Honda BF250 engine test: economic and powerful

Simon Everett takes Honda's latest BF250 engine for a test drive and finds out more about the engine's 'EcoMo'

30 January 2012.
By Simon Everett

The new Honda BF250 has been designed as a dedicated marine engine of 3583cc in a 60 degree V6 configuration utilising all their technological know-how. The mechanics are impressive, with bigger valves, lighter specially skirted pistons, a new crank and shorter conrods take the power from the pistons to the gears. The lower unit has also been improved, the gear case has been shaped for better laminar flow, and bullet shaped to reduce the drag by five per cent despite being of larger diameter to house the bigger gear wheels which provide a gear ratio of 2:1 for greater torque and improved fuel economy. The gears have been improved with finer tolerances and specially ground faces to reduce friction losses. Honda has gone down this route to allow the engine to use 16 inch propellers for heavy, work boat applications in addition to lighter leisure boat use.

Dual intake system
One major advancement on the BF250A is a radical, dual air intake system that separates cooling air from combustion air. There are two separate air intakes, one for cooling the electrical components, and the second purely for combustion. Two slash cut intakes on the top of the cowl provide air directly to the induction inlet tract via a moisture trap before ducting through the throttle body delivering cooler, denser air for better combustion and a 3hp benefit over standard cowling induction. The cooling fan draws the air in at the bottom and forces it out through the top after it has circulated the cowling

To run the plethora of electronics on a modern boat Honda has incorporated a very useful function into the high output alternator, their new idle charging system. Sensors recognise when there is a high demand on the alternator at low revs and automatically increase the engine speed by 100 rpm to generate an additional nine amps for charging, with about 30A available at 750 rpm and 40A by 1000 rpm batteries are kept in good condition, even in high load situations. These load sensors are used to take the load off the gears when changing gear, making a smoother transition from neutral to in-gear, either ahead or astern. The gear change is noticeably smoother and less clunky as a result.BF250

All the latest technologies are included, such as the holeshot enhancing BLAST.  For faster acceleration onto the plane the engine monitors sense the change in throttle position, at low revs, and adjust the mixture and ignition timing to boost torque until the engine pops out onto the plane, at which point the engine load sensors recognise the reduced load and readjust the settings for high fuel economy running. The BLAST engine settings are only activated when the throttle position changes fast, not if the throttle is set for slow cruising.

Testing it out
Once the boat is on the plane, the load on the engine reduces, allowing the electronic management to adjust the fuel mixture, valve and ignition timing for much leaner running. Honda call it EcoMo, it gives very economical cruising between about 3000rpm and 5000rpm, depending on hull shape and propeller choice, a green light within the tacho, or on the compatibly linked Garmin chartplotter unit, is displayed when the engine is running at these economical settings .

In practice the fuel efficiency of the Honda under the green light conditions is very frugal. We tried the motor on a variety of craft and the same was true on each one, the holeshot and economy whilst running on the plane was excellent. The boats we had were a couple of fast RIBs and a Ranieri 26-foot centre console. The Ranieri is quite a heavy boat being 1.5 tonnes with a single step to reduce the drag, she was on the plane in under four seconds and the economy light came on at just 2800 rpm at around 12 knots. For this boat the most economic speed was between 16.0 and 21.0 knots at 3000 – 3500rpm which returned 1.02 miles per litre.  At 4000-4500 rpm, 25.6 knots and 30.2 knots fuel consumption was 0.9 miles per litre. This averages to one mile per litre anywhere between 16 knots and 31 knots and proves the point about economy in the green light sector.

At idle the Honda is a bit louder than the Yamaha or Suzuki, but there is an odd benefit to this. On numerous occasions I have seen people go to start the engine, only to get a horrible grinding noise as the starter motor tries to engage with an already running motor. The Honda doesn’t require you to look at the tacho to see if it is started, there is enough idle noise to let you know she is running, but not enough to be intrusive.

Control is through a cable operated system, Honda are working on an electronic control, but until the saltwater longevity is proven they have opted for the reliability of cable operation. We have become spoiled with fly-by-wire throttle arrangements and I had forgotten how smooth a cable system could be. Combine the technology within the motor with the low drag of the new, stronger gearbox and transmission and you have a very stylish, well made, economical engine to hang on the back of your boat. Honda have really brought themselves into the mix with this motor.

SPECIFICATIONS

Engine Type 3.6L, 60°,V6,SOHC, 24V VTEC
Displacement 3583cc
Full Throttle HP Range 5,300 – 6,300 RPM
HP Rating at Prop shaft 250HP @ 5,800 RPM
Lean Burn Control Yes
BLAST Yes
Direct Air Intake Yes
Alternator Output 90-Amp
Gear Ratio 2:1
Dry Weight (inc St Steel Propeller) 278 kg (L) 284Kg (X) 288Kg (XX)

See also our US outboard expert Charles Plueddeman writing about 2012 Outboard News from Suzuki and Honda and our earlier news item New Honda Makes its Debut.


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