Just Installed Flowmaster 40s
 

So I pulled the trigger on a pair of Flowmaster 40s for my npp system. Startup is amazing and it shakes the ground, as a muscle car should. Drone is a bit annoying at lower rpms at low speed but almost zero on the highway. My only complaint is that at higher rpms the exhaust is quite a bit quieter than the npp:bonk:. Anyone know of a different muffler that I could swap in that would give me that scream that the npp has at the top end?

How it sound?:noidea:

It sounds pretty good, super deep on startup but once you really get on it, it looses that iconic scream that the stock npp has. I’m thinking about switching to maganflows, but I’m not sure if they are going to be louder than the stock npp

That is because on NPP when you go WOT the valves open and bypass the sound damping in the muffler. No true muffler will be louder then bypassing the muffler.

The entire point of NPP is to be able to go from mild to loud. Your setup is now medium to medium. A louder muffler will likely introduce more noise at all rpm range.

MBRP might be what you are after at this point. Loud with no drone...

You might prefer the Flowmaster American Thunder NPP exhaust. Basically it's a super 40 in "quiet" form and then when the valves open it goes through to the outlaw muffler which is practically straight pipe. This will also retain the muscle car rumble as well.

Please post a video from outside car.

That is what I have...it's pretty good. Makes the factory NPP sound like a kitten compared to a lion above 3k rpm, but still civil with valves closed. Does have a little drone right around 1500rpm but I don't have cats.

I have the flowmaster 817746 (American thunder 409S Stainless Steel) with dual mode exhaust npp. If you want the loudest set-up with NPP, pull fuse 51. Then, the valves never close, and the exhaust will stay in Outlaw the whole time. I think that may be the sound you are looking for. Let me know if you need help with the fuse.

if you pull the fuse then its no longer NPP. might as well just buy a non npp exhaust and save money.

Gotta agree with that one.

Depends on the coin you wanna spend. I bought the Borla Atak with secondary cat delete and NPP compatibility. Louder than the NPP stock setup in all RPM ranges and I can still put it in stealth mode if I don't feel like waking my neighbors..much..

Stealth mode is great with the ATAK. Sadly I wish that I didn't have to comb through all the menus for it, since Tour will still open the valves.

True, but one of the reasons I pulled the fuse was because I could hear the valves open and close. In addition, the NPP valves would rattle and vibrate when closed.

Engine Masters ( Motortrend series ) recently did a test on noise vs flow ( hp) including baffled type mufflers like 40 series.

hey all, thanks for all of the great responses, Ill be posing a vid of the exhaust soon for everyone out there who is considering doing this exhaust. If you don't have the NPP I would definitely recommend it, If you do have the NPP you will be disappointed from what I have found. I ended up buying a used Flowmaster American thunder NPP system a couple of days ago, and I'll be switching them out soon.