NPP closed back pressure
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Joined: Mar 2010
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From: Houston TX
NPP closed back pressure
After a lot of digging regarding the NPP systems on the forums I'm left with a (hopefully) simple question I'd like clearly answered. But before that a quick backfill on what I'm wanting.
I have an 05 vette running a magnacharger with headers and a Borla exhaust system. Problem is I'm frequently making 4 hour each way road trips and it's time for more quiet time. To be honest I'd rather hear more of the music and occasional charger whine than exhaust these days as sacreligious as it may seem.
I've been offered a potential to swap my Borlas out for someone else's NPPs, but of course I'm not NPP optioned so I need to get the box to retrofit. Timing is crucial to for this, so I had planned to just temporarily wire the valve closed for the quiet setting for a couple weeks until I could install the needed extras for mild to wild etc.
So the question is this, is there any real risk of damage due to back pressure if I run this more ,restrictive configuration - I assume that valve closed is more restrictive than regular stock exhaust..
I have an 05 vette running a magnacharger with headers and a Borla exhaust system. Problem is I'm frequently making 4 hour each way road trips and it's time for more quiet time. To be honest I'd rather hear more of the music and occasional charger whine than exhaust these days as sacreligious as it may seem.
I've been offered a potential to swap my Borlas out for someone else's NPPs, but of course I'm not NPP optioned so I need to get the box to retrofit. Timing is crucial to for this, so I had planned to just temporarily wire the valve closed for the quiet setting for a couple weeks until I could install the needed extras for mild to wild etc.
So the question is this, is there any real risk of damage due to back pressure if I run this more ,restrictive configuration - I assume that valve closed is more restrictive than regular stock exhaust..
Race Director
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
That was a flawed test you're referencing, since the valves were not mechanically closed, but electronically closed and that apparently affected other areas of the ECM.
Melting Slicks
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Race Director
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From: Peoria/Phoenix AZ
C6 of Year Finalist (performance mods) 2019
It does when it's the OEM system, which is what that dyno test was comparing, as there is no other way to determine 3,500 RPM and WOT. The flaps on that one questionable pull were closed with the Dashlogic device which accesses the ECM in an unknown manner.
When GM runs a controlled engine dyno test and only gets a 6 HP difference at 5,900 RPM, but someone with a product to sell gets a 40 HP change on a chassis dyno, you just know there is more involved than some muffler chambers. Nobody leaves that much HP on the table because of a muffler.
When GM runs a controlled engine dyno test and only gets a 6 HP difference at 5,900 RPM, but someone with a product to sell gets a 40 HP change on a chassis dyno, you just know there is more involved than some muffler chambers. Nobody leaves that much HP on the table because of a muffler.
Race Director
Joined: May 2004
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From: Raleigh, NC
St. Jude Donor '15
No, it doesn't. There is a separate exhaust flap or NPP controller even from the factory that connects to the CAN bus and to the exhaust solenoid. Based on info it gets from the CAN bus, i.e. RPM/throttle, it opens/closes the flaps on it's own.
I'm not saying it gains or loses HP or whatever.. just saying that the ECM doesn't control the flaps, there is a separate controller that does that, even in stock NPP vehicles.
I'm not saying it gains or loses HP or whatever.. just saying that the ECM doesn't control the flaps, there is a separate controller that does that, even in stock NPP vehicles.
Last edited by schpenxel; Mar 29, 2016 at 12:48 PM.
Former Vendor
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No, it doesn't. There is a separate exhaust flap or NPP controller even from the factory that connects to the CAN bus and to the exhaust solenoid. Based on info it gets from the CAN bus, i.e. RPM/throttle, it opens/closes the flaps on it's own.
I'm not saying it gains or loses HP or whatever.. just saying that the ECM doesn't control the flaps, there is a separate controller that does that, even in stock NPP vehicles.
I'm not saying it gains or loses HP or whatever.. just saying that the ECM doesn't control the flaps, there is a separate controller that does that, even in stock NPP vehicles.
Race Director
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From: Raleigh, NC
St. Jude Donor '15
Thanks, I added the factory NPP controller to my car actually.
I was the guy that sent you guys the info on all the connectors you need to add the factory NPP controller to a non-NPP car.
I don't have a log to show, but I remember when I forced the flaps closed all the time it would go extremely rich at WOT. That told me it was flowing less air at the same amount of boost/fuel, which would = rich (was in SD mode, no MAF)
I was the guy that sent you guys the info on all the connectors you need to add the factory NPP controller to a non-NPP car.
I don't have a log to show, but I remember when I forced the flaps closed all the time it would go extremely rich at WOT. That told me it was flowing less air at the same amount of boost/fuel, which would = rich (was in SD mode, no MAF)
Former Vendor
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I don't see how posting that sheet sells anything. If you want peak power and care about nothing else, pull the fuse. The graph was posted for informational purposes only. Too bad we didn't wire the valves closed to show that the DashControl had zero effect on the outcome. At the time I never expected it would be so controversial, hindsight I guess.
Racer
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By the time the exhaust gases reach the mufflers I don't think there would be any difference in back pressure whether the flaps are open or closed. That's why when you add a simple axle back exhaust you don't see any power gains, because that far down the exhaust system is not going to be putting any restriction due to back pressure on the manifolds.
I know there are plenty of people running crazy high HP cars with the NPP's and I've never heard of it being an issue.
I know there are plenty of people running crazy high HP cars with the NPP's and I've never heard of it being an issue.
Former Vendor
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Racer
Joined: Feb 2015
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OP was asking if the NPP exhaust would cause an issue with back pressure. Yes the flaps open above a certain RPM, but I was answering his question specifically when the flaps are closed, not opened. His question was about back pressure when the flaps are closed.
Safety Car
Joined: Nov 2006
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Seat of the pants, I cannot tell any difference between fully open NPP and fully closed NPP. Even grabbing the gears, it feels about the same amount of wheel spin too.
So my bet is, it is not much of a HP loss between full open NPP and full closed NPP on an LS3, certainly not 40 HP
Now if I get to installing a supercharger, I'll monitor my AFR and compare to see what it is really doing to the engine, before I run fully closed for any period of time under load.
Race Director
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From: Raleigh, NC
St. Jude Donor '15
Former Vendor
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