NPP 2.5" to 3" - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

LETHAL2SS · 09-17-2018, 02:43 PM

I recently picked up a practically new NPP catback off a ZL1,

I have 3" exhaust all the way back right now and I'm trying to figure out if anyone else has modified it or cut it and linked it to a 3" system they already had and had any pointed, I'm decent with a welder enough to "get the job done" but they're never pretty, so I'd like to avoid that.

I have clamps at the axle on my 3" and it steps down to 2.5" for the mufflers. I had an idea to cut the NPP right where the mid-pipe splits for the Mufflers but figured I'd ask the land of knowledge here first!

I'll try and get some pictures of what I'm explaining here as as soon as I make it over to the shop.

zz430camaro · 09-17-2018, 03:03 PM

Few questions

1. Why are you getting rid of your system now?
2. If the NPP is an entire factory welded system, why would you not just put the entire thing in? No sense leaving portions of the 3" system in there.

LETHAL2SS · 09-17-2018, 04:49 PM

The system I have now has the GMPP touring mufflers and is much too quiet for me, the NPP mufflers have a much better tone IMO.
the NPP comes with a H-pipe set up, it's 2.5 inches and my current system is 3 in.
I don't want to lose my current X-pipe 3 in. flow and go to a lesser system yet I want the mufflers

HOJO · 09-17-2018, 05:04 PM

Does that defeat the purpose of the 3 inch if you neck it back down to 3 inch?

zz430camaro · 09-17-2018, 05:33 PM

You can cut anything off you want and adapt the mufflers to your current 3" system. By necking the system back down to 2.5" you pretty much loose all the benefits of the larger pipes, that 3" center section with the x pipe wont do shit. I just think cutting off the 3" stuff to weld on 2.5" NPP mufflers is kind of pointless, just install the entire NPP exhaust and sell your old set up. It will fit up really nice and save you the aggrivation of splicing two different size exhaust systems together.

LETHAL2SS · 09-17-2018, 05:42 PM

Quote:

Originally Posted by zz430camaro

You can cut anything off you want and adapt the mufflers to your current 3" system. By necking the system back down to 2.5" you pretty much loose all the benefits of the larger pipes, that 3" center section with the x pipe wont do shit. The NPP is a good system and will support 500 HP naturally aspirated no problem. I have the factory NPP on my cammed car and put down 485 no problem. I just think cutting off the 3" stuff to weld on NPP mufflers is kind of pointless, just install the entire NPP exhaust and sell your old set up. It will fit up really nice and save you the aggrivation of splicing two different exhaust systems together. Thats just my opinion.

I'm Supercharged cammed with aftermakret heads, little bit more than just 500whp.

the cut down to 2.5" right at the muffler hasnt held me back yet.

olblue75 · 09-17-2018, 07:50 PM

I can tell you the NPP mufflers they use on a Z28 with a 2 3/4 is the same as a ZL1/1LE with a 2 1/2 they just neck down at the mufflers I have a set in the garage.

camguynj · 09-17-2018, 08:31 PM

Billy Boat makes a complete 3" cat back NPP system for Vettes. May want to contact them and ask about just their 3" mufflers.

Another option to increase the stock 2.5" NPP muffler sound would be to remove the muffler's inner perforated pipe and replace it with a solid one to get a straight thru flow ...see this thread https://www.camaro5.com/forums/showthread.php?t=480088

christianchevell · 09-18-2018, 05:37 PM

You do know the problems with installing and making function the NPP system on a non NPP car and their vacuum activators ? And have a new rear valance? there have been posts on here before. you could just lash them open.....or closed....

derieu · 09-18-2018, 05:46 PM

you wont be losing anything if the only 2.5" part of the exhaust is at the mufflers. If you were super picky about it, cut the muffler open and just replace all of the 2.5" joints with 3" pipe. People use to mod the old z06 bimode exhaust mufflers. Just takes some labor

olblue75 · 09-18-2018, 07:49 PM

They are default in the open position. Also remove the resonator and install a X Pipe.

zz430camaro · 09-18-2018, 09:01 PM

The NPP mufflers are good because they dont drone at all really, its a mellow exhaust until you punch it then it sounds good. I just leave em opened up all time, not need to ^uck around with those valves.

christianchevell · 09-19-2018, 09:17 AM

Yup I drive with mine open..... and tuned excellent with decel popping not removed. But loved...……..

09-17-2018, 02:43 PM	#1
LETHAL2SS Drives: 2011 Camaro 2SS Join Date: May 2016 Location: Houston, TX Posts: 413	NPP 2.5" to 3" I recently picked up a practically new NPP catback off a ZL1, I have 3" exhaust all the way back right now and I'm trying to figure out if anyone else has modified it or cut it and linked it to a 3" system they already had and had any pointed, I'm decent with a welder enough to "get the job done" but they're never pretty, so I'd like to avoid that. I have clamps at the axle on my 3" and it steps down to 2.5" for the mufflers. I had an idea to cut the NPP right where the mid-pipe splits for the Mufflers but figured I'd ask the land of knowledge here first! I'll try and get some pictures of what I'm explaining here as as soon as I make it over to the shop. __________________ 2010 Camaro 2SS-Mods: Nightfury cam, CNC ported LS3 heads, CNC ported TB, Ported Intake, RX Catch Can, MGW Short Throw Shifter, Mantic 9000 Clutch, TSP 1 7/8 headers, catless NPP, BMR trailing arms, MMR Z/28 Reps 20" gloss black. SOLD 2011 Red Jewel Tintcoat 2SS-Mods: Edlebrock E Force S/C w/ 3" pulley swap,Texas Speed roller Boost Cam 227/235, 641"/649", 114 LSA, PRC Ported Heads, Ported TB,ARH 1 7/8 headers, McLeod RST twin disk 1000 hp clutch, ZL1 Fuel Pump, 620whp

09-17-2018, 04:49 PM	#3
LETHAL2SS Drives: 2011 Camaro 2SS Join Date: May 2016 Location: Houston, TX Posts: 413	The system I have now has the GMPP touring mufflers and is much too quiet for me, the NPP mufflers have a much better tone IMO. the NPP comes with a H-pipe set up, it's 2.5 inches and my current system is 3 in. I don't want to lose my current X-pipe 3 in. flow and go to a lesser system yet I want the mufflers __________________ 2010 Camaro 2SS-Mods: Nightfury cam, CNC ported LS3 heads, CNC ported TB, Ported Intake, RX Catch Can, MGW Short Throw Shifter, Mantic 9000 Clutch, TSP 1 7/8 headers, catless NPP, BMR trailing arms, MMR Z/28 Reps 20" gloss black. SOLD 2011 Red Jewel Tintcoat 2SS-Mods: Edlebrock E Force S/C w/ 3" pulley swap,Texas Speed roller Boost Cam 227/235, 641"/649", 114 LSA, PRC Ported Heads, Ported TB,ARH 1 7/8 headers, McLeod RST twin disk 1000 hp clutch, ZL1 Fuel Pump, 620whp

09-17-2018, 07:50 PM	#7
olblue75 Drives: 2010 2SS/RS Join Date: Dec 2009 Location: Clarksville Tennesse. Posts: 6,064	I can tell you the NPP mufflers they use on a Z28 with a 2 3/4 is the same as a ZL1/1LE with a 2 1/2 they just neck down at the mufflers I have a set in the garage. __________________ Orange Krush II 1LE Front sway bar, Splitter, shocks and struts, Z28 dual mode mufflers, Intake, UCA Bushings, and Toresen 3.91 Diff. 1 piece DSS Drive Shaft, ZL1/C7 Calipers, and 32mm JPSS Rear Bar. ASC race spec splitter and wicker. 6th Gen M017 Wheels. Stainless Works 1 7/8 LTs. DSE and PAFDT Suspension components.

09-17-2018, 08:31 PM	#8
camguynj Drives: '13 SS/RS LS3 BRM Cammed NPP Join Date: Jan 2013 Location: NJ Posts: 3,812 View My Garage	Billy Boat makes a complete 3" cat back NPP system for Vettes. May want to contact them and ask about just their 3" mufflers. Another option to increase the stock 2.5" NPP muffler sound would be to remove the muffler's inner perforated pipe and replace it with a solid one to get a straight thru flow ...see this thread https://www.camaro5.com/forums/showthread.php?t=480088 Last edited by camguynj; 09-18-2018 at 06:31 PM.

09-18-2018, 05:37 PM	#9
christianchevell old school chevy rodder Drives: 2013 2SS/RS Manual,DM exhaust,CRT Join Date: Jul 2012 Location: Oregon Posts: 5,587 View My Garage	You do know the problems with installing and making function the NPP system on a non NPP car and their vacuum activators ? And have a new rear valance? there have been posts on here before. you could just lash them open.....or closed.... __________________ 2021 Wild Cherry ZL1 A10, Sunroof, Data, Carbon, Nav, RotoFab Dry CAI, Elite x2, Borla ATK, Driveshaft shop

09-17-2018, 03:03 PM	#2
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	Few questions 1. Why are you getting rid of your system now? 2. If the NPP is an entire factory welded system, why would you not just put the entire thing in? No sense leaving portions of the 3" system in there.

09-17-2018, 05:04 PM	#4
HOJO Drives: 2014 Camaro SS/RS 1LE 1967 Camaro Join Date: Oct 2013 Location: Fort Wayne, IN Posts: 874	Does that defeat the purpose of the 3 inch if you neck it back down to 3 inch?

09-17-2018, 05:33 PM	#5
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	You can cut anything off you want and adapt the mufflers to your current 3" system. By necking the system back down to 2.5" you pretty much loose all the benefits of the larger pipes, that 3" center section with the x pipe wont do shit. I just think cutting off the 3" stuff to weld on 2.5" NPP mufflers is kind of pointless, just install the entire NPP exhaust and sell your old set up. It will fit up really nice and save you the aggrivation of splicing two different size exhaust systems together.

09-18-2018, 05:46 PM	#10
derieu Engineer Drives: 2014 Camaro 2SS RS 1LE Join Date: Jun 2015 Location: SE Michigan Posts: 230	you wont be losing anything if the only 2.5" part of the exhaust is at the mufflers. If you were super picky about it, cut the muffler open and just replace all of the 2.5" joints with 3" pipe. People use to mod the old z06 bimode exhaust mufflers. Just takes some labor

09-18-2018, 07:49 PM	#11
olblue75 Drives: 2010 2SS/RS Join Date: Dec 2009 Location: Clarksville Tennesse. Posts: 6,064	They are default in the open position. Also remove the resonator and install a X Pipe. __________________ Orange Krush II 1LE Front sway bar, Splitter, shocks and struts, Z28 dual mode mufflers, Intake, UCA Bushings, and Toresen 3.91 Diff. 1 piece DSS Drive Shaft, ZL1/C7 Calipers, and 32mm JPSS Rear Bar. ASC race spec splitter and wicker. 6th Gen M017 Wheels. Stainless Works 1 7/8 LTs. DSE and PAFDT Suspension components.

09-18-2018, 09:01 PM	#12
zz430camaro Drives: 2015 1LE Join Date: Oct 2015 Location: Cleveland, OH Posts: 1,485	The NPP mufflers are good because they dont drone at all really, its a mellow exhaust until you punch it then it sounds good. I just leave em opened up all time, not need to ^uck around with those valves.

09-19-2018, 09:17 AM	#13
christianchevell old school chevy rodder Drives: 2013 2SS/RS Manual,DM exhaust,CRT Join Date: Jul 2012 Location: Oregon Posts: 5,587 View My Garage	Yup I drive with mine open..... and tuned excellent with decel popping not removed. But loved...…….. __________________ 2021 Wild Cherry ZL1 A10, Sunroof, Data, Carbon, Nav, RotoFab Dry CAI, Elite x2, Borla ATK, Driveshaft shop