Like a sundae with a cherry, the Mercury 115 Pro XS is an outboard with a little extra. Sporting XS graphics that match those on the V-6 Pro XS Mercs, this inline-four motor is mechanically identical to the 2.1-liter Mercury 115 FourStroke. Remapping the engine control unit (ECU) moved wide-open throttle from 6,000 to 6,300 rpm. Voila — more performance.
“Horsepower is simply torque times rpm,” declares David Foulkes, Mercury vice president of product development. “As long as the torque curve is still climbing, if we add rpm, we get more power. And the 2.1-liter makes plenty of torque.”
With an extra 300 rpm, boaters can go down one propeller-pitch increment and gain acceleration with no loss of top speed, or they can run the same prop and go faster. Mercury says the 115 Pro XS is about 1 mph faster compared with its 115 FourStroke.
Likewise, the Evinrude 115 HO, Suzuki 115 SS and Yamaha VMax SHO 115 are styled like performance models. At 359 pounds, the Mercury is the lightest of the bunch by 18 pounds, and it offers more displacement than the 2.0-liter Suzuki, the 1.8-liter Yamaha or the 1.7-liter Evinrude. That’s a significant spec — displacement is what gives an engine bottom-end power.
The 115 Pro XS comes in 20- or 25-inch shaft lengths and either the standard 4.2-inch-diameter gear case with a 2.07-to-1 ratio or a 4.9-inch Command Thrust gear case ($330) with a 2.38-to-1 ratio. The Command Thrust case accommodates props up to a 16-inch diameter and produces more lift, which can improve performance, though it also creates more drag, so faster boats may perform better with the 4.2-inch case. These options plus the wide selection of Mercury props make it possible to really dial in performance.
I could feel the lift effect of the Command Thrust case and Enertia prop on our Ranger VS 1780 test boat. This boat was also equipped with the new Mercury Active Trim system, and it worked flawlessly. Most impressive was the quiet operation at idle and cruising speeds. At idle, we could not hear the motor over our conversation, even in this smaller boat.
The Mercury 115 Pro XS has a list price of $10,830, a $220 upcharge from the standard 115 FourStroke.
