Posted: November 1, 2011
New BF250 possesses everything good about Honda engines.
When it comes to outboard engine development, Honda has been anything but rash. For nine years, the company’s biggest outboard has been the BF225, which has met with critical acclaim for its performance and reliability. But it was being left in the dust by the upward march of bigger, badder four-stroke outboards from other manufacturers that now get to 557 hp. Honda has now reached critical mass with its new BF250, which is big enough to power the ever-lengthening outboard-powered boats on the market. The look is all-new, with a predatory shape and breathing vents that give it a visage not unlike the non-human star of the movie “Alien.”
The one thing Honda wasn’t going to do by going larger was jeopardize its sterling reputation for reliability, and nothing showcases its ability to build bulletproof motors like its IndyCar engine program. Honda has been the sole provider of powerplants for the IndyCar Series since 1996, and during the last four Indianapolis 500 races there have been zero engine failures. Before that stretch, there had never been an Indy 500 without an engine failure. In 2009, the only engine failure for the entire season — during which drivers racked up 202,210 miles of racing and practice — was the result of a broken alternator wire. That’s positively preternatural when you consider they run at engine speeds of more than 10,000 rpm. The mechanical lessons learned translate well, because the only thing more demanding than the racetrack is the marine environment.
Big and Beefy
The BF250 is designed to be a heavy-haul workhorse with its new gearcase design that has a 10 percent larger gear wheel. This allows the Honda to feature a 2:1 gear ratio, which is shorter than all other 250s on the market except the Suzuki DF250. The engine’s gear ratio allows it to swing a larger-diameter 16-inch prop, giving it more thrust to push heavier boats with ease. Despite the larger gear wheel, Honda managed to reduce the drag coefficient of the lower unit by 5 percent for better fuel economy and higher speeds.
The all-new block is 3.6L, which allows it to produce 250 hp without breaking a sweat. Although the two motors aren’t related, by comparison, the Honda IndyCar engine is slightly smaller at 3.5L while cranking out 650 hp. Many Honda engines in the larger power range are marinized auto engines, and the 3.6L follows suit but steps up in class. The BF225 is basically an Odyssey minivan engine, while the new BF250 is derived from Honda’s Acura line of luxury cars. It even runs on regular 86 octane gas rather than premium.
Putting It to the Test
During a sneak preview in central Florida near the land of a famous rodent, we were set up to test the BF250 on three distinctly different boats: a Hurricane 231 center-console deckboat, a JC SportToon 23 TT pontoon and a 295 Everglades center-console offshore fishing boat powered by twin engines. Thanks to a typical Florida thunderstorm that quickly appeared and dropped visibility to Mr. Magoo range, I could only conduct a full test on the first two boats.
As expected, the Honda was ultra-quiet, measuring just 56 decibels at idle on both boats. Also not surprising was the lusty acceleration out of the hole, thanks to BLAST (Boosted Low Speed Torque) technology, which aggressively advances the ignition timing while increasing the amount of fuel in the air/fuel mixture to prevent knocking. Our time to plane on the Hurricane was 3.4 seconds, slightly more than the JC SportToon, which clocked in at 3.1 seconds thanks in part to the lifting strakes on its U-shaped tubes. BLAST is only engaged when, like us, you jam the throttle wide open quickly, which is smart, because enriching the air/fuel mixture reduces your fuel economy — there’s no free lunch. But for getting out of the hole quickly, it’s a handy tool to possess.
Honda gives the BF250 added kick in the midrange with its Variable Air Intake system, which features a butterfly valve that opens when you hit 4000 rpm and changes the shape and volume of the intake air chamber. At slower speeds, it’s U-shaped, and the air flows through tuned pipes to supply the correct amount of air. When the valve is opened, the area in the chamber between the “U” is filled in; it looks more like a whiskey jug silhouette and increases the volume of air that is supplied by inertia. You can actually feel a boost of power when the butterfly valve opens, something that allowed us to record quick 0-to-30-mph times on both boats. The Hurricane took just 6.3 seconds, while the JC pontoon accomplished it in 2 more seconds.
Most outboards with a flat power curve tend to have a “square” bore vs. stroke, meaning the numbers are very similar. Often when we do boat tests, we’ll get a boat up to 90 percent of its top speed quickly, but then it takes about 10 seconds to wring that last couple of mph out of it. The BF250, however, has a slightly “under square” design at 89mm by 96mm, which helps it perform well at lower engine speeds. Without something to give it some pop at the upper rpm range, you would have an engine that was great at cruising speeds but would lack punch when you dropped the hammer. Borrowing a design first featured on the Honda NSX, perhaps one of the coolest sports cars ever built, the BF250 employs VTEC (Variable Valve Timing and Lift). When it reaches the upper rpm range, pins are hydraulically actuated that link all of the rocker arms together to utilize different lobes on the camshaft, which changes it into something resembling a racing cam, wringing every last bit of speed out of it.
VTEC pushed our test Hurricane to a top speed of 49.4 mph at 6300 rpm. The JC pontoon peaked at a respectable 44.6 mph with a top rpm of 6200. Sound levels on both were measured at 93 decibels.
I suspect the BF250 is only the first incarnation of this engine we will see. Although Honda has said nothing about higher horsepower configurations, I wouldn’t be surprised to see this pumped up to 300 hp with only some tweaking of the onboard computer. But as we’ve seen, Honda will do nothing until it’s sure you can shoot bullets at it.