So, I finally got the cats removed. Replaced with straight 2.5" pipe.

My lord, I *hate* the way it sounds right now. The truck used to sound awesome -- nice flowmaster rumble. Now its raspy (see below) and raw sounding, not to mention there is so much added in cab resonance that sometimes you can't hear to talk on the phone or hear the radio if its less than 1/2 way up.

I think I might have an exhaust leak as well. I've lost 3 psi from the turbo and it spins up like a dog. Where as I used to get almost instant boost, now, it starts at 0 and slowly craws to 4 psi regardless of RPM range.

I'm gonna call Dave as soon as he wakes up and see if removing the cats should change the flow characteristics of the exhaust that much (I don't think so, but hey, remote mounts are new). If he says no, I'm back to the shop that did the swap for some exhaust leak repairs.

 

The sound I can vouch for as being CRAP!!

The concern I have is your boost loss and lag. Are you sure you don't have a bad exhaust leak?? I just found one on my truck on the driverside manifold collector and am wondering how much this will effect spool time. Maybe that is part of the reason I am lagging so bad. Maybe you could try to fix the exhaust leak if you find one first and see if things change. I thought Rick (Hawk179) tried with and without cats and found it to spool faster without them. If it spools better with them then I'm buying a new set of pipes!!

Please keep us updated Erik.

 

Well, that sucks and really doesn't make sense when you think about it. Doesn't seem like an exhaust would have a huge impact, unless it was significant.

 

Any chance the guys intentionally/unintentinally monkeyed around with the turbo setup out back in order to get the pipes off the manifolds/headers on and off the cat-back section?

Maybe something got bumped or shaken loose.

 

I would put the catalytic converters back in place or find an aftermarket brand of converter that you feel comfortable with. That drone and rasp that you hear so much about, is from an improperly designed and tuned exhaust system.Even some aftermarket ones will do that. That's the challenge of designing an exhaust system. Exhaust systems are heat and sound frequency interrelated. Plus you have a closed system that pulses as each valve opens and closes. The OEM manufactures do alot of testing to reduce noise levels when they sell a car. So everything is tuned for the cats in place. There are alot of very powerful cars that have catalytic converters in place, so you're not really giving up anything by remving it. You can tune in a different way to compensate for having them. The turbo usually will quiet some things down, so you can usually get away with a louder muffler. Hmmmmm...

 

I also notice my truck getting louder after removing the cats.

 

I gutted mine and it got louder, but it's a good loud. Love the way it sounds. May sound different without my muffler and the turbo in place though.

 

I expected louder. I wanted louder

I really think there's a leak due to the falloff in boost (makes a lot more sense than increasing the flow of the exhaust = increased lag and lower boost).

 

It's a matter of backpressure. Without the catalytic converters there is less backpressure which means the exhaust is less dense and less able to do work.

 

The turbo itself is gonna create ALOT more backpressure that the cats could EVER produce, I think there is an exhaust leak somewhere......