Big Twin Torque in a Sport Bike Package?

V-twin Sportbike

Sportbike / June 24, 2017

The 1190RX has a 72-degree, liquid-cooled V-twin engine with a 106.0 x 67.5mm bore and stroke (1191cc), making a claimed 185 peak hp at 10, 600 rpm. Peak torque, which on hi-po bike engines is often just 1500 revs below peak power, is way down at 8200 rpm and is 101.6 lb.-ft. That wide region of strong torque equals acceleration and rideability.

Normally, engines optimized for peak power (for the people who ride specifications) lack the mid-rpm intake velocity to stir the charge for a quick, efficient burn. Usual result? Lack of oomph. EBR worked hard on the RX’s midrange, combining a swirl port that flows strongest at low throttle with staggered opening of the intake valves to achieve old-time rotary charge swirl that speeds up midrange combustion, giving the added benefit of very low unburned hydrocarbon emissions.

The engineers with whom I spoke, John Fox (director of engineering technology) and Dane Hoechst (program manager), are proud of their work. The ideas behind the internal-combustion engine are there for anyone who studies and understands them. You don’t have to be Italian, Japanese, or German to “get it.”

Consider the RX’s high 13.4:1 compression ratio. The danger with high compression in such a big cylinder is that combustion may not be able to outrun the chemical processes leading to detonation. In this RX, fast combustion clearly wins the race, making it practical to gain gobs of torque from such high compression. If you run the numbers at peak torque, RX makes combustion pressure that many a pure racing engine would dearly love to have.

By putting the fuel in the chassis (a combination of welded castings and pressings), the arm wrestle between airbox volume (engines with big cylinders need lots of it) and fuel tank is eliminated. The large airbox contains two giant throttle bodies, each with one port injector and one showerhead.

Buell aims for the shortest achievable wheelbase (55.5 in.), one key to quick steering. The others? Steep rake angle of 22.4 degrees and trail of 3.8 inches. The 17-inch wheels (widths are 3.5/6.0 in.) are uniquely well-braced for the stresses they carry and continue Buell’s focus on low unsprung weight.

That theme is continued in his unique single 386mm front disc brake, which was once characterized by former Buell engineer Abraham Askenazi as “an excellent brake for a street motorcycle.” By attaching to the rim, this disc eliminates the extra unsprung weight of disc carriers.

The two pipes on the right have also drawn comment. The main muffler is, as before, under the engine. The lower up-pipe is a quarter-wave resonator—a muffler element. The other carries exhaust outflow.