Stress less

Released on the Aussie market in September 2008, the current DF70 has 16 per cent greater piston displacement for four per cent less weight than the old model.

Although it develops the same power at the same rpm, it has a broader Wide Open Throttle rpm range to allow for greater variations in hull loading.

Whereas the old DF70 was based on the Suzuki Sierra 4WD engine, The Haines Group said the current model powerhead is designed specifically as a marine engine. Subsequently, it has larger diameter bearings than Suzuki auto engines in this displacement range to handle the greater loads this engine will be subjected to.

Unlike the old engine's eight valves operating off a single belt-driven overhead camshaft, the current model has 16 valves and double overhead chain-driven camshafts for improved breathing efficiency and longevity. Previously only available from 90hp upwards, the DF70 also has Suzuki's two-stage gear reduction system that places the crankshaft farther forward for better weight distribution on the transom and reduced gearcase size to improve hydrodynamic performance.

Gear-driven from the crankshaft, the primary reduction is 1.24:1 and the secondary or right-angle reduction in the gearcase 2.09:1, the same as engines like the DF25. This results in an ability to swing coarse-pitch and thrust-efficient (for planing hulls) props without enlarging the gearcase torpedo.

Other design and mechanical changes include re-designed lower unit with forward-angled leading edge to the torpedo, which according to Suzuki, reduces hydrodynamic drag by up to 36 per cent, while the re-designed lubricating oil pump and oilflow passages reduce frictional losses.

IMPROVED START-UP
Starting the DF70 is easier than the old model due to a system that engages the starter motor by simply turning the ignition key to "on" and then releasing it, instead of holding it on as before. Shifting into forward or reverse is also made smoother by retarding the ignition timing during these actions.

By using a 32-bit engine management computer, Suzuki has incorporated a lean-burn system in the DF70 to increase the air/fuel ratio at midrange revs, though Suzuki has not specified the rpm range. The under-flywheel alternator is air-cooled for longevity and produces 22amps at only 1000rpm, but around five amps are needed to power the engine management computer and fuel injection system.

Mounted on a fibreglass Seafarer Vantage 485, spinning a 19in stainless steel prop and pushing 750kg, the DF70 was well matched to this 90hp rated hull.

It started instantly hot or cold and didn't blow oil smoke, nor was there an oil smell backing upwind. The new starting and shifting systems worked very well with no "clunk" when shifting into gear. Providing the antiventilation plate was kept at least three-quarters immersed, power astern was good and no cooling water starvation occurred.

The DF70 trolled us at a low 3.8kmh and 700rpm using 1lt/h with similar vibration levels to the old DF70 and current Honda BF75. Clean plane was realised at only 19.3kmh and 3000rpm, although, when "floored" from trolling rpm we planed in less than five seconds.

Cruising quietly at 4000rpm averages were 44.5kmh and 9lt/h. No prop ventilation occurred through a full-lock figure of eight turns at these revs. At 5000rpm we averaged 56.0kmh, and 63.8kmh and 22lt/h at WOT of 5700rpm where we could talk normally at the helm. Vibration levels at these revs were low.

Powerhead access is good with the oil dipstick, oil filler cap and fuel filter easily reached, although oil filter access is not as good as the BF75. And as the oil sump capacity is 11 per cent less than the old DF70, to prevent sludging during extended trolling, the oil and filter should be changed at intervals no greater than 100 hours or yearly when the waterpump impeller should also be replaced. The first service is at 20 hours.

The DF70 has a five-year recreational-usage warranty and meets OEDA 3 Star exhaust regulations.