NPP performance with valves open and closed

[bluerayone]

I have a 2015 2SS/RS with NPP. I know I am in the minority, however , my personal sound level preference is between stock mufflers, and stock NPP so I run with the valves closed most of the time (although I know there are systems to close the valves from the seat, I chose to clamp them at the actuators which I can easily open or close in a minute on those rare times I chose to run open).

Here is my question: I know there is debate on whether the valves actually add 5-6 horse power over the stock mufflers when open as the HP gain is advertised with the vett but not the camaro -- so some speculate the open valve is just sound enhancement). My concern is how much horsepower and torque do I lose over stock mufflers running with NPP valves closed.

There is a post out there showing someone did dyno pulls with stock NPP valves open/closed showing a 45-50 hp decline with valves closed using a gadget from Palmer engineering to close the valves. I doubted that type of power loss until I saw another post of cutaway of NPP system used on 2016 (2016 uses two mufflers housed in a single unit for aero efficiency - but seeing the inlets on my mufflers align to the outer pipes I bet the concept is the same, perforated holes on the out pipe allow exhaust to reach inner pipe when involves closed. My point, NPP looks inherently more restrictive than stock muffler with valves closed.

Has anyone with a Gen 5 with unmodified stock NPP done dyne pull or track times running with valves open closed. My interest is on power loss with valves closed.

[Aug]

Really, if there was 45-50 HP "gain" or loss, it would be reflected in the specs of the car; GM would not miss such a marketing opportunity. I would bet even 5 HP they would advertise.

Further, 5-6 HP loss might be noticeable at the track, but on the street, even with spirited driving, you would not be able to tell. I have the Forza 3 way on mine, and I don't notice any performance difference when the valves are closed in quiet mode.

[bluerayone]

Thank you Steve. I know most are concerned with the marginal ( at best )5 hp increase running with valves open and most will reply to my post with its a 5hp loss stupid if valve are closed. I interpreted the 5hp increase claim as a benchmark against a stock non NPP muffler setup and not someone like me (or you) perhaps misusing the NPP system forcing the two by pass valves closed at all times. Under these conditions I wondered if a stock NPP might be more restrictive than a stock muffler setup and perhaps account for large decrease in power similar to the owner who posted his dyno runs using a palmar engineering dash logic to close the valves. Of course we know palmer overrides the camaros on board computer to control vacuum to close the valves and some have speculated that in the process they may have altered other computer variables that produced such a large variance in horsepower and torque with valves open and closed. The last line of your reply was most welcome and responsive to my post, you feel no difference between the two modes and surely you would have picked one up if 45-50 hp/torque loss was true. That said I just thought I'd reach out to see if any gen 5 NPP owner have empirical evidence (DYNO or Time Slips) for open and closed runs.

[bluerayone]

Here is a link to a cutaway of a NPP system on a Gen 6 camaro

http://www.camaro6.com/forums/showthread.php?t=427570

I have a gen 5 with separate NPP mufflers, however my muffler inlet aligns to the straight (outer) pipe as it does in the GEN 6 NPP cutaway so i bet the internal design is similar

Here is a link to two dyno pulls, open and closed, albeit on corvette using palmer engineering dash logic to hold valves closed at all times.

http://www.corvetteforum.com/forums/...en-vs-oem.html

At first I though it was ludicrous to have 45hp power loss with two valves and I dismissed the test results thinking dash logic may have alter other engine variables in the process of closing the valves.

After I saw the NPP cut away though and if the straight pipe valve is closed, exhaust needs to travel through perforations in the straight pipe and through a convoluted path to reach the inner pipe it made me think back to the corvette dash logic pull results and start to wonder if stock NPP is more restrictive than stock mufflers when on by-pass valves are closed.

[Aug]

Originally Posted by bluerayone

Here is a link to a cutaway of a NPP system on a Gen 6 camaro

http://www.camaro6.com/forums/showthread.php?t=427570

I have a gen 5 with separate NPP mufflers, however my muffler inlet aligns to the straight (outer) pipe as it does in the GEN 6 NPP cutaway so i bet the internal design is similar

Here is a link to two dyno pulls, open and closed, albeit on corvette using palmer engineering dash logic to hold valves closed at all times.

http://www.corvetteforum.com/forums/...en-vs-oem.html

At first I though it was ludicrous to have 45hp power loss with two valves and I dismissed the test results thinking dash logic may have alter other engine variables in the process of closing the valves.

After I saw the NPP cut away though and if the straight pipe valve is closed, exhaust needs to travel through perforations in the straight pipe and through a convoluted path to reach the inner pipe it made me think back to the corvette dash logic pull results and start to wonder if stock NPP is more restrictive than stock mufflers when on by-pass valves are closed.

I don't intend to be debating this, just my thoughts since this is all guessing without a Camaro Gen5 dyno run using a non dashlogic controller or other mechanical method to control the valves, but with that said, even with my valves closed in "quiet mode", the sound is louder than the stock automatic transmission SS cars, so with that, I would have to think the NPP with valves closed still is at least as free flowing as stock non NPP. Again, if there was that much of a difference in HP, it would be pretty obvious IMO. Of course, I have no data - except my butt-dyno

[2010reddevil]

My friend with a s/c C6Z and the NPP system has a dyno verified 54whp loss with valves closed. I will say that with it being cammed and all, it's very stealthy when closed. With it open, not a chance in hell.........lol.

[gajagfan]

It was discussed here a few years back to be about 3 HP on the Camaro's. No way in hell (and I don't care what anyone's dyno sheet says) is it 50 HP. NO WAY IN HELL. For that to be the case, it would have to be the most restrictive part on the car exhaust (which in stock form, I do not believe it is), and people would be experiencing massive HP Gains from header/loss of cats/nearly straight pipe exhaust, and they are not. I can go with the 3 HP, but that is about it. I think Vette guys found about 6 with theirs.

[2010reddevil]

When you're pushing nearly 700 rwhp through a closed NPP system and then it's opened, I can see it being that much power. On a basic or even cammed n/a LS3, nah. I'd say under those circumstances, at most 10 rwhp closed.

[BriteCrawler]

3-5 HP is going to be within the margin of error for most Dynos (dynojet advertises a 1% margin of error) and most certainly not detectable in the "butt dyno". You're not going to be able to reliably measure that.

Spend the 1 hour and $25 for 3 pulls and see what it says.

[bluerayone]

My LS3 is stock It seems logical to me that the more RWHP pushed with a super charged motor might show a bigger difference in pulls with valves open and closed. There is the old saying, it not a restriction until it is. Not to be labor the point, but looking at the NPP cutaway above and seeing the straight pipe is the only connection to the inlet and if the valve is closed the exhaust must be forced through perforation in the straight pipe to reach the remaining outlet I could see how that system might become restrictive at mid to high rpm ranges with resulting power loss. On the flip side, I have read plenty that that changes from the cat back produce marginal changes at best because other exhaust part like catalytic converter are much more restrictive. It may come down to spending $25 for a few pulls just wanted to check with you all first.

[christianchevell]

I have a Npp exhaust on this and my last engine neither felt any worse for the use of the exhaust by letting it go closed as in stock form it does go between the modes! , even though now I have a Forza threeway switch I use it and can make very nice decel popping from the exhaust down shifting or letting off it from the fuel cut off... and sound like I roar when I want to and then nice to be quieter when I want it and I assure you its not a 50 hp drop form a little bit more in back pressure its most likely problems with the programming and on my second Camaro can attest that even with the valves closed it sounds nicer than stock non NPP l99 exhaust. SO what ever...LOL and god forbid you put a muffler on it you'll loose 50 HP and flying Monkeys will pass you flipping you off.....GTFOT

That's a 2016 NPP pic with a totally different muffler set up than our gen 5's BTW and still it would not loose power that much even being that much more convoluted its a sports car.... And where I get tuned its more like 250 for a couple pulls if your already tuned, 550 tuned on the dyno HP tuned with GM software also hardware... Time is money and a "guy" who earns $100+ bucks a hour for a shop with his dyno being more .....and hooking it up and doing it your going to pay to help as there is dyno maintenance and it does so cost like 25k for a good Mustang dyno and someone has to pay the bills...Restrictive LOL Pushing mega horse you worry about more restrictive and 2 1/2 " is what most us old rodders had to upgrade too...., and 3" a pain to bend ,or find a shop who will do it to custom make exhaust often as its not a Midas thing usually avoid them ....and mufflers and then have it straight off 3" collectors. Not my first rodeo , and it can gain 5hp I would say with better flow, but its not going to drop 50 LOL or it would not be on your car and you can bank on that..... LOL I have long ago seen the NPP interior cant find a pic right now but hey its straight through or perforated pipe... not a plumbing nightmare just straight back out the tip. https://www.bing.com/images/search?q...ro&FORM=RESTAB

[CamaroFred]

For reference here is a stock 5th gen muffler.
There is a baffle under the ridge left in place, and I believe there is also a hole in that baffle between the pipes that go through it. As well as more perforations under the bit of insulation near the exit.



Stonehenge was built thousands of years ago with enormous blocks of stone and has acoustic characteristics (resonations and clarity) that rival concert halls built today.
If they could do it then, surely we can do it today.

christianchevelle: keep in mind the super resonator on the L99 made a big difference in the sound from the LS3.

[bluerayone]

Yes, I acknowledged when the cutaway link was off a 2016 and as you point out I have separate mufflers and probably glass packs at that not much sound reduction when valves are closed but its a help. I will say the inlet seem to align to outer pipe like the 2016, and if look through the straight thru pipe I can see hole leading me to believe its a similar 2016 design albeit two separate muffler rather single unit. Its also agree that the ECU modulates the vacuum to close the valves, but in stock form they close very little, maybe between 1200-3000 RPF or thats it. Palmer engineering , maker of dash logic, estimates the camaro's NPP is designed to be open 75 percent of the time (unlike the Corvette NPP that is closed at startup and does not open until 3k rpm - its less intrusive). Also agree that even closed it sound better then stock, quite loud actually, and has some have pointed out NPP gets louder by the mile up to about 1500 miles as the muffler get glazed (or seasoned) and less efficient at sound dampening. In fact my exhaust is as loud now on two pipes as it was on 4 pipes when it was new. To me, and I realize it a personal thing and I in the minority on this, the exhaust sounds course on 4 pipes (as two are straight though, generate a sound similar to losing a muffler in the old days) , and the exhaust generates an annoying resonance when going through the gears thats is not pleasant. So although there are a couple thing about having 4 pipes open the good out weighs the bad.. Again I realize its a personal taste, and most will say the louder the better. The Camaro with NPP is the loudest stock car I have owned. I had a 2005 Corvette before this, the Camaro with NPP is much louder.

[bluerayone]

Thanks CamaroFred for the 5th gen cutaway .. about what I suspected.