words - Andrew Norton
At last there's a pocket diesel sterndrive to rival MerCruiser's successful 135hp DTI 1.7L, says Andrew Norton

It's been some two and half years since I first tested the MerCruiser D1.7L DTI turbo-intercooled diesel sterndrive, and since then I've been asking Mercury Marine when it would develop a more powerful version, and Eastern Engine when Volvo Penta would release an engine to counter Mercury's gem.

Well, Volvo Penta has finally responded with the release of its direct injection D3 at the Sydney Boat Show - the smallest of a new generation of Aquamatic diesel engines. Available in two versions delivering 129 and 161hp at the crankshaft, the D3 has an all-alloy five-cylinder powerhead and high pressure common rail fuel injection that enables it to comply with 2006 EU and US EPA regulations for oxides of nitrogen emissions. The more powerful version produces 29 per cent more torque than the MerCruiser 1.7, yet with standard SX drive weighs just five per cent more.

To achieve 161hp from 2.4lt of piston displacement and maximum torque from relatively low revs without resorting to supercharging, Volvo Penta has opted for "Variable Geometry Turbocharging", where the turbine blade pitch is electronically altered to make the best of the gas flow available. Volvo Penta says that at low revs, a turbocharger that can quickly reach high revs will produce more torque down low, while at high revs the turbine should be of adequate capacity to take full advantage of the much greater gas flow.

The end result is an engine that develops a massive amount of torque for its displacement and a flat torque curve for 750 revs. The maximum torque of 340Nm is produced from 2000–2750rpm, and by 1750rpm the output is 339Nm - whereas the MerCruiser 1.7 produces a peak of 264Nm at 2400rpm.

The D3 engine measures 713mm long, 654mm wide and 684mm high compared to 726 x 746 x 689mm for the MerCruiser 1.7.

Whereas the MerCruiser 1.7 has mechanical fuel injection with fixed timing, the D3 has electronic engine management 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 with 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. EVC also provides constant engine output regardless of ambient temperature (5–55°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 load.

Unlike the Alpha drive used with the MerCruiser 1.7, the standard SX drive has a cone clutch for smooth shifting into ahead or astern gear.

I recently talked to Simon Miller of Fleet Marine in Melbourne - a Four Winns dealership that offers the choice of MerCruiser or Volvo Penta power. He said the smoothness of the SX gearshift was winning plenty of buyers.

So far the only Aquamatic from the new range I've been able to test has been the D6 - not exactly a trailerboat engine. But based on figures supplied by Volvo Penta, at 2000rpm the 129hp D3 consumes 5lt/h compared to 4lt/h for the MerCruiser 1.7. At 2750rpm, 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.

Powering up to 4000rpm, 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 appeared the D3 had the advantage in the upper rev range - most likely because fixed injection timing diesels retard above their optimum injection rev range, normally around where maximum torque is produced.

Engine type: Crossflow DOHC 20-valve turbo intercooled diesel
Prop hp/rpm: 123.3/4000 & 154.2/4000
Max crankshaft torque (Nm/rpm): 280/1750–3000 and 340/2000–2750
Piston displacement (cc): 2400
Bore x stroke (mm): 81 x 93.2
Injection: Direct
Cooling: Closed circuit (heat exchanger)
Oil type: SAE 15W40
Gear ratio: Both 1.66:1
Dry weight including SX leg (kg): Both 310
For more information contact Eastern Engine, tel (07) 3902 5444

Published : Wednesday, 1 October 2003

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