wow

Wow...great responses (naturally). So if i have this right, the NPP mufflers have a flap that can be controlled by a remote. So is there a difference between NPP muffles from year to year, i.e. NPP mufflers from a say 2009 fit on a 2012? Thanks everyone, Nick

olefam

Hi. What folks on the board have not told you is that the NPP option also has a different algorythm for the fuel injection system. Essentially, to avoid burning valves the computer in our cars enrichens the fuel mix when the valves in the mufflers open. It is the combination of open exhaust and added fuel that gives us the extra 6 HP and the (in my opinion) pleasent "popping" sounds when we get off the throttle.
I'm pretty sure none of the aftermarket systems come with a
reprogrammer for your car's fuel control computer.
Best wishes.
Glen

96GS#007

Never heard that one before. The GM documents say more hp due to reduced back pressure, same as the aftermarket systems have done for years. Never once has someone swapped an exhaust to something with more flow and burned a valve. If that was happening, there'd be a whole lot of aftermarket companies with public relations nightmares on their hands.

These engines are programmed to run very rich from the factory. In fact, much of the gain people get from having tunes done is due to leaning out the mixture in addition to a few timing tweaks.

edcologne

as far as I know:
- base and gs are the same mufflers.
- 08 (first year npp) fit "bolt-on" to stock midpipes 05-08.
- 09 and up are the same, "bolt-on" 09-13.
of course one can swap the midpipes to mix and match...

haljensen

Nobody has ever reported that they were able to change the programming of the ECM to make an add on NPP work exactly the same as OEM. Nobody from GM, no Dealer or no aftermarket tuner has ever changed the ECM to make the NPP work the same.

wow

What is different between the midpipes for 05-08 to 09-13? One is x pipe and one is h pipe (guessing here)? Is there any advantage in performance or sound (or both) to either one? For example, would it be "better" to have the pipes from a 05-08 on a 09-12 or vise versa or neither because there is something even better?

And just for my betterment, is there a desigination for the C6's for 05-08 and another for the 09-13, like a letter or something? Thanks

cclive

I was under the impression that the diff in the NPP was in the area of the pipes that go over the rear axles, but someone will chime in who knows for sure. As for the designation, no, there is no designation difference between '05-'08 and '09-'13, other than just the model year. In truth, the differences all the way from '05 to '13 are mostly minor and are more about GM marketing than true, major substance.

0PalmerPerformance

I will report as doing it. In fact, it is super easy, so easy a Caveman could do it (because I am a caveman). You need the mufflers, the NPP module (can get re-man boxes on Amazon for $75 new), a solenoid, and a vacuum hose. Run it just like the factory does. Power from the fuse in your fuse box that is already there on all C5s (even pre-NPP models), run one wire up to the Class 2 junction next to the fuse box, and you now have full functioning factory NPP. Functions exactly like it was factory installed. The ECM or BCM have nothing to do with NPP, the NPP module does all the magic, and it only needs that one wire to the Class 2 junction to make it all work. Way easier than any aftermarket kit. No switches, no goofy things added to your fuse block, nothing at all, a clean factory install exactly like the factory installed.

ButchN

I'd like to see that "few hundred dollars" upgraded exhaust system.

edcologne

that's my understanding too. the pipe routing over the rear axle is different involving one or both muffler pipes and the according area of the mid pipes.
i'm sure all can be altered by a muffler shop but why bother, i'd rather get the one i want or that fits in the first place.

as far as x-pipe, h-pipe, all the stock ones I saw looked like an h, therefore I assume the stock ones are probably h-pipes, not sure what/how much difference an x-pipe does.
just to add the npp function I don't see a reason to change midpipes.

08 ATOMIC-Z

It can't be done.....if someone on here that says they had it installed like the factory at the dealership I say BS.

haljensen

Caveman; I hate to be the one to tell you this but if you add all the parts you just listed you still don't have "exactly like the factory installed".

The ECM is what controls the 3500RPM opening and that programming is not present in non NPP cars.

Until you find a way to modify the ECM to trigger the exhaust flaps to open at aprx. 3500 RPM without adding any parts you do not have "the same as factory". No aftermarket and no tuner has found a way to mimic factory NPP without adding parts for the RPM opening.

Right now the only aftermarket kit that allows RPM controlled opening is available from http://sunsetorangecreations.com/. Still not the same as factory but very close.

08 ATOMIC-Z

This can not be done at a dealership. If your going to be on here offering assistance you should at least know what your talking about! These newbies don't know and will read your post as if it can and will be pissed when the dealership can't do it.

level6

Thanks atomic-z. I just looked up on ebay and for $69, I found "CORVETTE C6 EXHAUST VACUUM FLOW CONTROL MODULE NPP 15909509" thinking if I bought that I could add factory NPP like caveman said.

disasm

It can be done and I claim to have had it done to my car, although not at the dealership. I would love to prove it to you, how can I do that to your satisfaction?

PalmerPerformance has already replied to this thread earlier - read what they had to say.

disasm

It really can be. But I doubt you would be able to convince a dealership to do it for you.

What is so hard to believe here? Just because there are a thousand aftermarket NPP controllers doesn't mean the factory system somehow does not work. It does work and I have completely 100% factory parts with the addition of a Palmer Performance DashLogic to add DIC and HUD customization and factory NPP control via the mirror switch.

disasm

I think you must be making assumptions like most others. I have done this to my car and there are no issues. PalmerPerformance helped me locate all the right parts and they even have an installation guide. I'm sure they would send you the guide if you asked for it.

The ECM has nothing to do with the NPP functionality. In fact, not only does it not even "know" about it, if you look at the factory wiring diagrams you will see that the NPP cannot even be controlled by the ECM as there is *NO* connection at all.

Instead, there is another module called the EFCM, which connects to the Class 2 junction box (see the post earlier from PalmerPerformance) that does the NPP magic. As PalmerPerformance indicated, this module can be purchased for around $75. And once you have the real factory setup, their DashLogic product can control it for you using the mirror switch.

I would really like to prove this to you, but what would make you a believer? Somehow I doubt that just showing you a picture of my factory NPP mufflers will do it.

96GS#007

I'm talking about NPP in a Box, not the actual exhaust.

Sugar Loaf Bob

Jennie, was going to recommend that Sixtsvn get in touch with you !!!!

HOXXOH

Let's cure some ignorance here with some real facts.

NPP is an option code for the bi-mode muffler system that was first available on '08 C6's. That system utilized 2.5" diameter pipes welded to the mufflers and was connected to an "X" mid-pipe. Inside the muffler, the loud side (with the flap) was a straight through pipe, while the quiet side was chambered and had perforated pipe and fiberglass batting. Internally, the tips were also perforated.

Prior to the '08 MY all C6's had "H" mid-pipes. So any '05-'08 that have the OEM stock mufflers can swap them for the '08 NPP option mufflers and if the '05-'07's so choose, they can swap the "H" for the "X" also.

Then starting in the '09 MY, the angle of the passenger side muffler and "X" mid-pipe changed slightly to allow clearance for a minor unrelated component change. What that means, is that the "X" pipe and passenger side mufflers will not be a no-mod bolton swap on to a '05-'08. A muffler shop may be able to modify them at your risk.

To complicate it a little farther, the '12 and '13 MY used 4 converters instead of 2, so the "X" pipe won't swap with previous "X" pipes.

Now if you're still wanting those mufflers and it's not a direct fit and go, here's a workaround. Simply keep your over-the-axle pipe and cut it off close to the stock muffler. Cut off the bi-mode muffler from it's pipe and discard the pipe. Weld your over-the-axle pipe to the bi-mode muffler and it becomes a no sweat bolton.

One more thing to throw in this mix is the bi-mode mufflers used on C6Z06 and ZR1 cars. The early mufflers had the straight through pipe perforated and the last couple of years were non-perforated. They can also be used by employing the same method as above with a slight difference. Cut the stock 2.5" pipe off the muffler as close to the can as possible and cut the 3" pipe off the Z06 muffler leaving about 3/4" extra on the muffler. Then slip your original pipe in the Z06 stub and weld in place. (The Z06 pipe tapers to 2'5" at the inlet)

Once you have the exhaust system all back in place, you can buy a controller from several sources or make your own. Sunset Orange Creations is a forum vendor and has several options.

To the OP: The OEM method of flap control sucks. That's why the aftermarket stuff exists and most owners of Z06 and NPP optioned cars have added a controller.