I've spent the last year or so developing a project to build a true drone free exhaust for my 2016 GSF.

Drone is something I find incredibly annoying and as a result I had to return the Borla "drone free" axle back I got because it certainly did have drone in my opinion. I've come to realize everyones tolerance for drone is different and one person could think its drone free but another doesn't. Also realized that essentially any aftermarket exhaust will have some drone. I really want to wake the car up but I can't stand drone.

I liked the idea of a valved exhaust but anything on the market is still too loud when valves are closed in my opinion. My ideal setup would be a valved stock exhaust however you still get drone with the valves open. That's why I decided to pursue a project that I'm not sure has been done as far as I could find. There are OEM systems like this but to my knowledge they aren't used to tune out drone. I wanted to build my own active exhaust system that can be tuned to automatically change the valve position depending on how I'm driving but more importantly automatically close the valves off in the droney regions of the RPM/throttle map.

I wanted a super reliable system so I opted to go with a OEM Roush exhaust valves. All the OEM valves require proprietary signals from the engine computer to operate them, so without the knowledge on how to reverse engineer the software I opted to install my own motors on the valves that I could easily control with an Arduino style microcontroller. I fabricated some custom hardware to adapt my motor to the Roush valves. I used a high torque servo made for RC car steering systems and its plenty powerful and fast.

This is the valves how I bought them



And after adding the servos





This is the microcontroller I'm using to interface with the car and collect the RPM and throttle data. I can also use it to command the valves open and closed. So far I've been able to get it to command the valves open and closed when RPM and throttle position reach certain thresholds. This gives me full ability to tune the valve behavior for any conditions. I am programming a mode switch so I can toggle between manual control with a **** or different tunes for automatic mode. I could potentially make different tunes for sport and sport plus mode to enable those automatically.



That's where I'm at on the project, will continue to post updates as I go. My next step is to get the valves installed into the exhaust, I just need to find a shop to do the install.

 

Looks like an awesome project. I'm a big tech nerd as well and love to see yet another awesome use for an arduino !

 

Was on this quest too. Tried the RR valved exhaust and the drone was horrible.

Went to my local shop HotRodScott.

When closed it sounds almost stock. When open it is loud.

 

Finally an update. After a lot of trial and error I ended up on my true drone free exhaust. I ended up going with a Borla axle back with OEM midpipe and put the cutout valve inline with the right side exhaust right next to the muffler.

I also tried putting cutouts from the OEM axle back right behind the muffler and unfortunately it made almost no difference in the sound output. I was very disappointed with how quiet it still was.

After installing the Borla axle back there was some drone though not too bad between 1600 and 2300 RPM at light throttle.

Testing showed me that when closing off one side of the exhaust it completely eliminated the drone. One of my theories is that the tailpipe section of the exhaust system acts as a quarter wave resonator canceling out the drone. My other theory is that its just quieter with only one exit.

Since the midpipe has an "h pipe" which is actually a large merge you can close off either side of the dual exhaust and still get flow for both engine banks through the open side.

I was able to program the Freematics OBD system to read engine RPM, load and throttle %. Using these inputs I can command the exhaust valve to any position based on the inputs. What I ended up doing was programming the valve closed only during the "drone zone" which for me was 1600-2200RPM with throttle between 17-55%. This will make sure that during decell and during hard acceleration the valve will remain open, but if I am cruising around at low throttle the valve will close off in the "drone zone" and eliminate the drone.

The restriction created by running both sides of the exhaust is negligible during low throttle/load conditions and that's why I'm able to close off one side.

At this point this is my perfect exhaust. Sounds great throughout the RPM range without the annoying drone between 1600-2300 RPM.