[cmitchell17]

The non-NPP I feel is so rare, I have never seen one nor can I find a picture of one. The only picture I can find of the inside of the NPP is the SEMA one.

My problem is I tuned the CCM in HP Tuners to fully close the NPP valves in tour mode. I don't think they ever intended this (yes I know it says in the manual you should never track your car in stealth mode and people seem to take this very literally and think their car will blow up)

However, I don't think they intended it because the sound quality, although it seems very good (low noise, refined sounding, more expensive and luxury sounding) from the outside while the car is revving standing still. From the inside it sounds pretty awful. I have fixed the normal part throttle rattle, but at WOT with the valves closed it still has a rattle type noise.

I am really curious how the regular non-npp exhaust is done, I really don't think its done the same way stealth mode is.

I guess I could try stuffing a rag or something inside the 2 outside pipes with the valve and force the rag into the valve. I have a feeling part of the crappy cheap sound at WOT is due to the valve ratting.

[6spdhyperblue]

Ignore those red pen marks, not mine
I was thinking to cut open the middle and stuff muffler packing in there

That being said I’m shocked you’re saying these things being catted

Would give more of that slp dual/dual sound when closed I bet

[cmitchell17]

Originally Posted by 6spdhyperblue

Ignore those red pen marks, not mine
I was thinking to cut open the middle and stuff muffler packing in there

That being said I’m shocked you’re saying these things being catted

Would give more of that slp dual/dual sound when closed I bet

I want to do the same thing, I just don't have the welding experience to weld it back up. I just bought a cheap wire feeder with some flux core to start with, but welding it back up with that given how much splatter gets everywhere would look horrible, if I can even get it to seal up. I did buy a tig as well but I still have to get gas for it and learn how to do it.

I think (I know at least the C6 does) the corvette NPP has packing in it. I know the Corvette sounds so much better at full WOT than our NPP. That being said our NPP sounds very good but only at about 1/2-3/4 throttle at about 3000-5000 rpms, once you get more on the throttle it starts the raspy/farty/blatty/blappy unrefined noise.

Are you saying removing cats is a good thing for noise?

[arpad_m]

Originally Posted by cmitchell17

The non-NPP I feel is so rare, I have never seen one nor can I find a picture of one. The only picture I can find of the inside of the NPP is the SEMA one.

My problem is I tuned the CCM in HP Tuners to fully close the NPP valves in tour mode. I don't think they ever intended this (yes I know it says in the manual you should never track your car in stealth mode and people seem to take this very literally and think their car will blow up)

However, I don't think they intended it because the sound quality, although it seems very good (low noise, refined sounding, more expensive and luxury sounding) from the outside while the car is revving standing still. From the inside it sounds pretty awful. I have fixed the normal part throttle rattle, but at WOT with the valves closed it still has a rattle type noise.

I am really curious how the regular non-npp exhaust is done, I really don't think its done the same way stealth mode is.

I guess I could try stuffing a rag or something inside the 2 outside pipes with the valve and force the rag into the valve. I have a feeling part of the crappy cheap sound at WOT is due to the valve ratting.

Here is the official, yet very easy to DIY fix for the NPP rattle: https://www.camaro6.com/forums/showt...php?p=10885404. It worked perfectly on my car.

As to why stealth mode is ill-advised at the track, take a gander at this pic (granted, the tips aren't stock and I haven't seen this myself, it's anecdotal, but the assumption of heat buildup with a restriction from permanently closed valves is not unreasonable).

[Sales@Phastek]

I wouldn't recommend blocking the NPP Valves at all and instead just delete them with a new axle back Exhaust. The axle back options that MBRP gives for these 6th Gen SS Camaros are going to give you the performance upgrade over the factory exhaust at the right price.

-Trae

[gtfoxy]

Originally Posted by arpad_m

Here is the official, yet very easy to DIY fix for the NPP rattle: https://www.camaro6.com/forums/showt...php?p=10885404. It worked perfectly on my car.

As to why stealth mode is ill-advised at the track, take a gander at this pic (granted, the tips aren't stock and I haven't seen this myself, it's anecdotal, but the assumption of heat buildup with a restriction from permanently closed valves is not unreasonable).

That’s crazy.

[cmitchell17]

Originally Posted by arpad_m

Here is the official, yet very easy to DIY fix for the NPP rattle: https://www.camaro6.com/forums/showt...php?p=10885404. It worked perfectly on my car.

As to why stealth mode is ill-advised at the track, take a gander at this pic (granted, the tips aren't stock and I haven't seen this myself, it's anecdotal, but the assumption of heat buildup with a restriction from permanently closed valves is not unreasonable).

I did have the NPP rattle and did the fix you linked above and it does work and fixed that rattle. What I am talking about is the rattle type noise at WOT.

Given that it looks like GM never intended for stealth mode to be used besides at low loads, it would seem like the NPP and non-NPP muffler then are very different if the non-NPP is still pretty loud in stealth mode as well especially if GM had to restrict the NPP that much (by looking at the small and small amount of perforations in the pipe in the stealth circuit)

I really don't like how GM just basically "straight piped" the car for the performance exhaust. I thought there were CFR codes that prohibited that loud of exhaust not sure how they got around that haha.

[vtirocz]

Originally Posted by cmitchell17

I did have the NPP rattle and did the fix you linked above and it does work and fixed that rattle. What I am talking about is the rattle type noise at WOT.

Given that it looks like GM never intended for stealth mode to be used besides at low loads, it would seem like the NPP and non-NPP muffler then are very different if the non-NPP is still pretty loud in stealth mode as well especially if GM had to restrict the NPP that much (by looking at the small and small amount of perforations in the pipe in the stealth circuit)

I really don't like how GM just basically "straight piped" the car for the performance exhaust. I thought there were CFR codes that prohibited that loud of exhaust not sure how they got around that haha.

I think the NPP controls strategy (closing the bypass valve even in track mode under certain conditions) is the method for passing the requirements of the CFR in question.

I do like the NPP sound, but overall I think my stock '00 Z28 with the factory SLP "dual/dual" exhaust sounded better with none of the added complexity!

[Jaxcam02]

I can't believe how many people have issues with their NPP systems, I am on my second one and haven't experienced any rattles and it sounds pretty damn good. But that is always subjective, and I was coming from a straight piped beast of a built LS1 fbody.

[gchu]

I'm about 30 minutes north of Philly and have a Non-NPP muffler if anyone wants it to cut apart to post pictures of the inside to compare with NPP

It's free - the only catch is you also need to take the pipes (after the secondary cats) that go back to the muffler as well.... My fiance wants the "junk" gone LOL

[cmitchell17]

Originally Posted by gchu

I'm about 30 minutes north of Philly and have a Non-NPP muffler if anyone wants it to cut apart to post pictures of the inside to compare with NPP

It's free - the only catch is you also need to take the pipes (after the secondary cats) that go back to the muffler as well.... My fiance wants the "junk" gone LOL

I would love to but I am so far from you, I am really curious as to how the non-NPP exhaust sounds. There is so much more to it than just listening to a stupid video of a cell phone camera recording the noise from behind the car while its revving.

[gchu]

Originally Posted by cmitchell17

I would love to but I am so far from you, I am really curious as to how the non-NPP exhaust sounds. There is so much more to it than just listening to a stupid video of a cell phone camera recording the noise from behind the car while its revving.

The stock non-NPP muffler had a light bit of a bark, but definitely none of the rumble/pops like the OEM NPP muffler that replaced it... Nor did it have the cold start "roar" like the OEM NPP muffler - though that could be because it's operating in permanent fused pull mode since it never had the fuse LOL

[Baddawg53]

Originally Posted by cmitchell17

I would love to but I am so far from you, I am really curious as to how the non-NPP exhaust sounds. There is so much more to it than just listening to a stupid video of a cell phone camera recording the noise from behind the car while its revving.

I put the non npp muffler on to get under sound at the track. Car was super loud, cam/heads/LT's/borla atak with the npp.

Not sure exactly where you're at but I'm in northern California, if you wanna hear it hit me up, I'm sure there's a way. It's quiet enough to hear the intake now. Definitely doesn't sound impressive, you can still hear the cam chop but it's lost most of it's bark now.

[cmitchell17]

Originally Posted by Baddawg53

I put the non npp muffler on to get under sound at the track. Car was super loud, cam/heads/LT's/borla atak with the npp.

Not sure exactly where you're at but I'm in northern California, if you wanna hear it hit me up, I'm sure there's a way. It's quiet enough to hear the intake now. Definitely doesn't sound impressive, you can still hear the cam chop but it's lost most of it's bark now.

I am across the country in SC but thanks for the offer. I guess first thing I need to do is find someone else to drive my car so I can actually hear it from third person.