NPP rattling muffler fix
Thread Starter
Racer
Joined: May 2010
Posts: 254
Likes: 1
From: Ellicott City MD
NPP rattling muffler fix
My 08 C6 has the factory NPP exhaust and the passenger muffler started rattling last month and has gotten worse every time I drive it. Seems this is happening to cars with FI and NPP. I have a Novi 1500 at 14 psi, kook’s headers, high flow cats and X pipe making 680 RWHP.
I like the NPP sound at WOT and the wife likes the mild side for cruising. So I decided to attempt to find the rattle and fix it this weekend. I opened up an inspection hole 5 x 5 in the muffler and found the back baffle had 5 cracks in it and the mild side supply pipe welds had cracked. I then cut the entire skin off the muffler. I bought some 16 ga welding plate steel to make baffle support plates for the front and rear internal baffles. I made two templates out of paper then used them to cut out the steel plates to fit each baffle. My brother inlaw did the welding. We welded the cracks and then the support plates. We also welded around all the internal pipes that were only tack welded from the factory. Putting the outer skin back on was difficult. We used a heavy ratchet strap around the muffler and was able to get it tight enough to tack it in place to start the final welds around the entire muffler. I cleaned the welds and used flat black high temp paint to protect the new support plates and welds. Start to finish this took 8 hours. 3 hours cutting it apart and mocking up the plates, 3 hours welding, 1 one hour clean up and paint and 1 hour for removal and replacement. The muffler sounds good and should be strong enough to withstand the exhaust pressure. See the project pics below.
I like the NPP sound at WOT and the wife likes the mild side for cruising. So I decided to attempt to find the rattle and fix it this weekend. I opened up an inspection hole 5 x 5 in the muffler and found the back baffle had 5 cracks in it and the mild side supply pipe welds had cracked. I then cut the entire skin off the muffler. I bought some 16 ga welding plate steel to make baffle support plates for the front and rear internal baffles. I made two templates out of paper then used them to cut out the steel plates to fit each baffle. My brother inlaw did the welding. We welded the cracks and then the support plates. We also welded around all the internal pipes that were only tack welded from the factory. Putting the outer skin back on was difficult. We used a heavy ratchet strap around the muffler and was able to get it tight enough to tack it in place to start the final welds around the entire muffler. I cleaned the welds and used flat black high temp paint to protect the new support plates and welds. Start to finish this took 8 hours. 3 hours cutting it apart and mocking up the plates, 3 hours welding, 1 one hour clean up and paint and 1 hour for removal and replacement. The muffler sounds good and should be strong enough to withstand the exhaust pressure. See the project pics below.
Racer
Joined: Aug 2011
Posts: 289
Likes: 3
From: Alamogordo NM
Nice work, I put Z06 mufflers on my 06 narrowbody and one of them started rattling like crazy. I went to the drag strip one night and apparently the pressure wedged it somehow because its been quiet ever since. 
Thread Starter
Racer
Joined: May 2010
Posts: 254
Likes: 1
From: Ellicott City MD
Thanks it was a lot of work. I figure it is better to reinforce a existing one, rather than replace it with a new one that is likely to just crack again. I hope yours holds.
