[rolijen]

Hey there. My '21 2SS came equipped with the dual output (non-NPP) exhaust. The previous owner deleted the muffler and was running a MagnFlow, axle-back system with no muffler. It sounded amazing but was obnoxiously loud for my neighborhood.

I, being a nerd, decided to DIY an NPP system to tame the sound level in my neighborhood, but open it up everywhere else. About a month ago, I found the correct quad-output muffler with exhaust control valves and actuators on fb marketplace. Then began the fun part--building a controller circuit to open and close the valves (my wife has been calling it my 'science project'). I'm happy to report that I got the circuit board completed yesterday and made the cables to connect to the actuators this morning and started testing the system.

Testing proved the system and it works perfectly with both a wired switch and a wireless remote. I'm now ready to plan the permanent installation in the trunk, under the floor panel, next to the fuse block.

Here's where I need your help: Please share any photos you have showing the actuator wires path on the factory NPP systems. I need to get the cables from the actuators, into the lower trunk space. I assume there are plugged holes somewhere for this purpose.

Please, share photos/videos that can point me in the right direction. I really don't want to drill holes if I don't absolutely have to.

Thank you!

[rolijen]

UPDATE:
I found the NPP wiring ports behind the fiber liners on the sides of the trunk. There is a port with a rubber plug on each side of the body directly above the exhaust valve actuator. I pulled out the plugs and replaced them with grommets and pulled my pigtails up through the holes then slid currogated tubing over the pigtails and pushed the tubing all the way back to the actuators. Everything is taped, waterproofed and zip tied to create a nice path to the controller which I mounted directly in front of the amplifier (left side of trunk floor). Need to get a fuse tap tomorrow (it’s midnight here) and button everything up and test the installed system.

Fingers crossed!

[Ray3768]

That's awesome! Please post a video showing this system in action. I'd also like to see details and pic of the inside of the controller, assuming this is not some sort of top secret intellectual property. I see what appears to be a USB port on the controller. What is that for?


-Ray

[rolijen]

Originally Posted by Ray3768

That's awesome! Please post a video showing this system in action. I'd also like to see details and pic of the inside of the controller, assuming this is not some sort of top secret intellectual property. I see what appears to be a USB port on the controller. What is that for?


-Ray

The usb port you see is an Arduino UNO board. I’m not the first to attempt this, but info on how NPP actually works is very sparse. Basically, the actuator motors run on 12v but require a specific PWM signal to trigger them to move. I found Arduino code and a prototype circuit board diagram online at a Corvette forum and the Chevy SS forum. I’ll add pics later today. And I’ll add links to the code if you want it.

[rolijen]

Ok, I added pictures of the completed install. Happy to say that it works perfectly. Click the remote-->valves open, click again-->valves close. The system remembers the last state so if you close them before turning off the car, next startup, the valves will be closed.

Obviously, this DIY system is On or Off only and is not controlled by the car's computers at all. My goal was quieter starts and quiet driving out of my neighborhood. Once I'm out on the streets, the valves will open and stay that way! Back in the neighborhood, I click the remote and it's quiet again while I park.

In the photos, I'm trying to show the power tap from the fuse box and the wiring to the controller unit which I mounted in front of the audio system amp. You can see the actuator wires at the top of the controller unit (black, yellow, and red wires).

[rolijen]

Here's a short video showing the valves working:

https://youtu.be/TDCfdUq02H0

[Ray3768]

Originally Posted by rolijen

The usb port you see is an Arduino UNO board. I’m not the first to attempt this, but info on how NPP actually works is very sparse. Basically, the actuator motors run on 12v but require a specific PWM signal to trigger them to move. I found Arduino code and a prototype circuit board diagram online at a Corvette forum and the Chevy SS forum. I’ll add pics later today. And I’ll add links to the code if you want it.

Thank you for all the info. Using an open source micro controller makes a lot of sense and you can't beat the price. I'm a huge fan of open source as I type this to you in Firefox running on Linux Mint :-). While my car has NPP from the factory, I am always amazed by people that harness tech to bend reality to their will. I would certainly like to have a look at that code. Gonna have to purchase one of these boards to play with as this has been on my bucket list for some time.

I do have some thoughts about your design that may be helpful for the longevity of the components. I noticed that the Arduino Uno Rev3 spec sheet lacks any environment specifications. Automotive electronics must have increased tolerances to vibration, temperature, and condensing humidity exposure. Depending on the board's cooling requirements, you may be able to encase it in epoxy which would protect it from vibration and moisture. I see that the ATmega328P chip is socketed and not soldered to the board. Simply mounting it on a vibration isolating pad may be sufficient to address vibration. Installing it in a larger enclosure with an intake grille on one side and a small, say 25x25 mm, exhaust fan on the other side can keep humidity concerns in check. The board's thermal dissipation while in use would also be helpful to know. This may be enough heat to dry out the air flowing through the proposed ventilation system, but we would have to calc that to see. Of course humidity could still be an issue when the board is powered off, which is why I would explore the epoxy encasement route.

Then again, we are talking about a part that costs <$30. If it last's 5 years in an automotive environment do we really care? If you were to commercialize this product then it would certainly be an issue, but then you'd also be designing an application specific circuit board that would be less complex with less points of failure.

Anyway, that's all the incoherent rambling I got in me for now. Nice work! Keep tinkering! And thank you for your contributions to the advancement of our wonderful car hobby.

-Ray

[rolijen]

Originally Posted by Ray3768

Thank you for all the info. Using an open source micro controller makes a lot of sense and you can't beat the price. I'm a huge fan of open source as I type this to you in Firefox running on Linux Mint :-). While my car has NPP from the factory, I am always amazed by people that harness tech to bend reality to their will. I would certainly like to have a look at that code….

You are very welcome. Full credit for the solution goes to CityOf9Gates at the Corvette Forum and C4b4the04 at the SS Forum. Their work can be found at the following links.

Corvette Forum: https://www.corvetteforum.com/forums...-retrofit.html

and

SS Forum:https://www.ssforums.com/threads/diy...models.199012/

As far as durability/expected longevity of the system, I built it to be functional but it probably won’t be on the car for more than a year or two. I plan to do a full cat-back exhaust at some point in the next couple of years. For now, it’s nice to be able to control the cold start volume using this awesome GM valve system.