NPP performance with valves open and closed

[BriteCrawler]

Originally Posted by christianchevell

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...

I can't believe I spent the effort to actually read part of and decode your post, but if you're paying more than $25-$50 for 3 -baseline- pulls, you're being screwed. Hard.

Signed, done literally hundreds of dyno pulls in my life.

[bluerayone]

CamaroFred, I see your 5th gen Resonator cutaway is from a non NPP exhaust. Still the holes are interesting as I would have suspected the inlet to empty into the resonator for maximum sound reduction not into a pipe passing through it. I have similar holes in my 5th gen NPP muffler / resonator however when the straight pipe is closed off all exhaust must travel through these perforations to reach the other pipe. What's your view on the capacity of these holes in the straight pipe ---do they have enough capacity to to equal 2 1/2 diameter pipe?

[CamaroFred]

Originally Posted by bluerayone

CamaroFred, I see your 5th gen Resonator cutaway is from a non NPP exhaust. Still the holes are interesting as I would have suspected the inlet to empty into the resonator for maximum sound reduction not into a pipe passing through it. I have similar holes in my 5th gen NPP muffler / resonator however when the straight pipe is closed off all exhaust must travel through these perforations to reach the other pipe. What's your view on the capacity of these holes in the straight pipe ---do they have enough capacity to to equal 2 1/2 diameter pipe?

There appears to be more than enough.

A 2.5" pipe has 4.9 square inches of opening.

It's easier to stab at the hole size on the 5th gen being 3/8", and there are 12 columns and I am guessing 6 rows. Which would be ~7.9 square inches (4.5" pipe). But I think there are some rows on each side of the baffle, so probably more.

The 6th gen holes are smaller but there are more of them, 36 columns X 9 rows. If I assume the holes are 3/16" there would be 8.9 square inches of opening (5.7" pipe).

I would be interested to see a 6th gen non-NPP muffler. It may be quite similar to the 5th gen.

[bluerayone]

I have seen charts on max HP that you can run through different diameter pipes. 2 1/2 seems generous compared to tailpipes on classics from the late 60s , 70s. I walked by an early 70s cadillac eldarado last night that had 2in pipes (or smaller) and they looked stock. The exhaust coming to the resonators on the Camaro looks to be 3 in. I think they set it up like that knowing many will be supercharged. I have also read that oversized pipes can have a detrimental affect on the scavenger effect (don't know if the scavenger effect still applies to modern computer controlled engines found in the Camaro).

[CamaroFred]

Originally Posted by bluerayone

I have seen charts on max HP that you can run through different diameter pipes. 2 1/2 seems generous compared to tailpipes on classics from the late 60s , 70s. I walked by an early 70s cadillac eldarado last night that had 2in pipes (or smaller) and they looked stock. The exhaust coming to the resonators on the Camaro looks to be 3 in. I think they set it up like that knowing many will be supercharged. I have also read that oversized pipes can have a detrimental affect on the scavenger effect (don't know if the scavenger effect still applies to modern computer controlled engines found in the Camaro).

I gotta believe the perforations in the pipe smooth the airflow.
When a pulse of exhaust moves through the pipe some of it is allowed to escape through the perforation, which builds pressure in the surrounding chamber. When the pulse ends pressure from the chamber enters the pipe to fill the void to maintain a constant flow, which will increase the scavenger effect.
Without the perforation and chambers a V8 running at 2000- 2500 RPM would have a tone of 133-166Hz. Your dreaded drone. Instead you hear a whoosh.

When the engine is running at a higher speed the pulse frequency increases so there is almost a continuous flow, the pressure in the chamber equalizes to the pressure in the exhaust pipe and therefore the exhaust runs straight through to the tailpipe.

So like the Helmholtz chambers you see on your stock intake, you get reduced noise and greater power.

The size and length of the exhaust tips also has some effect on the amount of air that can pass throught the exhaust system. The greater diameter allows the escaping gasses to expand without disruption, which reduces their pressure, which increases the draw to the muffler (scavenging).
I'm sure the length on for tailpipe is also computed according to engine output.

If you can accept the concept that the engineers can tune the exhaust for any volume, at any speed, for any motor,
Then you need to ask, "Why did Chevy make the stock exhaust so quiet?"
1. Legislation
2. Reliability
3. Buyer preferences.
4. Cost. This is when the engineers chip in.
If we add these perforations and baffles to the exhaust pipe they will have less restriction than the Mercedes for 1/10th the cost and exceed our goals.

All the Camaro engineers.

[2010reddevil]

A gas pulse flowing from a smaller area to a larger area does not scavenge more, it actually slows down and hampers flow. You want high velocity without making a choke point. And I bet you anything that the tips make absolutely no performance benefit one way or the other, purely cosmetic. Most oem exhaust systems are designed from a cost stand point and noise emissions. There are only a handfull of cars made that have a really good sounding oem exhaust system and that include the Camaro/Corvette NPP setup as well as the Shelby GT350 and 500. Some Mercedes sound really good too stock.

[christianchevell]

Blue ray your lost...LOL: there are never four pipes open except when its switching temporarily. Dual mode is on the Camaro straight through at idle then on at about 2500 -3500 rpm I forget or basically when you get on it if its in stock mode. A switch allows you to keep one set of pipes open or closed. And that stock trash can out back is what I had on the L99 and I know the suitcase resonator did not help..LOL but it was a vert and therefore more sound makes its way in....And the Camaro exhaust is very similar to the corvette exhaust when it comes to the NPP exception at start up on some years. That annoying resonance I suggest is you lugging the engine..... LOL as In one particular rpm I have low rattle from the harmonics and it goes away fast and most likely its from lugging low and the vibration rattling on the system.

[CamaroFred]

Originally Posted by 2010reddevil

A gas pulse flowing from a smaller area to a larger area does not scavenge more, it actually slows down and hampers flow. You want high velocity without making a choke point. And I bet you anything that the tips make absolutely no performance benefit one way or the other, purely cosmetic. Most oem exhaust systems are designed from a cost stand point and noise emissions. There are only a handfull of cars made that have a really good sounding oem exhaust system and that include the Camaro/Corvette NPP setup as well as the Shelby GT350 and 500. Some Mercedes sound really good too stock.

That must be why the car looses 45-50HP with the NPP closed.

[CamaroFred]

Originally Posted by christianchevell

Blue ray your lost...LOL: there are never four pipes open except when its switching temporarily. Dual mode is on the Camaro straight through at idle then on at about 2500 -3500 rpm I forget or basically when you get on it if its in stock mode. A switch allows you to keep one set of pipes open or closed. And that stock trash can out back is what I had on the L99 and I know the suitcase resonator did not help..LOL but it was a vert and therefore more sound makes its way in....And the Camaro exhaust is very similar to the corvette exhaust when it comes to the NPP exception at start up on some years. That annoying resonance I suggest is you lugging the engine..... LOL as In one particular rpm I have low rattle from the harmonics and it goes away fast and most likely its from lugging low and the vibration rattling on the system.

Interesting.
I thought the valve on the Camaro NPP only opens/closes the straight through while the muffled pipe is always open.

[2010reddevil]

Originally Posted by CamaroFred

That must be why the car looses 45-50HP with the NPP closed.

If you're s/c, I could see it being somewhere in the area of 20-30whp. N/A, no more than 5-10 at worst.

[bluerayone]

christianchevell, I am not as you lost as you think, I believe 4 pipes are open the most of the time on the Camaro NPP,. Engineers at Palmer engineering (dash ogic) estimate cutouts are open about 70 percent of the time, from the sound of it Id say its about right unless you do a lot steady highway driving then they're closed otherwise from start up, getting to speed, down sifting, the cut outs are open.

[bluerayone]

2010 reddevil, I agree -- S/C will increase the likelihood of hitting the limit on a restricted exhaust if the cutouts are closed and your forcing exhaust though the perforations to reach the two remaining pipes. Also, agree that a stock LS3 like mine loss is probably negligible and nothing to worry about. Still looking for statistical evidence , track sheet, or Dyno pulls for a camaro with stock NPP system , no mods, and open and closed runs.

[2010reddevil]

The outer tips are the ones with the valves. If they are closed, then the exhaust is routed through the muffler body and the inner tips. If they are open, most of the gasses follow the path of least resistance and go through the outer tips and a small amount still flows through the muffler body and exits the inner tips as well. It's either one set of openings are open, or they all are, not one set and then the other.

[christianchevell]

Holy jumping Jehosaphat if you can pay for pulls at my tuner for that $25 you just go ahead.... For him to hook up a car in his schedule its usually $550 for a tune which includes however many "pulls" and can involve hours with Gm software and hard ware and a couple lap tops and HP tuners along with the dynos display and hooking up to varied sensors on the engine and strapping the engine down with air flow trough the front. But hey what does one guy know with just a couple electrical engineering degrees and a waiting list a mile long.

Sure hooking up someplaces can be cheaper, and some tunes can suck. I know when I got my last retune which involved many pulls for $250 a corvette a c-7 was there getting well over 150 more HP than the "tune" the superchargers installer gave it, and the guy drove hundreds of miles with it trailered to get there.
I have thought of giving it a dyno run at a car show just for the fun of it, it involves giving them some money, they hook it up and go hey they made Blank HP! NEXT.... thanks for the money.

Maybe someday I will do a dyno run and have sheets printed to just dispel this myth that its so restrictive, or god forbid take a movie of my exhaust opening and closing in the cold to show...hey theres a reason one tips all black and covered in carbon compared to the other ....And I can turn mine off and on. Any valve leakage that's just coincidental. But for me to put out the money for dyno its going to be with other major work because .....Its not cheap. Check around, a few pulls for info sake is way different from a tune.

Here I could hook up for $100 for three pulls at shop, they use a dynojet and know nothing about HP tuners, or the stock GM hardware/software that interfaces with the ECU, let alone how to interpret and modify the data to the desired effects by altering the AFR or timing and such/ now give them a 56 chevy with a 350 and carb and distributor sure they can jet it and do nice things but for a majority of shops its still the stone age. Smart shops send customers to other shops when they are in over their head. We do not have cut outs, cut outs are a mechanically or electronically hole in the pipe basically that can be opened to dump massive sound and exhaust usually up toward the headers. That's what I think of when I think of "cutouts".

And once again the NPP dual mode exhaust on the Camaro is open at start then open again after reaching enough vacuum/the RPM to opne them up unless altered by a mild to wild or Forza switch or home made switch and the 6th gen have a electric switch.
You can feel the exhaust by the pipes also.

And enough people on here have paid $500 for tune on here.....a couple runs is done by Billy Bob unless your dealing with a helper not the Master at a shop or unless your just seeing what it makes easy breezy.
May this pic say it all: sure its a Corvette, how much exhust do you think is flowing out the closed tip? Maybe dash logic thinks its 70%,( most likely a estimate of the system operating as designed open and closed), LOL ,and call it a cut out : but for most of us its diverted exhaust or pretty dang straight through.

http://www.corvettemods.com/assets/i...haust_tips.jpg

The muffled pipe is always open it just is easier to go straight through like 10000% , and BTW I thoroughly researched Before I picked my Tuner as he is about the best in the NW Tommy Wong used to be a electrical engineer for Boise Cascade, he gets what other shops destroy, screw up, the factory warranties fail to cover because dealers suck and has seen plenty of stock cams on stock cars fail with roller lifters from top of the line Corvettes, Cadillacs, and Camaros to just changing out the ring gears in a old cutlass or installing supercharger after super charger on big money builds. I trust his judgement and Pay for his time and he is cool in my book, but what do we know we are just old hot rodders. If anyone here has a question no one can answer I can get it from him if I can get his attention for split moment, and highly recommend him, and yes have seen him turning cars back to stock for people who screwed the pooch and have to go for warranty work.

Does not mean he installed it......Sitting next to his pile of 100s of cam shafts he stocks he barely has room to breath between constant streams of phone calls and customers just wondering in, that's what successful means. I know I am successful in my field and have a hell of a time getting breathing room from everyone elses projects for my own! But I am a go too guy and that's why I get the big bucks and should be more but I don't want to be a boss, because creativity is what its all about and we only have so much time on this earth. Talk on the other hand well its cheap, and opinions are like........

Last year about September on his facebook page that's my Camaro, he does not update his page much as well he is busy as hell, but hey theres nice videos on his page cool stuff thought I would share ...nice exhaust video etc... I am not the most knowledgable but I try to help, and yes Crap happens...LOL I have video on his page somewhere with my first engine made 491 hp and 448 torque with the TSP 235/239 headers HFC CAI and a tune.

https://www.facebook.com/Wongs-Perfo...-115667950915/

Oh and BTW I saw that f100 his customer had at SEMA when he was tuning it. Very nice, yes Fords need Chevy power..LOL