Volvo Penta D3

A couple of years ago we reviewed the turbo-intercooled MerCruiser DTI 1.7L as a repower alternative to petrol sterndrives for hulls such as the Caribbean Bertram 26. Since that article appeared, the MerCruiser has also proven popular in Bertram 25s due to its compact dimensions and relatively light weight.

But after two years of having the market to itself, the 1.7 now has a serious contender with the recent release of the Volvo Penta D3 - an all-alloy five-cylinder 2.4lt diesel based on the engine in Volvo's X90 4WD station wagon.

The direct-injection turbo-intercooled engine complies with both the US EPA and EU 2006 oxides-of-nitrogen emission levels.

OUTPUT, TORQUE & ENGINE MANAGEMENT
The engine is available in two versions - the 130/SX, which develops 129hp at 4000 revs - and the 160/SX, which develops 161hp at the same revs (both crankshaft outputs based on 1.0hp = 746W).

The 130 produces 280Nm of crankshaft torque from 1750-3000 revs, and the 160 a massive 340Nm from 2000-2750 revs - whereas the 120hp MerCruiser 1.7 has a fairly "peaky" torque curve and produces a maximum of 264Nm at 2400 revs.

To achieve this with a relatively low 18:1 compression ratio, the D3 has 20 valves driven by double overhead camshafts for effective "breathing". And instead of fitting a supercharger for increased bottom-end torque compared to straight turbo-intercooled diesels - as was done with the KAD series of diesels - Volvo Penta opted for "Variable Geometry Turbocharging".

The turbine blade pitch is electronically altered to make the best of the gas flow available, and Volvo Penta says that at low revs, a turbocharger that can quickly reach high revs will produce more engine torque down low - while at high revs, the turbine should be of bigger capacity to take full advantage of the much-greater gas flow.

Whereas the MerCruiser 1.7 has mechanical fuel injection with fixed timing - which limits engine efficiency - the D3 has electronic engine management with variable injection timing and was designed to be used in conjunction with Volvo Penta's EVC (Electronic Vessel Control), which offers a level of engine and instrument integration not previously available to sterndrives of this output.

EVC offers speed, fuel-tank level, depth and surface water temperature in addition to engine revs, fuel flow and comprehensive warning systems. It also provides constant engine output regardless of ambient temperature (five to 55°C) and fuel density.

To prevent the operator damaging the engine by demanding full power when the engine is cold, the revs are increased in stages as the engine approaches normal operating temperature. Should the throttle be "floored" straight after the engine is started, the revs will increase to 1200 and stay there until the management system decides the engine is sufficiently warm to handle more revs and load.

The voltage-regulated alternator produces a maximum of 140amp to power the engine management system and a myriad of onboard electronics.

A BETTER DRIVE
Unlike the old Alpha drive used with the MerCruiser 1.7 - which has a dog clutch in the gearcase - the standard SX drive has a cone clutch for smooth shifting into ahead or astern gear.

Positioning the clutch at the first right angle and in many cases above the waterline ensures that if water does enter the drive leg, it's less likely to corrode the clutch. Servicing access is also better.

Recently I talked with Simon Miller of Fleet Marine in Melbourne - a Four Winns dealership that offers the choice of MerCruiser or Volvo Penta power in its boats. He said that due to the smoothness of the SX drive, which didn't require ramming into gear to avoid damaging the clutch dogs, many buyers were favouring Volvo Penta - even the 135hp model - over MerCruisers for this factor alone.

A much newer design, the SX also has a much better hydrodynamic shape for reduced high-speed drag, and comes standard with power steering - whereas this is an option on the Alpha leg.

The SX drive has a 1.66:1 gear ratio compared to 2.00:1 for the Alpha leg, but as the 130 and 160 develop maximum power at 400 to 600 fewer revs, the prop revs will be similar.

SMALL PACKAGES
Both the 130 and 160 have engine-only measurements of 713mm long, 654mm wide and 684mm high - more compact than the MerCruiser, which measures 726 x 746 x 689mm.

This means that the 130 and 160 have a smaller footprint, and the 92mm lesser width makes a significant difference to servicing ease - particularly in the Bertram 25, where the engines were mounted very closely together.

In the Bertie 26, which is designed for V6 engines instead of inline fours or sixes, the servicing access would be even better!

Because Volvo Penta uses automotive-style but waterproof connectors, wiring up the 130 and 160 should be relatively straightforward. And at 310kg complete with SX drive and closed circuit (heat exchanger) cooling - as has the MerCruiser - the weight is only five per cent more than the DTI 1.7L.

NON-DRINKER
So far, the only Aquamatic from the new range I've been able to test has been the D6. But based on propeller power curve figures supplied by Volvo Penta, at 2000 revs the 130 consumes 5.0lt/h compared to 4.0lt/h for the MerCruiser 1.7. At 2750 revs, where the MerCruiser 1.7 demo engine achieved a clean plane, it used 7.5lt/h compared to Volvo Penta's claim of 11lt/h at these revs, while cruising at 3000 revs the MerCruiser 1.7 used 9lt/h compared to 13lt/h.

Increasing the revs to 4000, the MerCruiser 1.7 consumed 17lt/h compared to 26lt/h for the D3 at the same revs. However, as the MerCruiser 1.7 ran out to 4600 revs using 27lt/h, it appears the D3 has the advantage in the upper rev range - most likely because fixed injection timing diesels run too retarded above their optimum injection rev range, normally around where maximum torque is produced.

For more information on the D3, contact Graeme Avers at Eastern Engine, tel (07) 3902 5444 or email: graeme.avers@volvopenta.com.au.