The Harley-Davidson M8 Engine


It’s a great day for a ride. As I am about to start up the bike, I got to thinking about this latest V-Twin from Harley-Davidson. How does a company, like Harley keep their tradition alive and continue to develop new performance options?  By balancing nostalgia with new technology.

The ninth generation of the “Big Twin” engines developed by Harley-Davidson is only the third All-New Big Twin in 80 years! First introduced in the 2017 Touring and Trike models, these massive power-plants differ from traditional Harley Big Twins with its four valves per cylinder, giving it the namesake with a total of eight valves. The mill also returned to the single-camshaft design as used on previous Big Twins from 1936-1999 this time with internal counter-balancers to reduce vibration.  The M8 was not the first Harley big twin engine to have 4-valves for cylinder.  The V-Rod engine jointly engineered with Porsche in Germany sported 4-valves and revved to 9,000 rpm with a claimed 165 hp for the 79 cid Screaming Eagle version.  Unfortunately, the 60 degree V-twin in the muscle cruiser was not well received by the Harley crowd. 

The improvements to the touring engines was one of the results of the Rushmore project which started with over 1000 interviews in seven cities across the country. They were asked what they would like to see in a new Touring bike from Harley-Davidson. The survey resulted in three main areas of improvement for the engine: More power, less heat and less vibration. The factory was able to increase the power while also keeping the range and fuel economy similar and, in some cases, making it even better. They were also able to reduce the exhaust temperature by 100° by moving the catalytic converter farther away from the rider and introducing a water cooling solution. The vibration issue was resolved modestly with the internal counter-balancers mentioned earlier. The vibration was reduced by 75% keeping in mind the hardcore base Harley fans. 

Each of the three size configurations of 107, 114, and 117 cubic inches activate their valves with push-rods. The stock CVO models with the 117 pushing 124 lb/ft of torque with rear wheel power at 112.51 lb-ft torque at 3,400 rpm!  But as usual, Harley Davidson gave the aftermarket tuners a fantastic platform to make more power.  The new 4-valve heads can flow a ridiculous amount or air which when combined with fuel makes ridiculous amounts of torque and power.  We have customers making close to 250 hp with naturally aspirated engines measuring over 150 cubic inches.  In fact,  just this week one of our customers is building one with over 186 inches!  Burns Stainless has led the pack in building exhausts that support the new power levels.

The new Big Twin “M8” has resulted in excellent reviews from riders and the motorcycle press. And now in its 5th year, the engine is a welcome enhancement to the racing community as well. Drag racing the big touring bikes has been a sport for many years, but as reported earlier in this blog, road racing with the King of Baggers and Bagger League Racing seres was started only a few years after the launch of the M8. This larger power-plant makes an easy entry into this wild and ridiculously awesome sport.

Milwaukee 8 Custom ExhaustAs mentioned, the aftermarket has jumped on board with the new mill as well. Though the heads can flow mightily, the engine was plagued with weak cranks, poor oiling systems, cracking cylinders and more that were exasperated when the power levels were increased.  There are some great tuners that have reliable parts and kits available to make your fire breathing beast come to life.  Plenty of tuning, big bore kits and the like are available by many carriers. Burns Stainless has taken this into account and offers a high-performance stainless steel exhaust systems for the Milwaukee Eight. With two in-stock systems with reverse cone megaphone mufflers in short or long CVO style applications. We also offer the parts and pieces to go along with our revolutionary X-Design Parametric Exhaust Modeling Program for those who have increased bore/stroke, and engine performance and require an application specific custom exhaust solution. Enter in your engine specs and we will craft a winning combination of stepped tube size and length to get the largest power band available for your specific needs and application.

OK, now it is time to throw a leg over it and head down the coast for a nice torquey ride. Click HERE to hear the roar of the NhB Reverse Cone Megaphone exhaust system for the Milwaukee Eight.


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