Now the Milwaukee Motor Company upgrades their engine … but only to “8.” That’s the new Harley-Davidson V-twin, and the “eight” refers to the number of valves. Divide 8 by 2 (two cylinders, you know) and you get a four-valve per cylinder design. Plenty of bikes (and cars) have doubled up on the intake and exhaust valves. It helps the engine breath easier without the extra mass of big valves. (There’s that Newton thing about inertia and mass.)
This is a brand new engine from stem to stern and HD is very proud of it. Interestingly, while doubling the valves, they returned to one camshaft to open those poppets. That’s after the last upgrade was proudly showing off its “Twin Cams.” It just shows there are more than one way to skin the old apple. (ASPCA disallows allegorical references to felines.)
While reducing the camshaft count in half, Harley has doubled the spark plug number. There are good reasons for all these changes, as I’ll discuss in the details below.
But first, let’s go to the history books and examine just how often these Milwaukee engineers have practiced engine-eering. I think a definite trend will appear.
This is the ninth big V-Twin engine in Harley’s lineup since 1903:
- 1914-1929 F-Head (61ci and 74ci)
- 1930-1948 Flathead (74ci and 79ci)
- 1936-1947 Knucklehead (61ci and 74ci)
- 1948-1965 Panhead (61ci and 74ci)
- 1957-1985 Ironhead (54ci and 61ci)
- 1966-1984 Shovelhead (74ci and 80ci)
- 1984-1999 Evolution (80ci)
- 1999-2016 Twin Cam (88ci, 95ci, 96ci, 103ci, 110ci)
- 2017 Milwaukee-Eight (107ci and 114ci)
Besides a steady, albeit rather glacial pace of upgrading, you also notice a pattern They just keep getting bigger. Ignore the Ironhead. That went in the smaller Harley Sportster, and so it doesn’t really show the cubic inch progress. Also missing from this list is the engine Harley codeveloped with Porsche, the 2002 “Revolution.” It is water-cooled, and not put in the standard bikes, so I’ve ignored it, although surely Harley engine designers learned from it as well as these listed versions.
The design of Harley’s Big Twins has tracked the development of America’s highways. When most roads were dirt and average speeds low, the Knuck’s iron heads and cylinders handled the heat and “wore like iron.” As roads were paved and four-lane highways began to appear, riders could ride farther, faster. More power being used required increased cooling, so higher-heat-conductivity aluminum replaced iron, first in heads and then in cylinders. Design evolution of the last generation of Twin Cam was anchored by improved cooling.
So what about this new power plant? What does HD say about it? Where will we see it?
The new eight-valve engine seeks two broad goals. One is to make greater power and torque while being emissions-compliant, fuel-efficient, and highly reliable. The other is a trend visible across the vehicle industry — to achieve world-class “ride feeling” through chassis, suspension, and driveline refinement. Customer research, covering 1,000 riders in seven cities, was distilled into “The Voice of the Customer,” telling The Motor Company that riders want more power for two-up riding and more back-road agility. They want the bike to fit more sizes of people. They want cooler operation.
The standard 107 uses precision oil-cooled cylinder heads and will be found in Street Glides, Road Glides, the Electra Glide Ultra Classic, and Freewheeler trikes. A Twin-Cooled version with liquid-cooled cylinder heads and radiators will power Ultra Limited models, the Road Glide Ultra, and Tri Glide models. CVO Limited and Street Glide models are equipped with the Twin-Cooled Milwaukee-Eight 114 featuring liquid-cooled cylinder heads and radiators.
Harley-Davidson Big Twin owners love the look of an air-cooled engine’s fins but have accepted “strategic cooling” (intensive cooling of specific areas) as the price of keeping that look while improving function. In the recent Rushmore series of changes to the Twin Cam engine, this took the form of circulating liquid coolant in passages around each cylinder head’s hot exhaust valve seat and then to external radiators, as a means of keeping valves and valve seats well-sealed and warp-free as more power (and therefore increased heat) was sought.
This is only one of two basic approaches to heat management — removing excess heat to keep parts at safe temperatures. An alternative approach is to change the design so it takes up less heat from combustion — an approach that may also increase power and efficiency by keeping that heat where it works for you — in the hot, high-pressure combustion gas that presses the pistons down to drive the crankshaft.
Therefore the new eight-valve engine abandons the large surface area of the traditional deep, modified hemi two-valve combustion chamber and puts in its place an almost flat chamber of minimum surface area with four valves. A true hemi chamber has exactly twice the surface area of a flat chamber, and to achieve the higher compression ratios needed to make strong torque, a piston in a hemi chamber may need a dome that increases its surface area as well. Thus, by switching from modified hemi two-valve to nearly flat four-valve, the surface area through which heat can enter heads and pistons has been substantially reduced.
Another way to take up less heat from combustion is to speed it up, exposing heads and pistons to flame for shorter time. Faster combustion from two spark plugs per cylinder is one element used in the Milwaukee-Eight to achieve this, but a second is invisible: thousands of hours of flow and combustion simulation studies. Like all modern manufacturers, Harley has relied heavily on powerful computer models allowing engineers to explore options at the press of key. Further use of computers on the bike's themselves produce sophisticated timing and anti-detonation detection. That saves heat and engine parts.
Like the original Big Twin — the EL of 1936 — the new engines have a single four-lobe camshaft in place of the Twin Cam’s pair. Drive is by chain with automatic hydraulic tensioner. Fewer parts mean reduced noise and lower friction. Other improvements in the air intake system also reduce noise. There is a single, outstanding reason for this. Besides monitoring exhaust gas emissions, the EPA monitors noise and the rules keep getting tighter. With motorcycles, the regulations measure the noise in a cumulative, “drive by” manner. That means the noise limits include engine mechanical noise, air noise from engine and body, and exhaust noise. Ah, but one man’s noise is another man’s music. And Harley riders like the rump, rump sound most of all. By minimizing mechanical and air intake noises, you can maximize the exhaust noise that is the primary selling point of the big Milwaukee Iron.
At some point in the future, government regulations may force HD to water cool their engines, since the water jacket muffles much of the engine mechanical noises. But Harely riders like the appearance of the big V-Twin power plant — fins and all, and Harley has been very aware of these design limitations. You don’t have to do a scientific survey of your customers to know where the Harley rider sweet spot applies. Keep ‘em loud and keep ‘em clean looking. That’s the marketing report.
All this effort underlines the importance of the work for Harley-Davidson. The Big Twins, where this new Milwaukee-Eight will be installed, is the very core of Harley’s business, the “engine” that ultimately drives sales all the way down to the last key fob. It’s the heart, soul, and sound that connects to the brand’s millions of fans around the world. Part of the strategy explored by HD includes smaller bikes as "entry-level" sales and the slightly smaller Sportster, yet the money makers are the big boys. In fact, the smaller bikes are part of a plan leading to the top of the line models. Plus you've got to keep the current riders, although they are some of the most brand loyal customers in the business. But they are also mostly an aging population that needs to be replaced with "young blood."
I’m not really a “Harley guy,” but I know a few and I’m very experienced with what these guys (and gals) want. I think the nail has been hit right on the sweet spot, and this engine and the other changes to suspension and various tweaks to the overall bike design will be met with approval by their intended audience and might even add a few more to the crowd. That’s important because the Motor Company has some stiff competition from Victory and Indian, as well as the big twins coming from that small island in the Pacific. The competition is tougher than it has ever been and HD’s bottom line has shown the impact of that competition. This new power plant is bound to help in that area. Just how much it will help is something yours truly will keep an eye on. This does seem like a good direction. The new Milwaukee-Eight combines tradition with the latest engineering and should hit the intended target right on the bulls eye. Time, and sales figures, will prove this assumption.