While larger outboard engines tend to get most of the headlines, 40 percent of registered powerboats in the U.S. are smaller than 16 feet in length and are designed to be powered by more modest engines. Traditionally, such engines have been the last to receive state-of-the-art technology, but not at Suzuki. In fact, this bread-and-butter boating segment now has two of the most advanced engines on the market: the DF25A EFI and DF30A EFI.
Instead of just tweaking previous designs, Suzuki went for a fresh take on what portable power can be with its new 25/30 class. They sport a 0.5L block that’s now an in-line 3-cylinder design instead of the old V-twin configuration, resulting in less vibration and smoother performance. Despite the extra cylinder, they are the lightest 25 and 30 hp engines in their respective class. The DF25A, which is offered in a non-electric start configuration (the 30 isn’t), weighs in at 137 pounds (manual 15-inch shaft model). That’s as much as 31 pounds lighter than its fellow four-stroke competitors and is even 10 pounds lighter than its two-stroke competition’s two-cylinder offering.
So how did Suzuki cut the weight? By using lightweight composite materials instead of metal for items such as the inlet manifold, the fuel injection system, the recoil start system, and several brackets and covers. And they have electronic fuel injection (EFI), which obviously requires electricity, but the manual-start models feature battery-free designs that use a magneto instead to supply the juice.
Slip Slidin’ Away
To reduce friction for better fuel economy and to lessen vibration, the dynamic engine duo features roller rocker arms with internal bearings, which means the rocker arm is rolling over the camshaft lobe rather than scraping over it. An offset crankshaft reduces the pistons’ friction against the cylinder wall for a smoother, more efficient motion.
A new cowl design allows the direct intake system to have a smoother, cooler flow of air thanks to a rotating flywheel that helps vent warm air from the recoil cover, the inner air intake and the outside of the engine cover, reducing temperatures under the hood. The cowl design, together with a newly designed air cleaner, allows much higher power output from its relatively small displacement.
I tested the DF25A on a variety of boats in Key Largo, Fla., including a Qwest 816 pontoon, a fiberglass Carolina Skiff J16 and an aluminum Sea Ark 1548 DKLD, and I was impressed with its quietude and its attitude. Thanks to its EFI fuel delivery system, the power comes on smooth and strong, especially in the mid-range. Time to plane on the Sea Ark was 3.1 seconds, and it reached 20 mph in only 5.5 seconds, with a top speed of 25.7 mph. Having a power trim option on these engines is a huge plus when you’re trying to wring out the most performance for many boats by reducing wetted surface. On the Carolina Skiff J16, we could have used the optional electric trim. The time to plane was a brisk 2.7 seconds, but we were unable to lift the bow up, so its top speed only hit 20.4 mph — far short of its potential. The DF25A was a perfect match for compact pontoons designed for leisure cruising such as the Qwest 816, and it pushed the 816 to 15.5 mph.
The DF25A and DF30A are virtually identical except for engine mapping, which allows the DF30A to rev to a redline of 6300 rpm, some 300 rpm more than the DF25A. And thanks to an over-rev feature, you can’t damage either with excessive rpm. Suzuki clearly understands many owners will be running the engines close to WOT, because they didn’t sound the least bit taxed when asked go full throttle.
Suzuki’s DF25A/DF30A models have the Lean Burn Control System, which uses an onboard computer to predict fuel needs by monitoring engine performance and operating conditions to deliver a leaner fuel/air mixture to the engine whenever possible. The system results in a 15 percent increase in fuel economy over Suzuki’s previous models. On the Sea Ark, you can run the DF25A at 4000 rpm and still not even burn a gallon per hour (0.9 gph). At the Sea Ark’s happiest cruise speed of 19 mph, the engine is running at 5000 rpm and burning just 1.3 gph, netting an astounding 14.6 mpg.
You’ve Got a Friend
The last thing anyone wants to do after a long day on the water is spend a lot of time on cleanup, so Suzuki makes the engines user-friendly with a freshwater port. You can connect your garden hose for an easy, muff-less flush. Because the EFI system delivers fuel with greater precision than carburetors, one-pull starting is the norm, and Suzuki has even reduced the pull strength needed, thanks to its light-recoil starter.
Type: In-line 3-cylinder SOHC, 4-valve
Displacement: 489 cc (29.8 cubic in.)
Full throttle range: 5000-6000 rpm for the DF25A, 5300-6300 for the DF30A
Shaft lengths: 15 in. (DF25A only)/20 in. (both)
Weight: 136-163 lbs., depending on model
Gear ratio: 2.09:1
Price: To be announced
Tested with Sea Ark 1548 DKLD
Time to plane: 3.1 secs.
0-20 mph: 5.5 secs.
Top speed: 25.7 mph
Decibels @ idle: 53
Decibels @ 4000 rpm: 81
Decibels @ 6000 rpm: 89