Honda BF175 four-stroke

Until June 2002, all 175hp outboards available on the Australian market were two-strokes, whether carburetted, EFI or DFI. However, Honda changed all that with the introduction of its BF175, de-rated from the BF225, which in turn is based on the Honda Pilot four-wheel drive engine. Currently the BF175 is the only 175hp outboard to comply with California Air Resources Board (CARB) 2008 exhaust emission regulations.

As with its 225hp counterpart, there's the same variable air intake system, where below 3950rpm two valves in the air intakes remain closed, forcing air to resonate in the intake manifolds. This increases bottom-end torque and fuel efficiency, reducing trolling fuel consumption to around that of the Mercury Optimax 175.

At 3950rpm the valves open and the air intake is doubled, resulting in better performance above 4000rpm than motors with a non-variable air intake system. But oddly enough, Honda has omitted its brilliant VTEC system.

All the other features of the BF225 have been retained, such as the multipoint sequential EFI with oxygen sensor in the exhaust system to alter the air/fuel ratios according to barometric pressure, and a belt-driven 60amp alternator that still produces 48amps at only 1000rpm.

Also fitted is an under-cowl water separating fuel filter with a sight glass and high water level alarm at the front of the engine and a freshwater flushing facility to clear the cooling water passages of aluminium chloride crystals without running the motor.

Tested over two days on the Gold Coast Broadwater, the two BF175 demo motors performed faultlessly while pushing widely varying loads on two very different hulls. Both motors started instantly hot or cold, warmed quickly from cold and never blew any oil smoke. Vibration levels were extremely low at a slow trolling 650rpm, and across their entire rev ranges both motors were significantly quieter than the two-stroke competition.

However, in my opinion, both motors suffered from Honda's imprecise remote control box, which made judging whether or not the motors were in gear a bit of a pain. I've experienced this problem with other Hondas, so the company should consider doing something about improving the throttle/gearshift overlap in these boxes.

The first test hull was a Haines Hunter 585 Seeker, which displaced 1650kg including four adults. Spinning a 16in stainless steel Solas three-blade High Rake prop, the BF175 trolled at 5.0kmh consuming 1.4lt/h, and at 2000rpm - standard offshore trolling speed - averaged 12.0kmh using 6.1lt/h.

There's no doubt the additional 60kg weight of the BF175 over its Optimax 175 competition affected hull trim, and three-quarters throttle was needed to plane the rig at 25.0kmh on 2700rpm. At 4000rpm we averaged 50.0kmh using 32.7lt/h with no prop ventilation occurring through tight figure-eight turns at these revs.

"Flooring" the throttle lever at 4000rpm produced steady acceleration out to WOT, but less of the instant surge of the Mercury 175 models I've tested, which have been on bigger hulls and had coarser-pitch props. Across a 20cm chop the WOT average was 73.0kmh on 6000rpm consuming 67.8lt/h.

However, on an Ocean Cylinder 7.3m centre-console pushing a total of 1800kg including six adults and spinning the same-pitch Solas prop, the second BF175 achieved a clean plane at 29.0kmh on 3000rpm and averaged 62.8kmh on 5500rpm at WOT. Through tight figure-eight turns at 4500rpm there was no prop ventilation.

Access to components such as the oil dipstick, filler cap, spin-on oil filter and fuel filter is very good. Recommended servicing intervals are every 100 hours or once a year (when the waterpump impeller should be replaced) after the first 20 hours. I would change the oil and filter every 50 hours or six months.

At the time of writing, Honda's dealer network had not been provided with recommended servicing times so no servicing costs were available, but these would be about 50% higher per year than the direct DFI competition. The warranty coverage is three years for recreational applications.

With its under-stressed powerhead, the BF175 is better suited to commercial operations, and in my opinion should be used on hulls over 6m, which have the longer planing surfaces needed to handle this motor's weight.