Kracka

Mode should not matter when performing the relearn procedures as the full sweep is utilized. With that said, I never have a car in Z-Mode when performing the procedures (I use Tour).

Hockeyfun1

I'll try driving it in a few hours or in the morning when it cools off. What would you suggest at this point? I'm not sure why I get a cold loud rattle that goes away when it warms up.

Kracka

I hate to say it, but probably a defective valve...

Could it possibly be a loose heatshield, though?!

Hockeyfun1

I'm thinking it might not be anything loose since it goes away when the engine heats up.

My first one had a defective valve and made rattling. This is much louder but shorter in duration.

Kracka

Heat will alter a heatshield rattle. My decades with turbo imports taught me that!

Hockeyfun1

It's 50F outside so not in the 30s like the other day when I got the loud noise upon starting to drive. You can still hear a slight rattle in this video. Any idea about it?

Also in this second video, I was coming to a stop and doing a u turn and accidently downshifted to 1st gear with the paddle shifter. My car was still in D mode, not M mode (never was) and it didn't want to shift up. I had to do it myself with the paddle shifter to get it in second gear. Unrelated to the Borla but any ideas? The exhaust made a weird noise.

ArizonaZ06

With the hell you've goon through with the Atak I would get Borla to refund you.

There's plenty of performance with the NPP. After all this get your Borla money back and put on a set of HJS 200 Cell Cats that will give you a deep idle sound and a serious growl to or before redline. The HJS flow is 92% of a straight pipe with not one CEL.

OR, just a thought. Pretty sure Kracka has quality Corsa's Cats that are half the price of HJS, with your Borla refund $$, add on headers that are both together less than the Atak. Headers and Cats together is an easy install. I have both with my NPP.

https://soulpp.com/product/chevrolet...ic-converters/

Kracka

Correct, aFe headers + Corsa cats here. Zero CEL's 2+ years and counting.

Kracka

Nothing else is possibly loose from the install? If not, then I'd say it points to a faulty valve in the Borla system somewhere.

Unrelated to the exhaust, this is normal behavior. By hitting a paddle, you temporarily entered manual mode.

Hockeyfun1

Since I have NPP, in an exhaust on my car, I want the ability to change the noise to be lower or louder. If I take the car out of Z mode with the ATAK, the sound is reasonable. So that's why I wouldn't want to change the cats. Plus NY has new laws about that with passing inspection. If you were me, would you try Corsa exhaust or just go back to stock?
​​​​​​

Kracka

If I were you, I'd let Borla take care of you under their warranty. Let them replace the system and cover your labor to do so.

Hockeyfun1

They already did that once and were making it seem like it's not really compatible with my car.

Vetteman Jack

If Borla does not think the exhaust system you have is not compatible with your car, take them up on their offer of refunding your costs. The NPP system from GM is not a bad one at all.

Kracka

Oh that's right, you mentioned that. In that case, absolutely full refund and go with Corsa.

Hockeyfun1

What Corsa is equivalent to the Borla ATAK? Any suggestions on where to get it from?

Kracka

You'll want the 4-valve system with mufflers, your choice of exhaust tips (polished, black, or carbon fiber).
SKU: 21100
https://www.corsaperformance.com/pro...tory-npp-21100

@Corvetteexhaustsystems is your man for anything Corsa. His customer service was incredible when I bought my cats. He's in NY as I see you are too.

Corvetteexhaustsystems

Yesssirr I do have Corsa options in stock & ready to ship if you want to try something new. If you're not too far away maybe I can have a look at your car to see if there could be any issues with your setup currently.

MarkMeHopeful

Not doubting you at all, but did they say why they it's not really compatible with your car? If you originally had a NPP exhaust, aren't all C8's created equal?

SnowyATX

^^
Sounds, pun intended, like they are giving up. Complete cop out to say not compatible. That being said I’d be frustrated as hell. What are the odds two systems are doing it unless you received two of a “same bad batch of valves”. I’d love a better exhaust on my ‘24 Z51 but the wife would kill me considering how new it is. Also a little leary about about warranty once I get out into the GMEPP timeframe.

Good luck, has to be a royal pain.

Kracka

If warranty is a major concern, then I'd suggest GM's optional Borla system installed by your dealer. Tough to argue it being fully validated by GM engineers and warranty-compliant if installed by the dealership. You can order it directly from your dealership or the Chevy Accessories website.

https://accessories.chevrolet.com/pr...iGAhmuv3E%253D

$4,243.40 right now with the current ROAD20 promotion code (plus tax & installation).