This issue was getting mixed in the other thread.
So I’ll start from the beginning…relevant mods: APR stg 2 tune, Neuspeed cat-back exhaust (so downpipes to tips), stock motor mounts, roc euro intake, 100 octane blend, tracking the car at Mid-Ohio. Unfortunately no logging going on.
At turn 10a, the car started to sound like a 65 mustang. Long story short the cat broke somewhere after the flange that connects the exhaust manifold. I can grab the down pipe on one side and shake it…nothing…the other one clangs around and I can see the cat tube moving relative to the flange. In case you are not familiar with the B8 S4 exhaust, you can see where the cat is here
I called the dealership and they won’t do shit…which is no surprise. I am not the kind of person that will swap all stock parts and pretend like this happened at the taco bell drive through.
Bummer indeed. The root cause is probably one of:
Aftermarket exhaust put too much stress on this joint, which seems unlikely because the downpipes have a flex joint. But it definitely took some finesse to make the tips line up correctly at the valence;
The tune was running lean and heating up the catalyst too much which weakened the pipe. I was running hard at the track so maybe EGT’s just went up naturally and this is what I get. But never heard of another person having this issue;
The motor mounts have failed (which is probably true, they are oil filled and known to fail) and allowed the motor too much translation/rotation which overstressed the cat joint under all the forces imparted by mid-ohio;
The part was poorly manufactured.
Honestly, I have no idea which one is the case.
At this point, I’ve spoken to Ray (who does all the work on Jeff’s car) and he will look into it. Great guy. He advised dropping the whole driveline, based on his experience with Jeff’s header install. I’ve read the cat’s are accessible by dropping the trans and rotating the engine, but honestly, I’m not going to question his thoughts. He thinks this will overall make it easier and quicker. Luckily the Canadian dollar has tanked and he’s in Windsor, unluckily, there is 13% tax. Overall it still works out to a labor rate of around $90/hr.
The plan is then to weld the cat back together. I don’t know. I’m pretty torn on this…Michigan has no smog checks so the smell is probably what will hold me back from test pipes. Keep in mind this is still an every other day DD, plus a car that I might one day sell. I don’t really care about the 20 HP or whatever sound I would gain…BUT fixing the factory cat might just set me up for the same or other issues down the road. Since the tune will probably eventually kill the cats. He will likely reinforce the cat with some splints to strengthen the weld. New cat is 1.1k MSRP.
Ray is a smart enough guy where we will diagnose if the root cause is related to my exhaust. I hope I don’t need to replace the exhaust…would probably go with JHM or Milltek. But again, don’t want this to turn into a 4-5k solution.
Definitely a shitty day when you realize what pay to play really means…but it could have been worse…could have smashed into the guard rail or something. Or blown a motor.