Ryoga23

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..

Suns_PSD

It's more restrictive (when closed) and it won't hurt a thing.

Ryoga23

Excellent. What I was hopping to hear.

Thanks

schpenxel

Mine would go quite rich at WOT with the flaps closed for whatever that is worth

Grimlock13

Looking a a stock LS3 (kinda) car with the valves forced closed, the dyno graph shows a big loss (40 HP peak) in power.

HOXXOH

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.

Grimlock13

I did not realize that.

schpenxel

The ECM doesn't even control the flaps.. so why was the test flawed?

HOXXOH

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.

schpenxel

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.

0DashLogic

You are correct, in fact you can install the NPP system on a non-NPP car the exhaust works exactly like factory. I don't think the exhaust module has an effect on the PCM at all. My conclusion to this is that a factory non NPP muffer flows much better than an NPP in closed mode. Even running in factory stock form, the closed valves hurt even low end power, why would we assume it would not keep hurting as exhaust flow goes up?

schpenxel

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)

0DashLogic

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.

Tennis_pr0

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.

0DashLogic

NPP is always open at WOT, I am not sure what you are trying to say?

Suns_PSD

Where is the NPP controller? I sold my NPP and I want to pull those parts and send them to the new user. Can I just remove it and that's it?

Tennis_pr0

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.

Seadawg

I have a stock (kinda) LS3 (meaning it only has headers and a tune), and I routinely run with my NPPs forced "closed" by the Dashlogic device, just because I don't want to draw loud attention to myself most times.

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.

schpenxel

http://www.tonkinonlineparts.com/sho...roduct=6317892

021

0DashLogic

In one of the cubbies in the hatch area. The solenoid and reserve tank is under the car