Suzuki DF140 Outboard

Trailer Boats used Wellcraft's 180 Sportsman as a test bed for the four-stroke Suzuki 140 outboard engine.

The recent arrival of V-6 four-stroke outboards in the 200-plus hp range has created a sizeable gap. Between 130 and 200 hp, there simply has been no four-stroke outboard. Until now.

Suzuki is bridging the gap — at least partially — with its new 140 hp four-stroke, the first four-stroke outboard in this horsepower category. When Suzuki enters a market segment, it has a penchant for doing so with a technically impressive product. While there is no other brand now competing in this bracket, the new 140 continues Suzuki's tradition of technical superiority. Let's take a closer look.

The Suzuki 140 fills a demand for midrange four-stroke outboard power.

The new 140 — designated DF140 by Suzuki — is essentially a pumped up version of the 90/115 four-stroke I-4 that was introduced last year. This begs the question: How did Suzuki pull another 25 horsepower from the same block?

In principle, to increase horsepower, it is necessary to get more fuel and air through an engine. There are several ways to do this, and Suzuki employed most of them. The easiest way to increase horsepower is to add displacement, and the major difference between the 115 and the 140 is a bore that grew from 3.3 inches to 3.4 inches. This boosted displacement from 119 to 125 cubic inches. The stroke remains the same in both engines, eliminating the need to retool the crankshaft.

Another way to get more fuel and air into an engine is to turn it faster. Accordingly, the wide-open-throttle (WOT) operating range has been increased from 5000 to 6000 rpm for the 115, to 5600 to 6200 rpm for the 140. You may notice that the rpm band is narrower for the 140 (600 rpm) than it is for the 115 (1000 rpm). This is due to an aggressive cam profile on the 140 that provides more valve lift and longer duration.

Stay Cool

An offset drive shaft shits the 140's center of gravity forward for better balance on the transom.

Finally, horsepower can be increased if the intake air can be kept cool and thus denser. This is not always easy, since intake air often passes over a hot engine block en route to the combustion chamber. To help keep the engine block temperature as low as possible, Suzuki has added a water-cooled oil reservoir. Company engineers have also redesigned the cowl to route cool, outside air from the rear of the cowl directly to the intake manifold and expel hot air from the block through vents in the side of the cowl.

Besides adding horsepower, Suzuki has also reduced the weight of the 140. A redesigned clamp bracket and trim system shaved off a few pounds, helping the 410-pound DF140 long-shaft (20-inch-shaft) weigh in at 6 pounds less than the 90/115.

Aggressive cam profiles on the dual-overhead valvetrain give the 140 a reliatively high rpm range.

In addition to the 20-inch-shaft engine we tested, the new DF140 is available in a 25-inch-shaft model. The latter is also available in a counter-rotating version for twin-engine applications. The 25-inch-shaft model weighs 420 pounds, according to Suzuki.

One of the most unique features of the engine, also shared with the 90/115 hp model, is the offset driveshaft. The crankshaft centerline sits forward of the driveshaft, which is driven through a set of gears. This moves the engine's center of gravity forward for better balance. The gear reduction at the junction of the block and tower housing is 1.24:1.

Keeping It Compact

Long-track intake runners help boost low-end torque.

The cam chain is driven from the driveshaft sprocket. The cams must turn at half the speed of the driveshaft, and with initial gear reduction between the crankshaft and the driveshaft, the sprockets that drive the cam can be smaller. This results in a more compact package that will fit outboard splashwells designed for any two-stroke in this horsepower range. Additional gear reduction in the lower unit provides a 2.38:1 overall ratio at the propeller.
Also borrowed from the 90/115 are a water-cooled, long-track intake manifold; cooling fins in the flywheel for the alternator and magneto; 40 amp alternator; hydraulic cam chain tensioner; and sequential multi-port-fuel injection. The multi-function tachometer now includes an oil-change reminder system.

We tested the Suzuki 140 in the waters adjacent to Florida's Key Largo on a Wellcraft 180 Sportsman (see "Related Items" at right). In use, the engine delivers strong acceleration, quiet operation and exceptional fuel economy. It is also runs super clean, complying with California's stringent three-star, 2008 standards for outboard engine emissions, as well as the federal Environmental Protection Agency's 2006 outboard emissions standards.

Suzuki DF140 Specifications and Test Results

Horsepower	140
Number of Cylinders	I-4
Displacement	2.0 liters/125 cid
Shaft Length	20"
Weight	410 pounds
WOT RPM Range	5600-6200
Gear Ratio	2.38:1
Propeller	14" x 20" stainless steel three-blade
Price	$10311

Test Results

Engine	Speed	Fuel	Range(a)
(rpm)	(mph)	(gph)/(mpg)	(miles)
1000	4.4	0.3/14.7	648
1500	5.8	0.9/6.4	282
2000	6.8	1.4/4.9	216
2500	10.0	2.4/4.2	185
3000	11.4	3.2/3.6	158
3500	18.0	4.1/4.4	194
4000(b)	25.6	5.3/4.8	211
4500	27.6	5.9/4.7	207
5000	33.7	7.4/4.6	202
5500	35.1	9.1/3.9	171
6000	39.8	11.2/3.6	158
6200 (WOT)	41.7	11.8/3.5	154