Honda BF90D outboard motor review

Originally published in TrailerBoat #246, July / August 2009

The Honda BF90D outboard motor was released onto the Australian market in September 2006. Based on the Honda Jazz car engine, it was designed to replace the long-running Honda BF90A, which was based on the 1.6lt Honda Civic car engine, but had four carbies instead of multipoint EFI.

HONDA BF90D

Although the Honda BF90D outboard motor has 94cc lesser piston displacement, it develops more torque and delivers much better upper rpm-range performance thanks to its multipoint EFI and VTEC. Unfortunately, since it activates at 5200rpm, the overall performance is not much better than the Honda BF75D. However, the addition of BLAST (Boosted Low Speed Torque) and lean-burn technology helps overcome the usual relatively lacklustre midrange performance of four-stroke engines compared to DFI two-strokes, unless Variable Intake Valve Timing is fitted.

What is the BLAST system? It advances the ignition timing depending on the throttle opening to develop more horsepower and torque. This allows the hull to quickly plane while the air/fuel ratio is much leaner than normal when running between 2000 and 4500rpm. Again, this depends on throttle opening and in this rpm range it hits around 18:1 instead of the normal 14.7:1.

To cope with higher onboard electrical loads, the flywheel alternator output on the was increased from 20amp in the Honda BF90A to 44 with up to 35amp for dedicated battery charging. An Engine Alert System in the control unit constantly monitors engine coolant overheating, low-oil pressure, over-revving (6500rpm), water in the fuel system and battery condition (like all of the four stroke-competition). After all, effective ECU operation is dependant on a healthy battery.

PERFORMANCE

Some time ago, Honda MPE tested a Honda BF90D outboard motor on a hull that showed off the engine’s true performance potential. Mounted at the highest transom setting on a Makocraft Estuary Tracker Tournament 480 and spinning a 22in Solas stainless steel prop, the demo BF90D had no trouble pushing 1000kg including a bow-mount Minn Kota trolling motor, two hefty deep-cycle batteries, two adults and full fuel.

The engine started instantly hot or cold and did not blow any oil or smoke, nor was there an oil smell when backing upwind. Providing the anti-ventilation plate was kept at least three-quarters immersed, power astern was good and no cooling-water starvation occurred. The power trim and tilt also worked quickly and quietly.

Trolling at an almost vibration-free 750rpm, the BF90D averaged just over 2kts using 1lt/h. Holeshot performance, when we opened the throttle rapidly, was not as good as a BF75D on a Stacer 489 Easy Rider due to a fair amount of prop slippage from the high engine mounting. Still, a clean plane was achieved at just over 14kts and 2800rpm, with a minimum cruise of just over 16kts using 8.5lt/h at 3000rpm.

Ideal cruising efficiency was at 4000rpm, with an average of 25kt using 9.6lt/h. However, at this rpm and even with the leg trimmed right in, some prop ventilation still occurred through full lock figure-of-eight turns. Even so, this was more than compensated by straightline performance, with acceleration improving considerably from 4000rpm to 5000rpm as the big prop bit in. The averages at my recommended maximum cruising rpm of 5000 were 33.5kts at 18.3lt/h.

When the throttle was floored, the tacho almost jumped instantly to more than 6000rpm with impressive WOT averages of 43kts and 27.5lt/h at 6200rpm.

Considering it was a tinnie, what really blew me away was the way the leg could be trimmed out to the trim-section limit without any prop blowout. The engine was also relatively quiet at WOT.

MAINTENANCE

Finally, powerhead access is excellent with the engine-oil dipstick, canister-oil filter and spark plugs easily reached. Recommended servicing intervals are every 100 hours or annually after the first service at 20 hours.

Technical information on the engine’s emissions supplied by Honda shows that the BF90D easily meets with OEDA 3-star exhaust emissions compliance ratings. The warranty is five years for recreational usage.

HONDA BF90D SPECIFICATIONS

* As per manufacturer’s recommended schedule including oil filter and oils, but excluding other parts. All prices current as of June 09. Demo BF90D from Honda MPE, Campbellfield, Vic. Phone (03) 9270 1111 for more information.

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Originally published in TrailerBoat #246, July / August 2009