Disappointed after adding NPP - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

Camaro__ss · 09-02-2020, 10:04 PM

I’ve had NPP mufflers (I think from a ZL1) and catless headers for awhile and I’m happy with the sound. But I always wanted to hook up a vacuum controller to the mufflers and I finally took the time to do it. Waste of time.
I used a MAC 3 way solenoid and a 1 channel wireless controller, vacuum from the back of the intake. It works as intended, but there really is no substantial difference in sound in the 2 modes inside the car. Behind the car a there’s little difference but who cares about that? I did this on my corvette and there was a big difference. Anyway, thought I would share in case someone else was thinking of going through the drill.

WHAMMO · 09-02-2020, 10:14 PM

It reduces drone on the highway, and better for your neighbors in the morning...but its just that.

Silveradoss573 · 09-02-2020, 10:27 PM

Mines day and night between the 2 modes.

O.F. · 09-03-2020, 05:47 AM

I like mine too.

RobZL1 · 09-03-2020, 09:22 AM

Quote:

Originally Posted by Silveradoss573

Mines day and night between the 2 modes.

Ditto.

Camaro__ss · 09-03-2020, 04:22 PM

Strange I can’t tell much difference inside the car. Outside the car I can hear a difference if I stand directly behind it. I still have the factory middle muffler/crossover/resonator thing that is between the headers and the NPP mufflers, maybe that’s why I can’t tell. Maybe I’m going deaf.

InFiD3ViL · 09-03-2020, 11:44 PM

The factory L99 suitcase resonator? That may be the issue. Maybe an H pipe and some new pipes or an X pipe is in order? That L99 resonator acts as an H pipe or crossover pipe, but it also acts as a resonator/muffler to quiet the AFM activation down some. The LS3 doesn't have it and has a true H pipe in that location.

I don't know how much of a difference it made when I deleted mine as I also did a muffler delete and x pipe at the same time. But I'm sure it has to have some effect on volume. Hopefully someone else will chime in on it. Catless headers + open NPP should sound much louder than closed.

Ashen L99 · 09-04-2020, 05:31 AM

My friend/neighbors zl1 has longtubes hooked up to the factory NPP and the flaps make a very noticeable difference. He pulled the fuse though, he likes to party.

Modernmusclecar · 09-04-2020, 10:01 AM

That l99 resonater will definitely make a difference. Remove and put and x pipe in its place. ...and leave the flaps open haha. Also a good exhaust puts the noise out the back instead of in the car. ..that's what you want.

Black 6.2L SS · 09-11-2020, 09:10 PM

Big difference when my flaps are closed versus open.

RupertPupkin · 09-12-2020, 10:02 AM

Op do a muffler mod, if you want to hear a difference. That’s what I did on mine. Stock NPP mufflers are very subtle when open/closed when idling and/or going WOT. Even for my C6Z, it wasn’t a huge difference.

FasNuf · 09-12-2020, 11:42 AM

The difference while cruising isn’t that much except for drone. Idling is quite a bit louder, and wide-open throttle is a huge difference. On mine anyway I don’t really like the sound wide-open throttle with no muffler.

Vegas Bound · 09-12-2020, 05:16 PM

Quote:

Originally Posted by Silveradoss573

Mines day and night between the 2 modes.

#metoo.

Mike Cordero · 10-17-2020, 07:13 AM

I have a 2012 SS Camaro. Recently bought some npp mufflers fron ZL1 car just to get the dual mufflers tips look and getting some extra sound. I have the factory exhaust manifolds and cats which im planning to maintain for now. I seen a kind of beeper to open and close the npp valves. How that work and what else i will need to operate them? Thanks for your advice.

09-02-2020, 10:04 PM	#1
Camaro__ss Drives: 2013 L99 Join Date: Jan 2019 Location: San Antonio TX Posts: 185	Disappointed after adding NPP I’ve had NPP mufflers (I think from a ZL1) and catless headers for awhile and I’m happy with the sound. But I always wanted to hook up a vacuum controller to the mufflers and I finally took the time to do it. Waste of time. I used a MAC 3 way solenoid and a 1 channel wireless controller, vacuum from the back of the intake. It works as intended, but there really is no substantial difference in sound in the 2 modes inside the car. Behind the car a there’s little difference but who cares about that? I did this on my corvette and there was a big difference. Anyway, thought I would share in case someone else was thinking of going through the drill.

09-02-2020, 10:14 PM	#2
WHAMMO Drives: 13' 1LE Join Date: Apr 2012 Location: Canada Posts: 2,641	It reduces drone on the highway, and better for your neighbors in the morning...but its just that. __________________ 13' 1LE Old setup: TSP 231-236/Tick 660/.105 PR, UDP, SW LT 2'' & HFC, stock NPP & H pipe, VR-DRX CAI, air scoop, Goertz1 manifold, 102mm BBK, 26" Toyo DRs, Forgestars R17x10 & F18x8, rear seat delete, remote Pat G tune Autocal, 7400 limiter, Spec Mini Twin. 91oct. 11.90@122.3, 0-60ft 2.0 / 11.99@123.6, 0-60ft 2.1 DA+819 ...519RWHP SAE Solid roller SBE LS3, FED, LLSR, 91oct, 605rwhp N/A. Tuned by Pat G. Build by me.

09-03-2020, 11:44 PM	#7
InFiD3ViL Drives: 2010 CGM 2SS/RS LS3 Swapped A6 Join Date: Sep 2016 Location: Spring Hill, FL Posts: 4,570	The factory L99 suitcase resonator? That may be the issue. Maybe an H pipe and some new pipes or an X pipe is in order? That L99 resonator acts as an H pipe or crossover pipe, but it also acts as a resonator/muffler to quiet the AFM activation down some. The LS3 doesn't have it and has a true H pipe in that location. I don't know how much of a difference it made when I deleted mine as I also did a muffler delete and x pipe at the same time. But I'm sure it has to have some effect on volume. Hopefully someone else will chime in on it. Catless headers + open NPP should sound much louder than closed. __________________ 2010 CGM Camaro 2SS LS3 Swapped A6 - GPI LS3 SS1 .647/.638, (224/237, 112 +4, 7º overlap) on CamMotion 8620 core, BTR Platinum .660" Dual Spring kit w/titanium retainers, CHE bronze trunnion upgrade, stock heads milled @ .015, Melling HV 10296 oil pump, TSP 1-7/8" long tube headers (W/Catless Off-road Pipes), Corsa Xtreme 3" Catback, GPI Ported/Rod Mod Intake, Stage 2 Ported Throttle Body, Vararam OTR CAI, Mike Norris Gen 2 catch can + GM 1LE clean side separator, 160º thermostat - Megan Racing adjustable coilovers (lowered 1.75"), MRR M017 10/11" wheels-Tuned by Ryan @ GPI

09-04-2020, 05:31 AM	#8
Ashen L99 Drives: Ashen grey, 1SS, L99 Join Date: Aug 2016 Location: Oklahoma Posts: 527	My friend/neighbors zl1 has longtubes hooked up to the factory NPP and the flaps make a very noticeable difference. He pulled the fuse though, he likes to party. __________________ Roto-fab CAI, Nick Williams 102mm TB, LOD X1 V3 intake manifold, GMPP LS3 heads, Night Fury cam, TSP 2” long tubes, Corsa ZL-1 catback, Nitrous Outlet 102mm plate kit/150 shot, NGK BR7EF plugs with Taylor plug wires, DSX flex fuel kit, ZL-1 fuel pump and injectors, B&M deep trans pan, Yank 3400 converter, 3.45s with BMR Delrin bushings, mishimoto 169° Thermostat, GM ground effects, T-Rex upper grill, Z/28 Spoiler, Lolly pop Lime brake calipers, ZL1 10 spoke wheels, 12” subwoofer, and custom paint matched interior.

09-12-2020, 10:02 AM	#11
RupertPupkin Drives: 2014 Camaro SS 1Le Join Date: Feb 2016 Location: IL Posts: 1,583	Op do a muffler mod, if you want to hear a difference. That’s what I did on mine. Stock NPP mufflers are very subtle when open/closed when idling and/or going WOT. Even for my C6Z, it wasn’t a huge difference. __________________ 2014 SS 1LE Money Pit/ Forged 402 CAM 22X/24X, .619/.617, 113 LSA/ LS9 Heads FIC 1200cc/DSX Aux Pump//McLeod RXT Clutch 730whp: 630Trq

09-02-2020, 10:27 PM	#3
Silveradoss573 Drives: Camaro 1LE Join Date: May 2018 Location: USA Posts: 1,348	Mines day and night between the 2 modes.

09-03-2020, 05:47 AM	#4
O.F. Drives: 2015 BLK/BLK 2SS/RS MN6 Join Date: Oct 2016 Location: New Hampshuh Posts: 266	I like mine too.

09-03-2020, 04:22 PM	#6
Camaro__ss Drives: 2013 L99 Join Date: Jan 2019 Location: San Antonio TX Posts: 185	Strange I can’t tell much difference inside the car. Outside the car I can hear a difference if I stand directly behind it. I still have the factory middle muffler/crossover/resonator thing that is between the headers and the NPP mufflers, maybe that’s why I can’t tell. Maybe I’m going deaf.

09-04-2020, 10:01 AM	#9
Modernmusclecar Drives: 2011 Camaro SS Join Date: Jul 2019 Location: Parts unknown Posts: 820	That l99 resonater will definitely make a difference. Remove and put and x pipe in its place. ...and leave the flaps open haha. Also a good exhaust puts the noise out the back instead of in the car. ..that's what you want.

09-11-2020, 09:10 PM	#10
Black 6.2L SS Drives: 2014 1SS/RS, LS3, NPP Join Date: Feb 2019 Location: Florida Posts: 184	Big difference when my flaps are closed versus open.

09-12-2020, 11:42 AM	#12
FasNuf Drives: 2014 Camaro ZL1 Join Date: Jul 2019 Location: Oregon Posts: 1,609 View My Garage	The difference while cruising isn’t that much except for drone. Idling is quite a bit louder, and wide-open throttle is a huge difference. On mine anyway I don’t really like the sound wide-open throttle with no muffler. __________________ . . . . https://www.youtube.com/channel/UCgN...etl17hA/videos

10-17-2020, 07:13 AM	#14
Mike Cordero Drives: 1971 Camaro Z-28 Join Date: Sep 2015 Location: Puerto Rico Posts: 319	NPP MUFFLERS first grade class needed I have a 2012 SS Camaro. Recently bought some npp mufflers fron ZL1 car just to get the dual mufflers tips look and getting some extra sound. I have the factory exhaust manifolds and cats which im planning to maintain for now. I seen a kind of beeper to open and close the npp valves. How that work and what else i will need to operate them? Thanks for your advice.