Harley's just-announced program "More Roads to Harley-Davidson" introduces "a new modular 500cc to 1,250cc middleweight platform," including 975 and 1,250 V-twin engines to launch in 2020. These are liquid-cooled, appear to have DOHC, and almost certainly have four valves per cylinder. Their vee angle is close to 60 degrees. Other than this we have no information.

So let’s speculate, based upon established Harley practice but also including the possibility of some deviations from it.

Harley has historically worked with peak-power piston speeds of 3,500 feet per minute. Piston speed is just twice the stroke in feet, multiplied by rpm. Its engines, when bikes are tested on rear wheel dynamometers, tend to produce stroke-averaged net combustion pressures of 120–130 psi at peak power, and 130–140 psi at peak torque. Engineers call these pressures "BMEP," for brake mean effective pressure.

With the exception of the G-bike and the apparently discontinued V-Rod, they have chosen bore-and-stroke ratios of about 0.9 (meaning the bore is roughly 9/10 of the stroke length). Harley-powered Buell sportbikes have shown that it’s possible to run their engines at higher piston speeds (4,320 feet/minute in the case of Ulysses) and somewhat higher BMEPs.

Modular engine design
As a modular engine design, it is likely that 975cc and 1,250cc variants will share the same stroke.Courtesy of Harley-Davidson

Because of that word “modular” in the first paragraph above, I’m going to assume that the 975 and 1,250 engines will share a common stroke. Just pulling some numbers out of the air, let’s give the 1,250 a 96.5mm bore by 85mm stroke, and give the 975 85 by 85mm. That, combined with the longevity-increasing 3,500 feet/minute piston speed, gives us 6,275 rpm at peak power for both engines. Torque figures for Harley engines have typically been in the range of 0.85–0.95 times displacement in cubic inches, very often given at 3,500 rpm.

More poking at my ancient TI-35 II gives me the following:

Horsepower and torque using traditional piston speed and BMEPs:

1,250 (76.3ci) 77 hp @ 6,275 rpm 69 pound-feet torque at 3,500 rpm
975 (59.5ci) 60 hp @ 6,275 rpm 54 pound-feet torque at 3,500 rpm

Okay, now let’s push piston speed up to Buell level—an increase of 23 percent. Understand that this increases bearing loads and vibration:

Horsepower and torque using Buell piston speed and traditional Harley BMEPs:

1,250 94 hp @ 7,718 rpm
975 74 hp @ 7,718 rpm

Hmm, we're still not busting that 100-hp barrier, so let's try again, this time with Buell piston speed and higher BMEP from a Buell-type sportbike engine:

1,250 114 hp @ 7,718 rpm
975 89 hp @ 7,718 rpm

You’ll notice I have not included torque figures for the second and third cases above. The reason is that when you tune for increased power, the rpm of peak torque rises and there can be substantial loss of torque in bottom and even midrange. Let us therefore include numbers for the obvious competition for the 2020 Harley 1250: the Indian Scout.

Indian Scout 1200 85 hp @ 8,620 rpm 64 pound-feet torque @ 4,300 rpm

Scout is giving its peak power up at a 4,163 feet/minute piston speed, not quite in Buell territory but significantly above cruiser territory (far above the 3,382 feet/minute of Indian 111).

Could be some folk still aren’t satisfied, so let’s completely drop the idea that we’re building cruiser engines and go all the way to racing bore-and-stroke ratios near 1.5 and also go for broke in terms of BMEPs. The easy way to do this is to get rear wheel horsepowers for Ducati’s Panigale 1299 and 959 V-twins, which already exist:

Panigale 1299 177 hp @ 10,700 rpm
Panigale 959 136 hp @ 11,040 rpm

Before you run a forefinger down the above list of speculations and pick the one you like best, here’s a cautionary question: Why is the V-Rod, a model whose engine was designed by Porsche to include up-to-date practice in every area, not included in the 2018 model lineup? Having a look around, we find that US dealers didn’t know what to do with V-Rod, and that most Harley customers, while perhaps enjoying V-Rod’s strong performance, decided it wasn’t a “real” Harley. Another factor is that performance cruisers, in general, have always been been slow sellers in North America. However, the V-Rod is said to have done well in foreign markets—notably South America—and is said to have sold more than 100,000 units. It’s clearly a good motorcycle, but in Harley’s market that is not enough.

Here are some rear-wheel numbers for V-Rod:

V-Rod 1250 104 hp @ 8,250 rpm 72 pound-feet torque @ 7,000

Why would a population of riders say V-Rod is not a real Harley? Was it the styling—long and low, influenced by the drag strip, but different from familiar Milwaukee cruisers? Or was it the contrast in engine features—liquid-cooled, plain bearings, four valves, non-pushrod? Or was it engine character? While we know it's possible to get endless flat torque from a four-valve engine, notice that V-Rod's peak torque is up at a number that is twice that of traditional Harley engines. Twice. This is the level these new engine should be at to meet the competition.

Harley-Davidson engine
Power figures of the new Harley-Davidson engines are dependent on bore, stroke, piston speed and BMEP.Courtesy of Harley-Davidson

I can’t afford to run the necessary focus-group series to answer these questions, but I do believe they posed a challenge to the product planners who had to decide what performance to give Harley-Davidson’s 2020 1,250 and 975 engines. Will they be “real” Harley-Davidson powerplants, with traditional performance? Or will they, as V-Rod was, be something completely different?