will adding the npp exhaust from the build site cause droning when driving on the road in tour,sport,and track modes at any time would like to know if it does cause droning?

 

No. This is a nicely tuned exhaust. I have never gotten a drone in any mode.

 

Hmm. The exhaust, when engine sound is set to Sport or Track (where its going to be open at idle and most driving scenarios) is going to be louder then the non-NPP system. And with my HTC with the top down I can definitely hear the louder exhaust with those settings even when doing steady cruising. And sometimes I set it back to Tour where it is closed most of the time except for aggressive driving. And that's the point....you don't have to put it on the louder setting when that is not what you want.

Whether or not that louder sound when cruising constitutes "drone" - I do not know. But when you don't want to hear it, just return the engine sound to Tour, where it only opens for aggressive driving. Or, you can set engine sound to Stealth and then it will never open - but there is really not much reason to do that.

Now, while you can customize the engine sound setting in both MyMode and Z-mode - the engine sound setting is defaulted in the other drive modes as follow (Drive Mode...Engine Sound Mode):
Tour...Tour
Weather...Stealth
Sport....Sport
Track...Track
MyMode...customizable
ZMode...customizable

 

I just finished a 500 mile round trip in my new 2025 C8 Z51 this past weekend, I did the entire trip in "Tour mode" mode one way and "Sport" mode on the return trip with Targa top in place due to questionable weather.
Yes in Sport mode the exhaust note is slightly louder in the cabin but there is absolutely NO drone at either setting when driving at highway speeds.
My only complaint is a pesky rattle coming from the left front side of the Targa top , I know I can easily drown it out with the radio but as soon as I lower the volume I hear it and its very annoying.
There are a few fixes floating round this forum from using silicone on the gadgets, adding O-rings to the front pins and adjusting the rear latch on the Targa top, I am hoping a mix of all three will silence the rattle.
If I am missing another suggestion besides taking the car back to the dealer which I will if none of the suggested fixes work, I am open to additional recommendations.

 

sorry to hear about your problem with the targa top.i don't think i could live with a rattle all the time it would drive me nuts anyway thank you for your exhaust answer.

 

does the stock exhaust have any droning when driving in tour,sport,and track or in v4 mode?

 

Not that I've ever noticed

 

The whole problem with droning that I had with my c6 and some with my c7 is completely eliminated in the C8. It seems the rear engine config did the trick.

 

NO drone with NPP exhaust. Even in Track mode, it is not very aggressive.

 

No Drone.

 

I have an NPP exhaust in a 2022 HTC and it is ideal for me. Top up or top down; and in any mode, it sounds amazing -- with no drone whatsoever.

The NPP exhaust offers the right amount of growl with an elevated exhaust note, and the ability to turn it off when desired. Chevy really did a nice job with this.

 

I have 11,000 miles on My 2023 Z-51 coupe and I have yet to hear any "droning" in any of the modes.
Personally, I am more than happy with the Z-51 exhaust system, it sounds perfect and I love the sound I get from it.

 

NPP is a very good OEM exhaust option. There's no drone, but not as aggressive as some would like.
It's the #1 chosen option among all options for the C8 as 87% of C8s are equipped with it. Do you really want your C8 to be among the 13% that don't have it.
And if you ever go to sell your C8 not having it could very well be a deal breaker for many potential buyers. The option is that popular.

 

I've driven over 10,800 miles on my non-Z51, '24 with NPP in all the different modes. Never had a problem with drone. You'll love the 'note' changes.
Definitely get it. Well worth the $$. If you ever sell it, most buyers would want it. Supposedly adds 5 horsepower, too.

IMO, other must haves are a 2LT interior and the battery protection package. The rest is your personal tastes.

 

At steady state cruising, I couldn't even hear my NPP when it was in track mode. Get the NPP, you will have zero regrets.

 

Nope no drone an also sound not as "good" as my C6 with NPP where I installed a defeat switch!

I'll explain:
The C6 NPP was a pretty good sound. Not as good as the Flowmaster mufflers I installed on mt 1st Vette a 1988 OR the Flowmaster on my S-10 Truck, but OK. I installed a simple switch so it's butterflies stayed open all the time. The C6, like the C7 and C8, those even in Track setting are shut off at lower RPMs. One reason is to prevent a drone at highway speeds. In the C6 I installed a switch mounted on the console to stop the NPP Butterflies from every closing. Easy to do on the C6. Cruising at ~65 mph the drone was bad. Had to flip the switch and let them close. Then no drone.

Had NPP on two C7s. It was possible using a Mild to Wild Device (essentially a relay operated switch) that prevented NPP butterflies from closing. Folks who installed said they had some drone at highway speeds if used. I did not install the device and tested the NPP opening rpm. I (supported by those who installed Mild to Wild relay) found in Track Mode NPP butterflies opened at ~1700 rpm at modest throttle. Below they were closed. In Touring Mode that rpm was about 2500 rpm.

Mild To Wild does not operate in a C8. Trying to keep them open all the time (some have tried) trips a CEL and did not make it sound louder. But it appears the rpm's where they open in the C8 may be about the same as the C7.

BUT in a Coupe with windows up, roof on, where I always drive, the exhaust sound with NPP is NOT as good as the C6 or C7. And the C7s were not as good as the C6. Neither are as good as my 1st Vette or S-10 truck with Flowmaster mufflers.
Tadge had discussed the reasons:

• One being the sound proofing the did on the ME from cabin to engine. They used a glass between 3 times thicker than the widshield, for example.
• He also noted the short coupling from exhaust to CATs to muffler is a reason (yep even with headers.)

BOTTM LINE
That is why many folks have gone to aftermarket exhausts. GM even offers a dealer installed Borla option. Although it is the quietest of 3 that Borla has for the C8. As the C8, from outside the car NPP and Bola sound better. Borla great, NPP OK. But from inside the car in a coupe windows up NPP is marginal! Frankly I would install the loudest of the 3 Borla offers IF I thought it would be significantly better from inside the cabin.

C8's Noisy!
However as quiet as my 2020 C8 Z51 was compared to my 2017 Grand Sport and my E-Ray even somewhat quieter there is still a lot of tire and road noise. You can search for all the folks trying to add sound deadening etc. At best (with systems like sold by Crazy Cowboy two layer insulation) it's still noisy. So I drive 98% with the sound system playing songs from over 1500 I have on a thumb drive to drown out tire and road noise. Starts when I start the car and seldom off. Mostly driving by myself and never use my iPhone when driving the Vette. Spend all my time maintaining my 65 year record of not having an accident with another car by watching out for those who do and are distracted! Have NPP set to Max in all the drive modes I use. At WOT can hear it.

BTW, nothing I have heard, even open exhaust which is harsh is as good as my street rod built when I retired in 2000! The 8.2 Liter BB, with long tube headers, 3" stainless Borla pipes and straight thru mufflers, at WOT the sucking sound thru the 14"x5" Cotton K&N is as loud as the exhaust. When cruising it's pretty tame.

 

No drone, in fact when cruising you won't hear much of anything except tire noise as it will kick into V4 mode and be as quiet as a Lexus.