A couple of years ago, TAB published details of Volvo's Kompressor range of diesels, some of the most innovative marine engines ever produced.

Volvo's Kompressor system comprises a belt-driven air compressor (supercharger) in addition to the normal turbocharger and intercooler system. When the throttle is rapidly opened, the supercharger is engaged by an electromagnetic clutch, compressing air and forcing it through the turbocharger. Once the turbo has reached its normal boost pressure, the supercharger is disengaged while the turbo takes over. At that point, a non-return valve in the intake manifold prevents air from passing through the compressor.

When the revs fall below around 2400rpm, the compressor cuts back in as the turbo starts to fall off boost, keeping overall boost pressure relatively constant compared to non-Kompressor engines. This system enables a boat to maintain a clean plane at lower revs and reduces both fuel consumption and black exhaust smoke from fuel oversupply at low revs under load.

When the Kompressor article was compiled in October 1998, two six-cylinder models were available, both based on the long-running 3.6lt powerhead. The mechanically-controlled KAMD43P developed 230hp, while the KAMD44P Electronic Diesel Control (EDC) model developed 260hp. The latter model has been the standard powerplant in the Riviera 3000.

But due to US demand for more power for the same weight, particularly for boats such as the Riviera 3000, earlier this year Volvo developed the 24-valve KAMD300 and KAD300/DP, both based on the 3.6lt engine and fitted with EDC as standard.

The KAMD300 is an inboard engine and develops 202kW (271hp at 746W = 1hp) at the propshaft and 210kW (282hp) at the crankshaft. The Duoprop-equipped KAD300/DP develops 200kW (268hp) and 210kW (282hp) respectively. Both models develop maximum power at 3800rpm.

The direct-injection 3.6lt powerhead has bore and stroke dimensions of 92 x 90mm, making it an over-square engine - unusual for a diesel. The compression ratio is a relatively low 16.5:1 and the cast-iron cylinder head and block and the reliable pushrod valve actuation have been retained from earlier models. Replaceable valve seats and wet cylinder liners are fitted and the crankshaft has seven main bearings.

The turbocharger is cooled with freshwater for reliability, and has an intake manifold filter to prevent dust entry, while the cast-iron seawater-cooled exhaust elbow has a stainless steel insert for improved corrosion resistance.

The fuel injectors are reliable, five-hole units and fuel is supplied via water-separating filtration. A hand pump is provided for initial priming of the fuel system. The oil filter is easily replaced and the tubular oil cooler can be cleaned, while to reduce blow-by gas emissions, the crankcase vents into the intake manifold.

The alternator produces 60amps at 14V and is fitted with special diodes that protect the charging system from voltage peaks, while the starter motor develops 3kW - 20% more than Yanmar's 4.2lt 6LP-STZE diesel, which, in my opinion, is the main competition to the KAD300/DP.

As with its predecessors, the new models are compact. In bobtail form, the inboard version measures 1221mm long, 789mm wide and 734mm high, while the standard single-speed HS63AE gearbox, with 8? down angle, adds just 169mm to the overall engine length. This unit can safely freewheel for up to 24hrs without affecting gear and clutch lubrication.

Volvo does not provide a bobtail-only weight, but complete with the gearbox, the dry weight is 539kg - only 1kg more than the KAMD44P EDC.

According to Eastern Engine's Graeme Avers, about 80% of Volvo diesels sold in the 150-300hp range are sterndrives and the KAD300/DP has in-boat measurements of 1244 x 788 x 734mm and, complete with drive unit and power steering, weighs 576kg. The drive unit can be tilted up 42? to clear the boat's bottom, though this is still 13? less than the dual-prop Bravo 3 drive fitted to Yanmar's 6LP-STZE.

Yanmar's 6LP-STZE develops 221kW (296hp) at 3800rpm and has 24 valves actuated by a belt-driven SOHC. The in-boat dimensions of this diesel are 1145 x 699 x 812mm and, complete with drive unit, it weighs 526kg.

But although the Yanmar complies with current IMO exhaust emission regulations, it still has a mechanically-controlled fuel injection system.

In comparison, both the KAMD300 and KAD300/DP have Volvo's Electronic Diesel Control, which has proven to have excellent reliability in truck engines and, according to truckies interviewed, has reduced fuel consumption 40-50% over mechanically-controlled Volvos.

In 1995, EDC was launched into the marine diesel market and has proven popular in recreational cruiser installations, for EDC has a number of advantages over mechanical control. It ensures that the injection timing is accurate at all revs, instead of being either too advanced or retarded, depending on which side of the maximum torque zone a diesel is operating.

In Volvo's Kompressor range, the EDC acts as a torque controller to ensure a seamless transition from compressor to turbo and back again. According to Graeme Avers, this virtually eliminates the need for a two-speed gearbox in pleasure cruiser installations.

Other advantages include the correct air/fuel ratios, regardless of barometric pressure, enabling the engines to operate as efficiently on a hot summer's day as they do in mid-winter, when the air is much denser. The system also compensates for temperature variations, from 5-55?C , to maintain maximum combustion efficiency.

Both engines have a self-diagnostic facility accessed via a laptop computer, which downloads a record of engine hours, operating cycles and any problems such as injector blockages or engine overheating.

Shifting from neutral to ahead or astern is smoother than fixed-timing diesels as the EDC maintains a lower, more stable idling speed. And as the shift control is electronic, rigging remote controls is easier and engine vibration transmitted along these to the helm station(s) is eliminated. The EDC system simply plugs together for rapid installation and servicing.

As with their less powerful counterparts, these new Volvos offer a different approach to pleasure boat diesels, but still retain commonsense engineering that should ensure a long engine lifespan.

For more on these motors, contact Eastern Engine, tel (07) 3899 1622.