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Let me preface this with - I'm probably a bit older and/or more boring than most on the list. The car is meant to be daily-driver-*capable*.

I ordered and had a local shop install ZL1 Corsa XPipe and NPP mufflers. Wanted a bit more volume, rolled the dice with some $, it isn't what it was with the axle-back on my Gen5. Probably a sunk cost now. I still have the stock parts at the mechanic's; but not the boxes. I may pay again to swap the old muffler back on but keep the XPipe, and resell the mufflers.

1. Stealth/slow driving or idle, quieter than stock
2. Sport/Track - improved muscle-car idle. Biggest improvement.
3. Backfire - esp under an overpass, sounds like an unsuppressed machine gun (this is bad).
4. WOT in all modes - NPP seems to always open - crazy-loud. "Come arrest me I'm speeding".
5. Stealth/spirited driving with gas pedal down/RPMs high - it starts quiet than transitions into a loud ROAR. This hurts, there's no true stealth mode.


The most painful is I no longer have (5) - any ability to do spirited *quiet* driving, i.e. if I accelerate on the expressway it seems NPP always opens at some point even in stealth.

Question: Has anyone ever done anything with a reprogram or a remote switch on the fuse etc. to selectively *disable* NPP valve from opening? (4) - WOT muffler bypass - not sure if I could get used to it.

However, starting to wonder if I'd ever actually want the valves to open.

Any other thoughts on the matter appreciated.

[Megahurtz]

You have two choices. Put the stock exhaust back on or stop being scared of the police. It's in your head that every police officer in Texas hears you when you drive.

It would be an awful huge waste of money to keep the valves closed on your expensive Corsa exhaust. Additionally, it can potentially cause damage to the engine if you close the valves permanently and go full throttle. I wouldn't recommend trying that at all. If you manually disable the valves with a switch, you will get a Check Engine Light.

Depending on the model/year, HPTuners has defined CCM access which allows you to program the valves to operate how you want. But again, keeping them closed at WOT can damage the engine.

Sorry if this isn't what you were hoping to hear. If you can't accept the loud, I would recommend putting the stock exhaust back on and selling your Corsa to recoup some of your money.

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Originally Posted by Megahurtz

You have two choices. Put the stock exhaust back on or stop being scared of the police. It's in your head that every police officer in Texas hears you when you drive.

. . . . . .

Sorry if this isn't what you were hoping to hear. If you can't accept the loud, I would recommend putting the stock exhaust back on and selling your Corsa to recoup some of your money.

Sorry, I may have overemphasized the 'police' part, it's almost tongue in cheek. In my mind they only go after 2 things - DWI, and racing. Mostly concerned with the loud sound, that it'll never be something I like even for myself.

Thanks for advice on closing NPP and engine damage. Don't want that.

I'm interested in any thoughts on whether stock-NPP-suitcase-behind-Corsa-XPipe will be okay, or if I risk bad obnoxious NPP transitions or drone.

[Slurpee]

It's my understanding that even the OEM exhaust will open the flaps at WOT regardless of exhaust mode. Your new exhaust is just louder, so it's more obvious.

[SOCAL.M6.ZLE]

I was in a similar boat.... Did ARH + HF Cats, and an AWE Touring axle back and DRONE CITY.... was WAYYYY to loud at partial throttle. So I researched and found some guys that added a magnaflow center X muffler in the tunnel and WOW... night and day difference. I have had several ZL1 owners say this is the best sounding exhaust set up they have ever heard. Food for thought.

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Originally Posted by Slurpee

It's my understanding that even the OEM exhaust will open the flaps at WOT regardless of exhaust mode. Your new exhaust is just louder, so it's more obvious.

Aye, I was generally aware, though as you say - very obvious now exactly where it happens.


I'm guessing the stock exhaust is engineered around making this work very well.

I'm interested in swapping back the exhaust but leaving the Corsa X-Pipe. If anyone has just the Corsa X-Pipe I'd love to hear about it, or any speculation on whether that would be okay. It's easier for me to leave it on, if nothing else, even when changing mufflers.

[WhiteMale]

When I shopped a system I believed that Corsa was the loudest most aggressive on the market, even their NPP, which has a very high pricepoint. It seems to be working as expected by your description.
The only closed NPP valve prohibition I've heard was you don't race it on track in stealth mode due to heat buildup. There's no engine damage.
Thing is you dropped a lot of coin there and you can't do anything but add more money to it at this point. Or go back to NPP and try and sell the Corsa which may be pretty tough.

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Originally Posted by WhiteMale

Or go back to NPP and try and sell the Corsa which may be pretty tough.

I just want to get the car to some good spot, I’ll give the corsa a chance to see if it “grows” on me. Wrt $ it would hardly be the costliest fubar I’ve ever made - even in the last few months if I take it off I’ll fish around for some kid who will enjoy it and take it off my hands locally for some amount far below what I paid for it.

The other wildcard is how much difference that xpipe is making.

[CW3SF]

Mine was too loud after replacing the entire exhaust to get a better tone. The fix was installing two MBRP resonators between the high flow cats and the axleback. It toned it right down without removing the growl. Still screams at WOT.

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Originally Posted by CW3SF

Mine was too loud after replacing the entire exhaust to get a better tone. The fix was installing two MBRP resonators between the high flow cats and the axleback. It toned it right down without removing the growl. Still screams at WOT.

Probably a dumb question - does that mean cutting the front of the X-pipe/at the end that touches the cats? Or replacing them?

[CW3SF]

That depends where your x-pipe is installed. On my car I was able to install the resonators in the tunnel in between my two xpipes.

[WhiteMale]

Ya a resonator in the mid-pipe somewhere might be the best option you have, after the X Pipe like the Chief pointed out.

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BTW - as with anything on this forum, every bit of information committed is search fare for future owners of this special but discontinued car. . . .

The information above is good - especially the magnaflow resonator thing, which I may do if/when I ever have work done under there again. . . . Maybe pay someone to weld up pipes such that I can swap the it back and forth with the Corsa X.

My OP may have been based on the original shock from the change, and the greatly exacerbated 'jekll-hyde' nature of the valves opening and closing (the stock engineering of the car almost concealed it).

"What kind of brash belligerent antisocial di**head would drive around in this". With a bit of time, I'm making peace with that, and I'm actually starting to enjoy this exhaust. . . .