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Noisy exhaust...still!

P

paulhunde

New member
Hi guys,

I posted earlier about how I put an SLP exhaust on my GXP, and it was pretty loud. So, I just had a resonator installed, and it is still way too loud for my liking. I really don't want to change the whole exhaust, so I was thinking about replacing the SLP mufflers with something else, or even changing the cat converter to something better. Any thoughts?
 


I have borla pro xs which are supposed to be some of the quietest; I've also got a 18" resonator.
That being said, my whole interior shakes at 2.25k rpm, the car is still very loud.

I'm thinking the tiny 3" flowmaster cat I have is a big reason for a lot of the noise, more-so than the mufflers...
 


SLP's droned like crazy when I had them.

I had a catless downpipe, a bullet style muffler in the middle for a resonator, and two Borla Pro XS' out back.

No more drone. Much better setup.
 
paulhunde said:
I went with a Vibrant Ultra Quiet. You're saying I should add 1? Where would it go?
Click to expand...
I researched a bunch of long 2.25" resonators. There's like 30" of room where the stock resonator goes. Thread, (sry it won't be the right diameter) - http://www.grandprixforums.net/threads/105705-Resonators-Now-with-some-part-numbers

Someone, besides me, wondered if something could even fit here safely on 04+. I dunno if they ever got a response.

2017-05-07%2013.44.06.jpg
 
blueguy91 said:
SLP's droned like crazy when I had them.



I had a catless downpipe, a bullet style muffler in the middle for a resonator, and two Borla Pro XS' out back.

No more drone. Much better setup.
Click to expand...

So, if I replace the SLPs with Borlas, would it be enough you think? I still have stock cat though
 
blueguy91 said:
SLP's droned like crazy when I had them.

I had a catless downpipe, a bullet style muffler in the middle for a resonator, and two Borla Pro XS' out back.

No more drone. Much better setup.
Click to expand...

blueguy91 said:
Most likely; because SLP's suck.

Before: https://www.youtube.com/watch?v=1AHTsY4TpYo

After: https://www.youtube.com/watch?v=pbE25ajERSU

However; the real restriction is the downpipe. Go get a 3" one. That'll help more than anything.
Click to expand...

Sweet, thanks for the before and after. Big difference. What brand down pipe did you go with?
 


ZZP's catless.

I don't think there is another option for the LS4. I'm sure if you had the mechanical know how, a set of headers would be better obviously (the EBay ones are actually fine) and then just take it somewhere and have a cat welded in it.
 
Brandon Furches actually bought materials to make about 20 downpipes, like 3 people bought them, and those 3 aren't quite done, maybe they are, I don't know for sure, but he is probably a better option for a downpipe if you are willing to be patient.
 
The ZZP one is just fine; especially for the money. I had to have it made solid because of the X11 mounts in my car. All I did was removed the flex.
 
Looks like I'm gonna go that route. One question though, I'm probably gonna be selling her in a year or so and getting another one with less miles. Aren't I gonna have an issue with a catless pipe?
 
If your state has a visual inspection like Connecticut does, yes you will automatically fail emissions and will not be tested until the catalytic converter is replaced.
 


I'm going to be selling my OEM cat soon if you're interested. 98k miles and it's in good shape. I took it out cause I transferred my catless DP from my 97 GP and put in the 06.
 
SaukRapids said:
Definitely going to have trouble with the sale and no cat. So, you'd likely have to buy one then anyway. :p
Click to expand...

Most car people have "inspections" so they don't have to worry about all that "OMGNOITSCATLESS" business.

Or just move to the Midwest where no one cares about anything like that.
 
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