conscious of this but I may have been careless and tightened one side too much, too quickly. I have to be careful doing this again with a loose hanging flange like this driver's side to do a little at a time per side before the final torque.



Flange Torque

In Serhan's Garage's video on YouTube, he mentioned a torque spec of 35 lb*ft. I did this and my mechanic was telling me that honestly, he just snugs these down when he does them. Going from the bottom with a bunch of extensions and using this torque spec might have been too much and that's why the flange bent. I need to be careful not to over tighten as this flange can apparently be bent without even using impact.



Gaskets

Something that was not mentioned in the videos I was watching for instruction was that both connection points from the catalytic converters to the catback pipes have gaskets. The driver side is a "donut" style and the Passengers side is a thin piece of metal that sits between the two flanges. The donut on my car was there, but pretty beat looking and one should take the time to replace it if already taking this pipe off anyway. However for whatever reason, when I assembled the passenger side, there was no gasket there. Either it fell off and I didn't find it on the floor of the garage or my exhaust has been off before and there was no gasket out back on. Either way, I'm glad I had to take everything back apart because I could replace the driver's side donut and rectify what probably would have been an exhaust leak on the passenger side.




V-Band, Nylon Nuts, and Impact

V-Band clamps use nylon nuts. You should never impact nylon nuts because this will spin them very fast and heat up the nylon, and it may stop doing its job correctly and may leave you stuck with a v band that you can't get off. Apparently not a fun situation to be in. Use hand tools on v bands even though it takes FOREVER to fully tighten them. I luckily didn't overdo it, but I need to do this by hand on the second attempt.

 

My mistakes/learnings:

• Bought a cheap kit (holley). It was so terrible i thought it was used, but it couldn't be, it has metal shavings still fresh in the exhaust. By contrast 2m fab headers came in professional looking.
• Made the same flange error as you but mine was due to the connector bolts not lining up to the CATs. Again poor design
• i continue to have exhaust flap stuck open causing check engine lights. I've changed the actuators, no dice. I've added spaces, no dice.
• I also had a horrible sounding exhaust, turns out 1 side flap was not properly connected.
• My driver side exhaust started leaking, I did not think much of the smoke rising from the rear hatch until i did an inspection and saw the airbox had melted. Whoops.
  • The cause of this was the flange was not properly seated. Why? Because it did not fit properly. Do not buy cheap chit.
• It's REALLY hard to install exhausts without a full lift. be warned.
• Save yourself the headache and remove as much of the body panels you might require for access

 

My 2M Fab catback was $1400 with two pairs of simulators. If you don't care about keeping valves, it's not hard to find $2k or less, doesn't mean they'll be trash necessarily. I'm surprised the Holley was a bad quality system...

I'm hoping they line up properly once my mechanic fixes or replaces the flange... I don't think that was the issue, and honestly I <i>might</i> have had it on properly and just panicked... but again, no pass side gasket, so I would have probably had a leak anyway.

Ouch... I luckily don't have to worry about either pair of actuators or a relearn procedure. I already started the car with the exhaust on and no CELs. The simulators all work, or at least seem to because no immediate CEL.

I was happy with the cold start and idle, but am curious to see how the 2M Fab handles V4 mode, acceleration, and highway driving. I've had nothing but loud cars in the past so I'll probably be happy with it.

I plan to run it in the garage and do everything I can to check for leaks before I put the bumper back on... going to ask mechanic how to check for exhaust leaks tomorrow when I pick up my fixed X pipe.

Warned? I was already done with the bumper back on before I realized it was leaking lol, I've already taken videos of how to get to all 5 nuts and my second time taking the bumper off was actually easy, minus a stubborn electrical connector I did myself a favor and took a video removing the second time around. I made a checklist of all of the torx and 7mm screws/bolts and the 10mm nuts (which are being replaced by wing nuts!!!), and it took me probably 20 minutes with an electric ratchet and a handle of vodka (because I was so pissed off I had to take the bumper off again, but don't work on cars drunk folks, you will wind up with a hammer in hand and not remembering why...). I'm absolutely ready with my extensions and ratchets to get this X pipe on tomorrow evening, already told my boss I'm taking a half day.

The fender liner peeled back and bumper off along with the panel in the trunk removed of course seems to be enough. Paragon made a video in which they reach over the axle and past the shock to get the bottom pass side M8 flange nut from that side, but it's hard without the fender liner entirely off. I may try tomorrow but I also have my own technique for that bolt. I use a ratchet with a ton of extensions and go from the left side of the pipe, reach my right arm around the right side of the pipe and align the socket and ensure it stays on while turning the ratchet with my left hand. The top two on both sides are easily accessible from the top on aftermarket exhaust because it doesn't have those bulky heat shields the factory exhaust has which severely limit ratchets from getting in there unless they have small heads.

 

I've heard those 2m catback in person. They sound pretty darn good.