Need Muffler advice ----
Melting Slicks
Joined: Mar 2014
Posts: 2,321
Likes: 220
From: Woodbridge, Virginia
NPP is the gm code assigned to the performance exhaust option. It has a valve that is vacuum operated and allows for freer flow and louder sound. This would be toyr next step abive base exhaust system
Instructor
Joined: May 2016
Posts: 150
Likes: 9
From: Frisco Texas
anything with a valve control setup. NPP will probably be the least expensive choice and its really nice to be able to go from stealth quiet to loud with a single click. There is some drone however around highway speeds if flaps are open. I usually only have the flaps open (loud) when I'm on city roads and flaps closed (quiet) on highway. They're usually floating around in the parts for sale section as others are going to more aggressive systems. I have the NPP on my car but I want more roar.
Last edited by ihealy16; Sep 14, 2016 at 05:53 PM.
Pro
Joined: Apr 2014
Posts: 613
Likes: 116
Here is the only sight I know of that still sells them new. If anyone has another site id like to see it. If mine ever goes bad i'll be ordering a new one. You can also buy a remote to open and close the flaps. I leave mine shut most of the time though.
https://www.corvettemods.com/Corvett...FYs9gQod_M4Gug
https://www.corvettemods.com/Corvett...FYs9gQod_M4Gug
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Safety Car
Joined: Dec 2006
Posts: 4,587
Likes: 1,667
From: Pearland / Houston Tx
Advanced
Joined: May 2014
Posts: 69
Likes: 6
Advanced
Joined: Aug 2016
Posts: 87
Likes: 14
From: South Carolina
Update: 11/6/16. After spending almost two months and over 3000 miles with this Flowmaster system, I have to revise my evaluation. There is an annoying DRONE in the 1500 rpm range, which becomes downright obnoxious at anything above the slightest part throttle (like during moderate acceleration). If it wasn't for this, I'd be perfectly happy with this system because at idle, and at any cruising speed that doesn't have the engine turning around 1500 rpm, the sound (both quality and quantify) is just about perfect.
Last edited by Gary7; Nov 6, 2016 at 09:36 AM. Reason: Update
Instructor
Joined: Jan 2015
Posts: 130
Likes: 12
From: So Cal
I just had the Flowmaster Force II axle back installed today. Mean sounding when you're on the throttle, but just a little louder than stock when cruising, and absolutely no drone. Nice rumble at idle and nice pop and burble when you roll off the throttle at higher rpms.
Safety Car
Joined: Sep 2012
Posts: 3,716
Likes: 15
From: Tri Cities TN
I just installed Hooker Blackheart axle back. Its much deeper than the corsa or Borla. It has little or no drone at hwy speed. By the time they are broken in I doubt they will have any drone at all. They sound great. But it may be louder than you want. And they are only $800 at this time.
One thing you will notice about Borla is that the touring are deeper than the S2 which is deeper than the ATAK. IOW, as they get louder they get a higher pitch. I like the Borla sound. I don't like the price.
