Volvo Penta D6-350 Diesel Stern Drive

Volvo Penta's D6 marine diesel is available in both 310 and 350 horsepower model and in both inboard and stern drive configurations

Krossholmen, Sweden: You probably already guessed the new high Volvo Penta marine diesel is common rail, direct injected and that its manners are impeccable. It's indisputably quiet. It does not rattle and clatter like a conventional diesel. Its exhaust is virtually smokeless. Even for a diesel, its fuel consumption is miserly.

Volvo Penta D6-350 horsepower marine diesel

With all that going for it, what's particularly tantalizing about this new power package is the recipe Volvo used to pump up horsepower. The D6-350 DP draws its breath through both a supercharger and turbocharger. Pushing the throttle lever forward causes a clutch to engage the supercharger, instantaneously forcing a huge mass of cooled air down the engine's throat. The cooler the air, the greater its oxygen content. The greater the volume of airflow, the more fuel the crankshaft can spin into gold. All the while the revs are climbing, the turbocharger is spooling up like a little jet engine. At about 2300 rpm the turbocharger catches up and the supercharger clutch disengages.

What this scenario means at the helm is as simple as a common, grey iron casting. Throttle response is razor sharp. With the immediate boost from the supercharger, turbo lag dissolves into a feint memory of the way diesel engines formerly behaved. Instead of boggy acceleration, the boat leaps up onto plane on so quickly you'd swear you were holding the reins of a high performance gasoline engine. Only, diesel engine fuel economy is about double that of a gas engine and engine life is vastly extended.

This recitation is hardly untested theory. I evaluated Volvo's new motor on a variety of boats on location in the North Sea. During one of the tests we pushed so hard we broke a Swedish Coast Guard patrol boat. First the helm seat broke. Next the companion seat cracked. With all the smashing into the waves and throwing water a lifting strake broke loose and we had to go on the hard to repair the damage. Lest you think we were being reckless, this was a vintage craft built in 1988 with more than 120 thousand miles under her keel. Before retirement the battle scarred veteran had been re-powered to measure the performance and reliability of the new Volvo inboards. We were simply testing it in real world conditions.

So what kind of boats can we expect to see these new engines power here in the US? Volvo's new D6-350 DuoProp is intended for twin installations in flybridge boats and sport cruisers up to about 45 feet. Note the DP in the nomenclature means DuoProp, or where the drive leg spins a pair of counter-rotating propellers. The two props on one axis configuration transfers more horsepower into forward thrust than a single propeller. Added blade area also lends the driver more control over the boat.

There's a variation on the DuoProp theme, one intended for fast flyers capable of 47 to 60 knots. The D6-350 DPR drive leg is virtually identical to the DP, but its lower unit housing is profiled for higher speeds and the shaft splines are fitted with stainless steel propellers. Targa 40 motoryacht with twin Volvo D6-350s.

Inboard boat builders need not be left out in the cold. For them Volvo's D6-370, rated 370 hp, features a choice of either an electronically controlled hydraulic reverse gear or a V-drive. It's also important to note the D6-370 inboard does not draw its breathe through a supercharger. Its multitude of horsepower is built solely via turbocharger.

Finally, both of these inboard and sterndrive engines oil-cool their turbocharger bearings; the turbo housing is water-cooled. Fastidious cooling prevents hot exhaust gases from baking lubricant into carbon, an abrasive which would otherwise destroy the turbo bearings. Suffice it to say these engines not only run hard, they're built to last.

Targo 40 MotorYacht with twin Volvo Penta D-6-350s: Full fuel, speed clocked by GPS, on flat seas with a 5 mph breeze and two men on board.

rpm

Speed (knots)

gph

MPG (Nmpg)

600

4.6

0.5

.12

1000

7.4

2.4

.32

1500

9.6

7.0

.73

2000

14.4

13.4

.90

2600

26.4

18.5

.70

2800

30.0

20.3

.68

3000

32.8

23.2

.70

3200

35.8

28.8

.77

3400

38.8

31.2

.80

3525

40.2

34.5

.85