Suzuki DF90

De-rated from its DF115 counterpart, the DF90 has more torque than any other four-stroke outboard in this power range. There are several factors contributing to this. One is that it has by far the largest piston displacement of any four-stroke of this output: 23 per cent over the Honda BF90 and 22 per cent more than the Mariner/Mercury F90, significantly reducing powerhead stress under most operating conditions.

Another factor is the sequential multipoint EFI compared to the competition's four carbies, enabling the DF90 to operate as efficiently on high-altitude alpine lakes as it does at sea level; and equally well on hot, humid summer days or cool, dry winter ones.

Finally, there's the two-stage gear reduction, achieved by offsetting the driveshaft from the crankshaft with a reduction in between, and an additional reduction in the gearcase where drive changes from vertical to horizontal. This enables coarse-pitch props to be swung without increasing gearcase diameter and hydrodynamic drag. Both reductions are chaindrive, as is the camshaft actuation: much more reliable than the belt drives of the BF90 and F90. Suzuki says the chains are designed to last the life of the engine.

The DF90's alternator produces 24amp more than the BF90's alternator and twice that of the F90's system, but then some of that current is used to power the computer-controlled EFI.

As with the DF115, the DF90 complies with the EU 2004 exhaust emission regulations scheduled to come into effect in January 2005. These are tougher than the CARB 2008 requirements and the DF90 is one of only four outboards in the world that currently comply (Suzuki's DF60/70 and DF115 are the others).

Of course, the main drawback of the increased piston displacement is the additional weight over the direct four-stroke competition, and in my opinion the DF90 is best suited to mounting on aluminium hulls with full-width transom pods and hulls over five metres in length. In standard longshaft form, the DF90 weighs 12 per cent more than the BF90 and eight per cent over the F90.

Tested on a 5.3m Clark Abalone Centre Console, the demo DF90 proved almost as quick as a DF115 on a Clark 5.7m Abalone, but appeared to develop more torque down low and was less sensitive to fore and aft weight distribution in the hull.

The DF90 started instantly hot or cold, never blew oil smoke and was so quiet when trolling it could barely be heard from the helm. Vibration levels across the entire rev range were very low. Power astern was excellent, assisted by the coarse-pitch prop, and no cooling water starvation occurred.

Spinning a 19in pitch alloy Suzuki prop and pushing a 950kg including three adults, the Suzy trolled at 4.8kmh on 650 revs using 1.1lt/h and averaged 6.5kmh on 1000rpm. The outboard planed us cleanly at 24.3kmh on 3100rpm regardless of whether occupant weight was amidships or concentrated just ahead of the transom.

The best cruising revs were 4000, where the Clark averaged 38.2kmh using 12.5lt/h. There was no prop ventilation through tight figure-eight turns at these revs despite the Clark having a long, deep keel, and there was no drop-off of revs due to the EFI compensating for the increased engine load.

The WOT average across a fresh afternoon chop on the Gold Coast Broadwater was 57.9kmh on 5600rpm - still slightly under-propped for this engine. At 30.5lt/h, fuel consumption was still very reasonable, and the engine was so quiet we could converse normally at the helm.

Powerhead access is good and the engine-oil dipstick and spin-on oil filter are easily reached. Recommended servicing intervals are every 50 hours, or six months after the first 20 hours, and the waterpump impeller should be replaced every 100 hours or once a year. The oil sump has sufficient capacity to effectively reduce oil sludging between oil/filter changes. A three-year warranty covers recreational applications.