Making the Harley-Davidson Milwaukee-Eight Engine Scream

The skies had cleared from the day before, leaving the Great Lakes Dragway in perfect condition for our tests. We thundered in on brand new Harley-Davidson touring models equipped with the Milwaukee Eight engine and the three levels of Screamin' Eagle performance upgrades. Having spent some time on the new engine, we were already thoroughly impressed with the improved powerplant (read about it HERE in Marc Cook's review), but now it was time to test out the performance kits. We were there to burn tire, redline, and go as fast as we possibly could. We were there to experience—in stages—how much power the M8 can make. We were not disappointed.

There were only four of us journalists out there testing the bikes, and we were in heaven. The touring models were lined up at the entrance dragway, so that once you were done firing one bike down the line you could hop right onto the next bike. I don’t know how many times I launched, but I was smiling ear to ear every time. Where I thought the changes from stage to stage might be subtle, I could not only see the difference in speed on the clock at the end of each run, but I feel and hear the difference as well.

Stage I is the most popular, the most affordable, and gets installed on a large number of new bikes before they leave the showroom floor. The basic idea behind stage one is to throw more air and more fuel at the cylinders. You bump your intake up from stock to either the Heavy Breather, Ventilator, or High Flow Air Cleaner, each of which has its own trim options, ranging from $175 to $399. The exhaust system is opened up with 4.5-inch Street Cannon Mufflers, with seven available tip options, with the mufflers starting around $500. All of this is then optimized by the Screamin’ Eagle Pro Street Tuner ($299), which uses a new guided tuning system to walk the user through the Smart Tune process and apply the fueling changes.

Hopping off of a stock bike and onto the Stage I is a very noticeable difference, most notably in sound. Because of the more diverse and customizable nature of this kit, the prices can vary pretty vastly based on the exhaust, intake, and trim options you decide to buy. You get a deeper, throatier exhaust note and quicker throttle response off the line. The Stage II and III Kits build off of Stage I, so moving up the line, the more advanced kits will need to have the upgraded intake, exhaust, and tuner as well for ideal performance.

Stage II is where I started to really shave time off my runs. The Stage II kit is a more involved install, upgrading the camshaft and the pushrods ($390). This is offered in two different setups, designed to fit different riders’ style and better suit exactly what they’re going for. The Horsepower Kit uses a Screamin' Eagle SE8-462 cam and mainly focuses on increasing power in the mid- and upper-rpm range. On the flip side, the Torque Kit uses a Screamin' Eagle SE8-447 cam, designed for enhanced torque in the low- to mid-rpm range. With the Pro Street Tuner and the cam upgrade, the engine doesn’t feel wound up and can comfortably cruise around town at low speeds, but when you whip that throttle—all the power is right there, and it comes on quick. Harley says the Stage II kits can give you an upgrade of up to 14 percent more torque and 24 percent more horsepower. I found that I preferred the Torque Kit to the HP, primarily because of my love for the low-end power Harleys are known so well for.

The first time I lined up on the Stage III Road King, I just spun tire like a fool. The second time, I was too soft on the clutch and had a slow launch, but recovered and pulled a decent time. The third time, I finally got a run I was proud of and really got the see what the M8 can do when it’s all opened up. Stage III ($1,600) is big. Bigger bore, higher-compression pistons, as well as a cam and lifters, providing a claimed 24-percent increase in torque and up to 39 percent more ponies. You get more power that lasts throughout the entire range. The difference between a stock bike and a Stage III for me, was 13.70 to 12.70 seconds on the quarter mile. Not to mention the feel, the sound, and everything else that comes from upgrading all these systems on your bike.

Since I started riding old scooters and enduros in my teens, I have always been told “nothing is as reliable as when it came from the factory.” Now I know that concept has its faults and has been proven wrong many times, but hey, when it comes from the factory that way, you have someone to blame if something goes wrong. One of the highlights of Harley-Davidson’s Screamin’ Eagle program, then, is that H-D is right there to take the blame (or more likely the credit in this circumstance). Your Stage II Cam is still covered under factory warranty. Bumping your CVO from a 114ci to a 117ci won’t harm that Original Equipment Factory Warranty that is so valuable when you buy a new bike.

Harley-Davidson has moved forward in massive strides with the new bikes. You get stronger, smoother power throughout the entire range of rpm, and better handling with the improved suspension. The Screamin’ Eagle Kits build on that platform to give you a dramatic increases in power, while maintaining rideability, comfort, and that sacred factory warranty.

For more information on the Screamin' Eagle Kits, check out Harley-Davidson.com. And to see some of that sweet gear I'm wearing, check out RolandSandsDesign.com.