Low Cost NPP modification for more volume

SkiRideDrive · 08-30-2018, 06:20 PM

Hey there.

I was pondering the least expensive way to get a bit more volume out of the NPP muffler when in full open mode. Some aftermarket companies have solutions in the 1200 dollar range and some folks have replaced the suitcase with aftermarket mufflers, etc.

I'm not sure if there is enough clearance under the car, but was thinking that maybe adding pipe to bypass the muffler for each valve could give a bit more volume for minimal investment. This would also allow the car to remain quiet in stealth mode. I have a super quality MS Paint drawing below with black lines showing where the theoretical bypass pipes would go.

Any thoughts?

Indyblue98 · 08-30-2018, 06:37 PM

Air will follow path of least resistance.
Doubt much of it will be flowing thru the 90 degree added pipe ,
and even the little that does will not affect the volume coming out of the same exhaust port.

TJay74 · 08-30-2018, 06:42 PM

I am willing to bet it wont give you less than a 10% increase in sound volume. When that valve is open, minimal exhaust flow goes thru the internal muffler.

SkiRideDrive · 08-30-2018, 06:49 PM

I hear both of you, but I think that maybe flow and sound aren't always directly related. If a muffler deleted camaro is significantly louder than an NPP camaro in full open mode, I have a feeling that bypassing the muffler may produce additional volume. There is also the option of adding a Y in the system instead of a T.

Bobkd · 08-30-2018, 08:02 PM

If you could block the exhaust coming out of the muffler case next to the npp valve that would get you what you're looking for. With the valve closed it could still go into the muffler and out the inside outlets for stealth mode.

KingLT1 · 08-30-2018, 10:14 PM

Install CA cat deletes and the NPP will get much louder when open.

VinnAY · 09-01-2018, 06:19 AM

Quote:

Originally Posted by KingLT1

Install CA cat deletes and the NPP will get much louder when open.

Too many people have said it get's raspy this route when I was thinking of the 2d cat delete option

SC88 · 09-01-2018, 07:13 AM

Headers and no cats will make it 10x louder. I also wouldn’t judge the sound from inside. The sound deading used on these cars is incredible I didn’t realize how loud my car was until I heard it going down the road.

parish8 · 09-01-2018, 07:45 AM

I removed all 4 cats and it was very loud open and still quiet closed. I wouldn't expect much of a change in sound with a bypass.

cmitchell17 · 09-01-2018, 09:07 AM

Is it just me or does anyone else think the NPP is too raspy sounding in stock form? It sounds really good at low-mid throttle but once it goes WOT at high rpms it starts sounding obnoxious and raspy?

I have tried to play with HP tuners tables and command the valves closed at WOT, but its still just as loud.

With the valves closed it does look very restrictive having to flow through those small holes. I have measured with 5hp difference (as advertised with the corvette NPP) with virtual dyno comparing stealth mode to track with virtual dyno.

zoutlawss · 09-01-2018, 10:47 AM

Damn delete that big ugly thing and enjoy the Roar. I did the muffler delete and secondary cat delete and car sounds awesome. You can hear the results at the beginning and end of video. Also gives you before and after

TJay74 · 09-01-2018, 07:50 PM

When I had my 1LE I did the secondary cat deletes 1st, it sounded great and the car picked up some power. Then I put the ARH catless headers with the full system on it where it connects right before the NPP muffler, loud is an understatement for sure.

Personally I like the raspier sounding exhaust in the form of an exotic tone. I dont like the deep rumble like an old chevy pick up with Flowmasters on it sound. That is just my preference, others opinions may vary.

SomeGeoffGuy · 09-05-2018, 11:35 AM

sounds like you are describing the Hooker Blackheart exhaust. Not a low price option though!

-Geoff

KingLT1 · 09-05-2018, 01:19 PM

Quote:

Originally Posted by VinnAY

Too many people have said it get's raspy this route when I was thinking of the 2d cat delete option

Not if you keep the secondary cats.

08-30-2018, 06:20 PM	#1
SkiRideDrive Drives: WTB Camaro Join Date: Aug 2018 Location: San Diego Posts: 11	Low Cost NPP modification for more volume Hey there. I was pondering the least expensive way to get a bit more volume out of the NPP muffler when in full open mode. Some aftermarket companies have solutions in the 1200 dollar range and some folks have replaced the suitcase with aftermarket mufflers, etc. I'm not sure if there is enough clearance under the car, but was thinking that maybe adding pipe to bypass the muffler for each valve could give a bit more volume for minimal investment. This would also allow the car to remain quiet in stealth mode. I have a super quality MS Paint drawing below with black lines showing where the theoretical bypass pipes would go. Any thoughts?

08-30-2018, 06:42 PM	#3
TJay74 Drives: 17 Camaro SS 1LE & 16 Sierra AT CC Join Date: Nov 2016 Location: Norman, OK Posts: 2,424	I am willing to bet it wont give you less than a 10% increase in sound volume. When that valve is open, minimal exhaust flow goes thru the internal muffler. __________________ 2019 Corvette Z06 2LZ A8 - Halltech CAI, AWE non-catted X-pipe, Mamo V2 ported TB 592rwhp, bone stock 566rwhp 2017 Camaro SS 1LE - Procharger D1SC w/ Tial 2" BOV & Race intercooler / ARH full length catless headers / Alky meth injection system - 650rwhp on conservative tune SOLD

08-30-2018, 10:14 PM	#6
KingLT1 Drives: 2016 1SS NFG A8 Join Date: Aug 2017 Location: 46804 Posts: 7,665	Install CA cat deletes and the NPP will get much louder when open. __________________ 2016 NFG SS A8/Whipple 2.9/Fuel System/Flex Fuel

09-01-2018, 07:13 AM	#8
SC88 Twin Turbo Drives: 2016 2SS Join Date: Jul 2016 Location: Illinois Posts: 290	Headers and no cats will make it 10x louder. I also wouldn’t judge the sound from inside. The sound deading used on these cars is incredible I didn’t realize how loud my car was until I heard it going down the road. __________________ Boost, Boost & More Boost Instagram = BoostedSS

09-01-2018, 07:45 AM	#9
parish8 Drives: 17 SS a8 Join Date: Feb 2010 Location: omaha Posts: 1,678	I removed all 4 cats and it was very loud open and still quiet closed. I wouldn't expect much of a change in sound with a bypass. __________________ dropped a valve in the 6.2. now running a drop in rods and piston 5.3 best et 5.83@121 with the 5.3 http://www.camaro6.com/forums/showthread.php?t=465472

08-30-2018, 06:37 PM	#2
Indyblue98 2012 RS 2ss Drives: 2018 ZL1 2012 2SS WhippleCharged Join Date: Feb 2012 Location: Kansas Posts: 414	Air will follow path of least resistance. Doubt much of it will be flowing thru the 90 degree added pipe , and even the little that does will not affect the volume coming out of the same exhaust port.

08-30-2018, 06:49 PM	#4
SkiRideDrive Drives: WTB Camaro Join Date: Aug 2018 Location: San Diego Posts: 11	I hear both of you, but I think that maybe flow and sound aren't always directly related. If a muffler deleted camaro is significantly louder than an NPP camaro in full open mode, I have a feeling that bypassing the muffler may produce additional volume. There is also the option of adding a Y in the system instead of a T.

08-30-2018, 08:02 PM	#5
Bobkd Drives: 2018 1ss, 2021 silverado HD Join Date: Jul 2017 Location: wny Posts: 68	If you could block the exhaust coming out of the muffler case next to the npp valve that would get you what you're looking for. With the valve closed it could still go into the muffler and out the inside outlets for stealth mode.

09-01-2018, 09:07 AM	#10
cmitchell17 Drives: 17 2SS, 8L90, Cam, Heads, E85 Join Date: Dec 2016 Location: US Posts: 1,213	Is it just me or does anyone else think the NPP is too raspy sounding in stock form? It sounds really good at low-mid throttle but once it goes WOT at high rpms it starts sounding obnoxious and raspy? I have tried to play with HP tuners tables and command the valves closed at WOT, but its still just as loud. With the valves closed it does look very restrictive having to flow through those small holes. I have measured with 5hp difference (as advertised with the corvette NPP) with virtual dyno comparing stealth mode to track with virtual dyno.

09-01-2018, 07:50 PM	#12
TJay74 Drives: 17 Camaro SS 1LE & 16 Sierra AT CC Join Date: Nov 2016 Location: Norman, OK Posts: 2,424	When I had my 1LE I did the secondary cat deletes 1st, it sounded great and the car picked up some power. Then I put the ARH catless headers with the full system on it where it connects right before the NPP muffler, loud is an understatement for sure. Personally I like the raspier sounding exhaust in the form of an exotic tone. I dont like the deep rumble like an old chevy pick up with Flowmasters on it sound. That is just my preference, others opinions may vary. __________________ 2019 Corvette Z06 2LZ A8 - Halltech CAI, AWE non-catted X-pipe, Mamo V2 ported TB 592rwhp, bone stock 566rwhp 2017 Camaro SS 1LE - Procharger D1SC w/ Tial 2" BOV & Race intercooler / ARH full length catless headers / Alky meth injection system - 650rwhp on conservative tune SOLD

09-05-2018, 11:35 AM	#13
SomeGeoffGuy Drives: 2023 2SS Convertible Join Date: May 2009 Location: Metro Detroit Posts: 1,202	sounds like you are describing the Hooker Blackheart exhaust. Not a low price option though! -Geoff __________________ '12 2SS RS Convertible - Traded in. '16 2SS Convertible - White on white, mag-ride, NPP, nav. Sold! '23 2SS Convertible -Same as above except orange.

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