Project 21 | 2-in-1 clubstyle performance exhaust


After months of designing, building and prototyping Dr. Jekill & Mr. Hyde presents the 'Twenty-One', a unique 2-in-1 electronically adjustable exhaust for Milwaukee-Eight Softail Models.*

After months of designing, building and prototyping Dr. Jekill & Mr. Hyde presents the 'Twenty-One', a unique 2-in-1 electronically adjustable exhaust for all Milwaukee-Eight Softail Models. The Twenty-One is made for an audience that wants to take riding a Harley to a whole new level of performance and sound. With this in mind Dr. Jekill & Mr. Hyde created an exhaust that meets all the needs of the clubstyle / performance scene,

without abandoning the characteristic features and innovations of a Dr. Jekill & Mr. Hyde exhaust system. Brace yourself for an exhaust that not only performs like a beast, but also sounds like one. The raw and stripped design makes this exhaust must-have on your Milwaukee-Eight Softail.

*Available for Street Bob // Fat Bob // Low Rider // Low Rider S // Breakout / Fat Boy // Heritage // Deluxe // Slim

Configure the Twenty-One

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Check out the 'Twenty-One' 

The Sound

The ‘Twenty-One’ contains a sound that really brings the power of the M8 engine to new heights, in ways you'd never expected. The thrill of driving is enhanced by a brighter feedback from your exhaust, challenging you to demand that little bit extra from your bike. The exhaust has been subjected to extensive sound tests to create this perfect sound experience.

twenty-one exhaust
  • Dr. Jekill mode
  • Dynamic mode
  • Mr. Hyde mode

adjust your sound to the moment three sound modes

Our exhaust systems embody three distinct personalities: the Dr. Jekill mode, the dynamic mode and the Mr. Hyde mode. By a simple push of a button a valve inside the muffler closes, opens or opens halfway, giving your exhaust more power and sound. You can choose per situation whether you want to ride in the Dr. Jekill mode, dynamic mode or Mr. Hyde mode. It’s up to you.

Learn more

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live demo

3 sound modes


When you choose to ride a Twenty-One you get a full exhaust system with a header set and muffler. Where all other Dr. Jekill & Mr. Hyde exhausts are very clean, we have opted for a rough and unpolished look with this one, including visible welds and discoloring over time. The system is lighter than standard systems, has optimal ground clearance so you can hang comfortably in the bends. But despite the rough and raw look, it matches the quality you are used to from Dr. Jekill & Mr. Hyde.

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What the experts say



For the clubstyle rider performance is of great importance, so this has been taken into account massively in the development of the Twenty-One exhaust. Within the legally permitted standards of course, the Twenty-One significantly increases the performance of your bike. Thanks to the design of the exhaust, there is no loss in performance while riding with a closed valve. This ensures a safe and smooth riding experience, regardless of the mode you ride in.


The Twenty-One is customizable. For the muffler and header set you can choose between a black and brushed edition, with a slashcut or streetfighter end cap in black, alu or bronze. The header sets can be equipped with a full cover of shields or a minimal cover. Visit our exhaust configurator to see what design fits you best.

Configure the Twenty-One

Jekillized 'Project 21' Custom
Low Rider S 

To give our exhaust the attention it deserves we decided to give our own Harley-Davidson Softail Low Rider S a make-over and make it into a proper clubstyle bike!

We teamed up with Chopper Kulture. Owner Mario Kyprianides is well known for his custom bikes and recently won many prices with his unique Harley-Davidson FXR. With lots of custom parts of our trusted partners we are proud to present you an awesome bike that will make heads turn.

Project 21 custom bike

Soon to be revealed


Harley-Davidson is a brand where tradition is one of the main pillars. Even those who don't ride themselves know the chopper ‘easy-riding’ down the American Highway. This is an image that has been moulded into our consciousness and hardly gets challenged. However, like it is the case with every tradition, there will be people questioning its validity and start to see things differently

Originated in the motorcycle club culture, among bikers that needed to ride long distances, a movement grew to customize Harleys on their performance rather than their looks. Everything you changed on your bike was aimed towards making the bike faster, easier to handle and to rip through corners knees to the ground. Started with the FXR, optimized with the Dyna and getting implemented in the new Softails, 

Clubstyle is something not to be ignored in today's Harley scene and for Dr. Jekill & Mr. Hyde it was only natural to build an exhaust designed especially for this movement. Together with renown partners from the clubstyle & performance scene we started Project 21: making the ultimate electronically adjustable clubstyle/performance 2-in-1 exhaust!