words - Andrew Norton
Volvo's latest 'smart' diesel ­ the TAMD 74P EDC is no longer truckies' best-kept secret. Its benefits of low emissions, reliability and fuel economy are now available to mariners as well. Andrew Norton

Adding together sophisticated electronic engine management and diesel, while retaining a relatively mechanically simple motor, is one way of meeting strict exhaust emission regulations.

This in summary, is exactly what the new Volvo low-emission TAMD 74P EDC is, a proven terrestrial diesel that's been re-engineered to suit a variety of marine applications.

Volvo's new low-emission truck-origin diesel slots in neatly between Yanmar's 420 hp 6LY2-STE and the 660 hp Cat 3196 and 635 hp Cummins QSM11.

There is nothing wrong with using truck diesels in marine applications.

Most heavy truck diesels have features which ensure a long service life and the ability to be overhauled at least a couple of times.

The 74P EDC is no exception and has lots of good features like replaceable wet cylinder-liners and valve seats/guides, two separate cylinder-heads with a flame barrier between them to protect the head gasket as well as 12V or 24V electrical system with 60 amp alternator.

The fuel system is designed to handle ambient temperatures from 5-55°C and features six-hole injectors for efficient fuel spray and lower emissions.

There's even an oil dipstick on both sides of the engine for ease of maintenance in marine applications.

Most truck engines develop maximum power at moderate revs and maximum torque well down in the rev range. This provides plenty of 'grunt' for planing larger gameboats and cruisers.

The 74P EDC develops a maximum of 480 hp at 2600 revs, 14% more than Yanmar's 6LY2-STE but at 700 fewer revs.

The long stroke (135mm compared to the 107 bore) powerhead develops maximum torque of 1432Nm at just 1600 revs, 29% more and 900 revs lower than its more compact Japanese rival. Even at 1000 revs the Volvo develops 730Nm of torque.

These outputs are not bad for a motor that has a piston displacement of 7.28lt.

The low revs at which maximum torque is developed also makes the motor particularly flexible. More so when matched with one of ZF's two speed gearboxes.

A suitable model is the electronically-controlled ZF IRM 300 ATS, which has a 7° down-angle output flange and weighs 116kg, 69kg less than Volvo's own single speed electronically-operated hydraulic gearbox.

According to ZF, overall the best ratios for planing hull application would be the 2.000:1 in first and 1.567:1 in second combination.

Building a diesel which can handle severe operating conditions does however, increase its weight. At 860kg in bobtail form (sans gearbox), the 74P EDC is 67% heavier than Yanmar's 6LY2-STE. From flywheel to alternator drive-belt pulley, the 74P EDC is 1142mm long while the overall width is 794mm and height a fairly imposing 937mm.

The fuel economy of Volvo's EDC (Electronic Diesel Control) is another plus.

Recently, while editing my first industrial newspaper, I talked with truckies who had switched to electronically-managed diesels. They all said their savings were enormous. One coal truck owner-driver told me his fuel savings were 40%, compared to operating a fixed injection-timing diesel.

A glance at Volvo's 74P EDC fuel consumption graph shows a similar story. According to Volvo, at maximum torque and based on propeller power curves, the 74P EDC consumes just 27lt per hour (edited 31/1/13. See readers note below. Original figure is incorrect. About 100 litres/hour sounds right.)

Contrary to concerns among engine operators about reliability of the electronic engine management components, again from interviewing truckies, a well-designed system does not create a weak link in the powertrain system. For example: the coal truck drivers who were interviewed said they had experienced no more downtime than with conventional diesels. This was despite operating vehicles on dusty and rough roads.

In marine applications, it's just a matter of building-in thorough waterproofing, in addition to vibration isolation.

Volvo first introduced EDC to its marine diesels in 1995, and according to the company, the system has been designed to withstand the harsh marine environment.

The control unit for the EDC system is 'baked' in polyurethane plastic, then placed in a diecast aluminium box and engine-mounted.

The fact the control unit is engine-mounted with provisions for plug-in throttle and gearshift control cables, makes the engine easier to install than 'conventional' diesels which require mechanical linkages.

The EDC system and control unit constantly monitor the status of major engine components. Information is computed continuously to determine the precise quantity of fuel required at any given moment.

It takes into full account all variations in operating temperature, barometric pressure and other fringe factors in order to maximise engine efficiency.

According to Volvo, in tropical climates the EDC system compensates for high fuel temperature to avoid power loss.

It also reduces exhaust smoke to a minimum, especially when compared to fixed timing diesels, where there is always some fuel over-supply on start-up. Underway it's claimed to provide better throttle response and lower, more stable idling important for low-speed manoeuvring in marina confines.

Volvo's gearboxes are available (as are the ZF units) with a trolling valve that allows some 'slip' in the transmission, further reducing revs at the prop and subsequently boatspeed.

Because electric control cables replace mechanical ones, much less force is needed to operate the controls, and no engine vibration or noise is transmitted through the cables to the helm station.

Volvo claims it is much easier to rig the boat should multiple (eg: upper, lower and tower) helm stations be required and maintenance of these components is reduced, due to fewer moving parts.

Last but not least, the EDC can be used to automatically synchronise engines in dual installations.

Should a malfunction occur, a flashing code is displayed on the operator's control panel.

Eight major parameters of information are stored and may be accessed by a technician using a diagnostic key.

Examples of information stored relate to adequate engine cooling capacity, sufficient air supply and correct matching of propeller to load.

Taking all of the above into account, there's no doubt Volvo's latest offering has the potential to provide boaters with a low emission, fuel efficient, torquey and long-lasting engine for re-powering existing hulls or as original equipment in new ones.

Published : Wednesday, 1 September 1999

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