Close-Up: Suzuki Boulevard M109R Motorcycle

At less than 1800cc, Suzuki's new Boulevard M109R big twin won't set any records for displacement among the recent entries into the big twin motorcycle class, but the sleek new 109-cubic-incg Boulevard could be the strongest of the big twins. A glance will tell you of its performance intent, but you'll have to look deeper to find out how it makes its more than 120 horsepower.

Sportbike Influence

The R suffix in the biggest Boulevard's designation, that little headlight fairing, and the seat cowl all hint at sportbike thinking, but the engine is where the advanced sportbike technology actually shows up. While the rest of the cruiser world has been rushing to embrace pushrod valve operation, Suzuki uses dual overhead camshafts (DOHC) to operate two each 1.7-inch (42mm) intake and 1.5-inch (38mm) exhaust valves. The valves are set at a narrow 27-degree included angle. The only other engine I can think of that was introduced for cruiser use with a DOHC valve train is the 1130cc mill in Harley's Rod series bikes.

Of course, chains drive the cams, but to keep the camshafts' sprockets small and light Suzuki uses a two-stage drive with an intermediate shaft and sprockets to allow a drive reduction. This permits smaller cam sprockets, which in turn means more compact cases and less weight up there at the top of the engine and dropping the center of mass.

The big 1783cc V-twin is liquid-cooled of course. The radiator has a shroud, most of which is color-matched to the bodywork with a bellypan/skid plate that's unfinished metal. The 54-degree V angle gives the downdraft intake ports a fairly straight shot at the combustion chambers. Like other Boulevards, the M109R uses offset crankpins for perfect primary balance. It's also rubber mounted and has a balancer shaft, making it the only bike I can think of to use all three counter-vibration strategies. You can hear the crankpin offset in the exhaust cadence, so even though it looks like a traditional narrow-angle V-twin, the deep. Solid exhaust note doesn't exactly mimic one.

Chicks Dig Guys with Big Pistons

The pistons are a 4.4 inches (112mm) across, which, according to Suzuki, makes them "the largest reciprocating engine pistons being used in any production passenger car or motorcycle on earth." The fat slugs get short racing-style skirts and cut-away sides in the interest of friction reduction. The top rings have L-shaped sections so that combustion pressures push them out against the cylinder for maximum sealing. Through an exotic process called physical vapor deposition, the oil-control rings get a chrome-nitride plating applied in a vacuum chamber where positively charged chrome-nitride vapor is applied to the negatively charged ring face for an exceptionally hard, smooth surface. The rings run against cylinders coated with SCEM (Suzuki Composite Electrochemical Material), which Suzuki says further improves the ring-cylinder seal and reduces heat and wear.

The engine inhales through two airboxes and a pair of 56mm (2.2-inch) dual-throttle-valve throttle bodies. In the dual-throttle-valve system The ECM (engine control module) monitors the rider controlled valve and responds by opening the second throttle valve to a point that provides intake velocity. This injection system has an idle speed control feature that allows it to warm up smoothly and idle smoothly under varying conditions. The 32-bit ECM also varies spark timing, staggering the timing of each cylinder's two spark plugs under heavy load.

The two-into-one-into-two stainless-steel exhaust system features a catalytic converter as well as a butterfly valve to adjust back pressure to match the engine's mode. Suzuki's acronym is SET (Suzuki Exhaust Timing), and it provides more back pressure to improve torque at low rpm, opening as rpm increase. Suzuki says this helps provide strong low-rpm torque even though the M109R design favors mid-range and high-rpm power.

Suzuki put the clutch on a balancer shaft behind the crankshaft. There are five speeds in the gearbox, and the M109R maintains Suzuki tradition of shaft drive for its big cruisers.

The Frame Up

The Boulevard M109R's chassis reflects a sportbike's influence as well. The high-tensile-steel frame with its cast aluminum swingarm (we expect to see some owners polishing them right away) embraces the new engine, with six rubber mounting points. Up front, inverted 46mm KYB cartridge fork legs bracket a smallish fender and two radial-mount Tokico calipers from the GSX-R1000 pinch 12.2-inch discs. Both wheels are 18-inchers with radial Dunlop D221 tires. The 8.5-inch rear wheel and 240mm tire (the widest of any Suzuki to date) are stopped with a two-piston caliper and 10.8-inch disc.

Suzuki supplied dimension data that conflict somewhat. For example, different sources give rake as 32 or 31.25 degrees, front wheel trail as either 4.4 or 4.7 inches, and fuel tank capacity as either 4.9, 5.0 or 5.1 gallons. However, seat height and wheelbase dimensions are consistent at 27.6 inches and 67.5 inches respectively.

The styling is sleek and aerodynamic. The small headlight cowl leads the way ahead of blade-style handlebar risers. Above the bar there is a bar-style LCD tachometer. Other instruments include an analog speedometer and an LED odometer, dual tripmeter, clock and fuel gauge. You can exchange the seat cowl shown here for a passenger seat (both are supplied with the bike). The taillight is a big LED. The single-shock rear suspension leaves the rear wheel and unencumbered, particularly on the left.

Suzuki has definitely target the performance big-twin segment and its claims are true, it should have no trouble laying claim to that title.

Specifications
2006 Suzuki Boulevard M109R

Suggested base price: $12,399
Standard colors: Black, silver, or blue
Optional colors: None
Engine type: Liquid-cooled 45-degree tandem V-twin
Valve arrangement: DOHC, 2 intake, 2 exhaust valves
Displacement, bore x stroke: 1783cc, 112 x 90.5mm
Compression ratio: 10.5:1
Carburetion: EFI, 58mm throttle bodies
Transmission: 5 speeds
Final drive: Shaft
Seat height: 27.6 in.
Claimed dry weight: 695 lb.
Fuel capacity: 4.9 gal.
Wheelbase: 67.5 in.
Overall length: 96.9 in.
Rake/trail: 31.25o/ 4.4 in.
Wheels: Cast alloy, 18 x 3.5 front, 18 x 8.5 rear
Front tire: 130/70R18 Dunlop D221 tubeless radial
Rear tire: 240/40R18 Dunlop D221 tubeless radial
Front brake: Two, 4-piston calipers, 12.2-in. discs
Rear brake: 2-piston caliper, 10.8-in. disc
Front suspension: Inverted 46mm stanchions, 5.1 in. travel
Rear suspension: One damper, 4.7 in. travel, adjustable for preload