I had the loudmouth modular catback put on over a year ago and loved the sound. I've since put on my pacesetter lts and a texas speed ory, but the car was ridiculously loud and raspy with the loudmouth resonator so I put a magnaflow straight through muffler on it which has quieted it down a bit but it still really raspy especially when downshifting. Another thing I noticed is that I seemed to have lost alot of low end power. A couple of guys at my job said that by getting rid of the cats and having no restrictions, you lose backpressure and low end power as well as having alot of drone/rasp. I'm also noticing that when I step on the gas and let off around 2500 rpm there's like a coughing/crunching sound underneath the car which wasn't present before. I had all the work done at an exhaust shop, and from underneath there doesn't appear to be any leaks. I'm almost ready to put some cats on there cuz the car is running and sounding like sh*t. An ASE master certified mechanic also told me that the rear O2 sensors do more than just tell the PCM that the cats are working which is contrary to what people have said on here.. They are both responsible for monitoring air fuel ratios and adjusting long term fuel trims, which makes sense because my car is also running very poorly since removing the rear O2s.. Any advice you guys could give me would be appreciated.. thanks..

 

Well, the ASE Master Certified Garunteed Super Duper Mechanic is wrong on this one.

I'd bet money the lack of power is either due to something not buttoned up right (ie plugs, wires, loose ground, etc.), your AFR being off, or knock retard. I had a stock-internals motor running through a free-flowing set of 3" true duals (even less backpressure than your system) and when I switched to a Magnaflow catback, it slowed down some. Your torque curve might move around a little, but I have yet to see any physical proof of less backpressure equaling a slower car. Even my buddies big-block T/A runs better with open headers at the track.

Chances are, you're running too lean and possibly causing some knock. Then, the knock sensors are picking up the pinging sound and pulling timing. Get your car tuned for your setup or better yet, buy some software & a WBO2 and tune it yourself. Then, tell your mechanic how wrong he was about the stock rear O2's contribution to the LTFT's.

 

I had rasp around 2500/2600 rpm's with kooks lt's and kooks ory w/ no cats. no I have true duals, x-pipe w/ bullets dumped. no rasp but, alot of lope.



fuerzaws6

 

I agree, the mechanic is wrong. Now I would give it a few days, about 200-250 miles for the computer to relearn itself before you get worried. Although I would check for loose connections and stuff.

 

Did you install some 02 sims or have your rear 02's deleted from your PCM. If you just put them back into the ORY pipe then that be your problem.

 

I've checked all the plugs, wires, etc. Theres no loose connections. I used some high quality band clamps and there's no trace of carbon/soot at any of the joints. I haven't had the car tuned yet, I just got rid of the rear O2s since theres no place to put them with the ORY setup. I haven't had time to fully go in and pull out the AIR pump system since they are race style headers, I just pulled out the relay so it wouldn't turn on. I know I am going to need a tune, im just wondering if a tune is going to solve these issues I am having. I am eventually planning on getting a cam, so I really dont want to have to pay a few hundred bucks all over again after getting the cam installed. I just want my car to run decent in the meantime.

 

Yeah, I believe the power distribution has moved the the upper range, not disappeared, but that's why I a drive a transam is for low end power, not for high end otherwise I would be driving a ricer. What would be causing me to run lean? And would vibration from the ypipe hitting the floor panel set off the knock sensor? So I completely pulled out the rear O2s altogether, so are you reconfirming what others have said about them doing nothing but telling the PCM that the cats are functioning correctly? Everyone else is telling me something different.. Thanks

 

If the y is hitting the floor board then that is your problem. It is setting your knock sensor. I had the same proplem with a pos ory pipe. I just put on the duals and I thought I stole someones car. The knock sensors are very sensitive.

 

thats strange that it feels like you lost low end power. i have to agree with you on the loudmouth bein too loud and raspy but if it bothers you that much, i'd get a diff exhaust. thats what im doin...

the y pipe hitting the floor is really annoying...i need to do somethin about that too

 

polyurethane mounts for the win...

Ben T.

 

You either need to get the rear O2s tuned out or get simms. I bet thats your problem there.

 

My oryp was doing the same thing. I have to agree with everyone above about the o2's. plug in some o2 sims and see if that helps.

 

What do you mean, polyurethane motor or tranny mounts? Or are you talking about one of those clamps with a piece of rubber that keeps the ypipe from banging against the floorboard?

 

I already swapped out the loudmouth resonator for a magnaflow straight through muffler and it's quieter but still full of rasp/drone.. do you think another catback would still help it? Im wondering if the design of the loudmouth catback and not the just muffler selection will have an effect on the sound.. what do you think?