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Camaro V8 LS3 / L99 Engine, Exhaust, and Bolt-Ons Bolt-Ons | Intakes | Exhaust

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Old 04-22-2013, 09:18 PM   #1
asprex
 
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Dual mode exhaust

Could someone with a dual mode exhaust post pictures of the vacuum valve and vacuum source for the muffler valves. I'm installing the NPP exhaust on my 2012 ss and have not seen a factory install. Thanks.
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Old 05-07-2013, 03:59 AM   #2
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I added NPP Dual mode exhaust to my new 2013 as well. Adding the new pipes was the easy part.

However, to control the flaps, the dealer was forced to use an aftermarket "NPP in a Box" vacuum actuator (sells for about $170.00) since it could not replicate the factory option. It is a simply on/off set up you control by key fob, or you can also program the switch to your homelink garage door opener buttons.

Apparently, while NPP is an easily installed $895.00 option at the GM assembly line, adding it after production would require not only VERY expensive GM vacuum parts and electrical relays, but also computer software flash modifications to both the engine control and fuel management systems - which they could not do, even as a GM dealer.

Let me know if you find out differently, as they spent nearly a week researching this for me before going with "NPP in a Box". I would have loved to install the GM factory "automatic" function, but NPP was the 1 option my car did not have.

The one draw back to the NPP in a Box is that closed flaps is too mild, and open flaps in normal driving is just too loud, with huge low end "drone" at highway speeds. They sell aftermarket flap "adjusters" for $25.00 so you can close only 90% flaps, for example. They are simple clamps you attach to the actuator rods to stop them from closing all the way when vacuum is applied. You can adjust the amount of flap closing by the chosen placement of the clamps on the rods.

Last edited by ahesq; 05-07-2013 at 04:07 AM. Reason: Adding more info.
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Old 05-07-2013, 01:05 PM   #3
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Quote:
Originally Posted by asprex View Post
Could someone with a dual mode exhaust post pictures of the vacuum valve and vacuum source for the muffler valves. I'm installing the NPP exhaust on my 2012 ss and have not seen a factory install. Thanks.
The back of the LS3 intake manifold has a vacuum port

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Old 05-14-2013, 09:06 PM   #4
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Does anyone know where the L99 vacuum port is if any?
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Old 05-14-2013, 09:20 PM   #5
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Does anyone know where the L99 vacuum port is if any?
I didn't think the auto came with dual mode?
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Old 05-14-2013, 09:38 PM   #6
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Auto didn't, however I have the opportunity to buy a complete NPP catback and want retro fit it to my 2013 L99
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Old 05-15-2013, 06:38 AM   #7
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I was under the impression there was more to the hook-up than vacuum lines. Thought I read somewhere in another thread about electronic module and error readings.
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Old 05-15-2013, 08:43 AM   #8
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Zorn: Yes, I was looking to use the after-market "NPP in a Box" setup but not sure if the L99 intake manifold has the same vacuum port on the back like the LS3 one.
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Old 03-18-2015, 12:49 AM   #9
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I just purchased a NPP compete exhaust system. I have a 2012 SS automatic though. Anything I need to know before installing this system?
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Old 03-18-2015, 03:37 AM   #10
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I capped my vacuum line after sc install and it sounds great. No need for dual mode lol
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Old 03-20-2015, 08:11 PM   #11
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Any full time vacuum source should work so long as you aren't upstream of any sensors. I'd hook the exhaust up and just leave it open all the time - hook the vacuum line up if you go in for an inspection and have noise requirements or get one of the aftermarket switched controllers. The flaps will always be open on startup until the engine builds vacuum though.
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Old 03-21-2015, 06:19 PM   #12
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I have the NPP but I pulled my fuse so it don't work. Sounds better without the dual mode. No sense in getting NPP I wouldn't think unless you like the look.
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Old 03-23-2015, 12:20 AM   #13
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Quote:
Originally Posted by Wollmank View Post
I have the NPP but I pulled my fuse so it don't work. Sounds better without the dual mode. No sense in getting NPP I wouldn't think unless you like the look.
The NPP literally wakes up, in significant increments might I add, with every single bolt on mod that you throw at it, lol.

That fuse will be going back in short order after one installs LT and off-road pipes.

Not yet some might say? Well then add a cam for good measure, and particularly in cold weather when the air is nice and dense, you will be the first in line to buy a NPP controller switch for permanent shutting off of the flaps when driving around conservative areas.
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Old 03-23-2015, 06:58 AM   #14
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The NPP literally wakes up, in significant increments might I add, with every single bolt on mod that you throw at it, lol.

That fuse will be going back in short order after one installs LT and off-road pipes.

Not yet some might say? Well then add a cam for good measure, and particularly in cold weather when the air is nice and dense, you will be the first in line to buy a NPP controller switch for permanent shutting off of the flaps when driving around conservative areas.
You are not kidding sir!!!

After the header install I set mine up to be able to keep them closed, just as a courtesy for my neighbors.

After the cam install , it was a requirement to be able to tame the beast. You would swear they are not the same exhaust at this point, there is no longer a resemblance to the much more tame factory sound.

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