Got the 427 GMMG ZL1 back today and just as we thought the GMMG chambered exhaust sounds like open headers.....only louder!! Under any accelleration at all the sound could probably be heard for half a mile. We are going to up the boost to 10 psi when I take it back in a month so during that time I need to find out how some of you have fixed this problem. BTW - with 4 psi and initial tuning it put down 657 rwhp through a Moser 4.10. With 10 psi and 800+ rwhp it is only going to be worse.

 

Cats?

 

It's got cats.

 

i hate to say it, but you could get a new catback, then a bullet in the i pipe

 

May have to do just that. I'd like to keep the OE exhaust if I can though.

 

SLP D/D. It's quieter than my old magnaflow. Either that or a factory exhaust, but that would probably cost you a little flow.

 

my car is quieter...i'll trade ya????

 

how much you want for it?

 

I can make it quieter. Just give me your 427. I really don't know how you expect a 650+rwhp machine to be quiet.

 

It is not streetable as is. I was wrong. There are no cats. This thing sounds like a NASCAR hot rod on steroids coming down the road!! Got to try a Borla cat back or something.

 

well get cats! that will help alot

 

I don't know that a Borla is going to help with quieting it down, unless you run a closed plate on it, look into Hooker, Magnaflow,SLP Dual/Dual, or the SLP 2OTL, all are quiet exhaust with pretty nice flow. I would throw cats on there first to see if it quiets down. I bet that 427 sounds like a beast through the GMMG!

 

Add a Borla XR1 to the I-Pipe?

 

I don't know where the cats would fit? I do think I'll swap the SLP exhaust from my SS to the ZL1. If it will fit. Yeah, it's loud. Scares small children, aminals just run and women think the end of the world is coming.

 

This is what I did...of course, I'm not sporting 427 cubic inches...

 

 

I will probably try adding something after the y-pipe and go from there. I don't like driving around in a 100 degree car feeling like I've just robbed a bank hoping a cop doesn't hear or see me. It's not a relaxing way to drive.

 

if you have an ORY-pipe get CATS, and if thats not enough get a Bullit muffler (Dynomax, Borla XR-1, or even some other chambered mufflers ike Stainless Works, Sweet Thunder, etc.)

If you don't lik ehtat you don't deserve a car from GMMG! lol j/k...If you have the GMMG badge on your car, I'll take it if you don't like/want it (i highly doubt that will happen )

 

You're gonna need cats and a different catback.

Look into SLP D/D, SLP 2OTL, Hooker, or Magnaflow.