For several years, the big news in outboard power has been the horsepower race; for instance in 2007 when Suzuki introduced the DF300, the first four-stroke to crack the three-o-o barrier. But this year – given the fluctuating gas prices – the emphasis is on smaller, lighter, more fuel-efficient power. Once again, Suzuki rises to the occasion by giving us the DF70, 80 and 90, three new engines that deliver improved levels of economy and ­performance.

Out With the Old
 Last year, the DF90 was basically a detuned DF115, which weighed 416 pounds and had a displacement of 118.9 cubic inches. The engine’s smaller sibling, the DF70, shared the same platform as the DF60 and displaced 79.2 cubic inches. This year, the DF70, 80 and 90 share a new in-line 4-cylinder block that displaces 91.7 cubic inches and weighs just 341 pounds – the lightest 90 hp four-stroke on the market. This new generation shares some of the features that give the higher horsepower models their blazing power, like dual overhead cams, multipoint sequential electronic fuel injection, a timing chain rather than a belt and two-stage gear reduction that allows them to swing a bigger prop.
 Aside from the decal proclaiming the horsepower, the only differences among the DF70, 80 and 90 are internal, with different engine computer mapping and a different cam profile. The DF70 and DF80 make peak horsepower at 5500 rpm with a max engine speed of 6000 rpm, while the DF90 reaches its potential at 5800 and can spin up to 6300 rpm.      

Lean and Mean
 While the DF70, 80 and 90 share some of the same technology that made the DF300 possible, these engines herald a new generation of outboards for Suzuki. One of the new features is the Lean Burn Control System. Most engines keep the air/fuel mixture ratio constant, but after getting on plane and settling into a constant cruise speed, engineers at Suzuki discovered that you could reduce the amount of fuel in the mix and still have it perform within normal operating parameters. Light aircraft have been doing this for years, so it’s a proven fuel-saving technique.
 During tests this year in Key Largo, Fla., the improvement in fuel economy was confirmed. Using the Carolina Skiff 198 DLV as a test platform for the DF90, mileage was measured at 8.63 mpg at a cruise speed of 21 mph at 3500 rpm. At idle, the in-line four-cylinder powerplant gets an astounding 23 mpg – better than a lot of land-based vehicles. To compare this to the previous DF90, we looked at gallons per hour burned by both at a typical cruising engine speed. At 4000 rpm, the old version burned 4.7 gallons per hour, which is very respectable, but the new model burned just 3.0 gallons per hour. This improved economy is also made possible by reducing friction on moving parts by using a new oil pump that more efficiently delivers lubrication where you need it.

Shrinkage
 This year, a new gearcase with a smaller profile also reduces drag for better economy. Like the DF300, the DF90 uses an offset driveshaft, which not only makes the engine considerably more compact, but also reduces vibration by moving the center of gravity closer to the boat’s transom. In addition, this year’s DF90 is 4 inches shorter than the previous model.

What’s New
‹ An up-tilt limiter keeps your cowling safe if you’re not paying attention.
‹ A down-trim motor sensor automatically shuts the trim motor off when you reach the maximum trim down level.
‹ An Easy Start System allows the driver to turn the key and let go immediately. If you try to restart while the engine is already running – a distinct probability when they are this quiet – nothing happens.

Test Run Results
 Idling out of Key Largo’s upscale Ocean Reef Club Marina on a 19-foot Carolina Skiff 198 DLV with the DF90 on the transom, we measure an ultra-quiet 55 dBa on the decibel meter and saw and felt minimal vibration. Reaching the end of the no-wake zone I jammed the throttle and experienced a burst of acceleration, exactly like you used to not feel with older four-strokes. Lack of low-end punch has been the most frequent complaint over the years about four-strokes, but this new breed seems poised to blow that adage out of the water. We were on plane in 3.3 seconds and accelerated to 30 mph in just 6.7 seconds. We cracked the 40 mph barrier and even at this speed we measured a relatively quiet 92 dBa even though we were very close to the engine.