Detroit 60 Series

Those who have used early two-stroke GM/Detroit Diesels would be familiar with their throttle-responsiveness and reliability. And also how their distinctive exhaust note separates them from four-stroke diesels!

But times change. With their superchargers and complex machining of transfer ports in the cylinder liners, the two-strokes are expensive to produce. Hence to compete directly with other diesel manufacturers in both OEM and re-power situations, Detroit has released its 12.74lt inline six four-stroke 60-Series engines.

As most diesels in its power range are straight-sixes, Detroit has fallen into line and with its new four-strokes moved away from vee-block engines. And at 130mm bore x 160mm stroke, the 60-Series has the traditional long-stroke diesel design.

Detroit is no stranger to four-strokes. As a naval sea cadet in the early '70s, I learned boat handling on the Australian Navy's 40ft (12.2m) workboats, which were long in the tooth then and powered by four-stroke GM/Detroit Gray Marine diesels. These powerplants developed plenty of torque at low revs, and their ability to stand up to abuse from careless naval training officers and handle heavy tows and loads was legendary.

A few years ago, a friend of mine bought one of these workboats (ex Cockatoo Island Dockyard in Sydney) powered by the original engine and has had no problems.

This time around, Detroit has not taken existing engines and simply modified them to comply with exhaust emission regulations, but designed new models from the engine beds up fitted with four-valve heads and electronic management.

The electronic engine management system allows the engine to idle as slowly as 550rpm, maintain the correct fuel injector timing at all engine revs and under all loads, and allow for throttle/gearshift wires rather than cables to eliminate transmitted vibration to the helmstation(s). The set-up has the usual sensors for low oil pressure, engine overheat and overload indicated by higher than normal exhaust gas temperatures.

The result is a range of compact, fuel-efficient and clean-burning turbocharged and air-to-water intercooled diesels designed to compete directly with offerings from traditional four-stroke companies such as Cat and Cummins.

At present the 60-Series is limited to one model, the 6062 which is rated at 700hp at 2300rpm. More variations will follow.

The engine is rather unconventional (in terms of big diesels) in that it has overhead camshafts, logical for the four-valve heads but still a first when all of the competition have OHV designs with pushrods. The electronic fuel injectors are OEcharged' via rocker arms from the OHC and perform a number of functions.

One is supplying the correct amount of fuel and when as dictated by the Electronic Control Unit. This ensures the engine always gets the right amount of fuel according to revs and load.

Each rocker arm depresses a plunger in each injector. The cavity below the plunger is continuously filled with diesel fuel by the fuel pump and the fuel also cools and lubricates internal components in the injector. A drilled passage connects the cavity below the plunger to a poppet control valve (PCV), located below the solenoid. When the PCV is open, no pressure is created below the plunger and no fuel is injected into the cylinder.

When the PCV is closed, fuel is trapped in the cavity and the downward motion of the plunger pressurises the fuel, resulting in fuel injection. The duration of the PCV being open determines the amount of fuel injected and consequently the engine's power level.

The PCV is responsive enough to open and close twice in milliseconds. And as the PCV's are controlled electronically by the ECU one or more injectors can be turned off as needed.

For example, turning off half the injectors allows the half engine idle feature to function. This quickly warms the engine from cold as three cylinders must do the work of six. Once the engine temperature reaches a pre-determined level the remaining cylinders 'kick in'.

This, according to Detroit, substantially reduces exhaust smoke levels. (We were unable to determine whether the ECU uses the same three cylinders each time).

The new 60-Series ECU displays detailed and descriptive warnings when engine component faults arise and has sufficient intelligence to sense the difference between a disconnected wire and a true problem. At all times the system guards against low coolant level and oil and fuel pressure, high coolant and oil temperature, long or short injector response duration and low or high battery voltage. It also prevents the engine from overrevving in light load situations, such as when the prop breaks clear of the water.

Detroit Diesel also provides an Internet-based troubleshooting facility, enabling owners to sort out any problem should a service technician not be available by using satellite or conventional communications.

The company also provides full training for owners and crew if needed by calling a worldwide service number.

Caterpillar's electronically-managed 12lt straight-six 3196 is the 6062's nearest competition and develops 660 crankshaft horsepower at 2300rpm. In bobtail form (minus gearbox) it weighs 1177kg. Next up the line is the straight-six electronic 3406E, which develops 800hp at 2300rpm, displaces 14.8lt and weighs 1590kg.

Cat Marine claims an average fuel consumption of 28.4lt/hr for the 3196 and 50.6lt/hr for the 3406E.

Detroit's 6062 slots in neatly between the two Cats and as stated above develops 700 crankshaft horsepower (522kW) at 2300rpm and 600hp at only 1720rpm. Allowing for 2.5% gearbox loss, the propshaft output is 676hp at 2300rpm and 600hp at 1760rpm. Unfortunately, Detroit Diesel Allison Australia (DDAA) was unable to supply torque curves and maximum torque figures.

According to graphs supplied by DDAA, at Wide Open Throttle (WOT) the fuel consumption at rated power is 132.6lt/hr, falling to 113.6lt/hr at 1760rpm. But based on an average propeller power curve, at 1760rpm the 6062 consumes a very reasonable 57lt/hr while developing 300hp, while at 1500rpm and 188hp the consumption is 35.9lt/hr and at 1200rpm and 96hp a low 20.7lt/hr.

According to DDAA, Detroit Diesel conducted direct on-the-water trials against Cat Marine's electronically-managed 3406E (800hp at 2300rpm) and found that in a Sea Ray 560 the 6062 was able to reach 2000rpm from 550rpm a full 2.2secs faster than the Cat. When carrying 15 passengers the boat planed from a standing start on only one engine.

During a 50-foot (15.2 metres) 'pass by' test at 2100rpm, the 6062 was 10 dBA quieter than the 3406E under identical conditions. Says Detroit, the 6062 registered at 79 dBA or less than a ringing telephone!

At 41lt the 6062's oil capacity is somewhat larger (better to resist sludging between changes) than the 3196, but less than the much larger-displacement 3406E.

In bobtail form, the Detroit mill measures 1557mm long, 1031mm wide and 1153mm high and has a fairly hefty (for its displacement) dry weight of 1542kg. Compared to the two-stroke 9.05lt Detroit 6V92-TTA DDEC turbo-intercooled diesel, which develops 625hp at 2300rpm, the 6062 is 363mm longer but 138mm narrower and 16mm lower. However, the 6062 weighs 275kg more than its two-stroke counterpart and at WOT consumes 10.8lt/hr more fuel.

The 6062 is a much bulkier and heavier engine than the nearest electronically-managed Cummins competition, the 10.8lt QSM11, which develops 635hp at 2300rpm and weighs 1122kg in bobtail form. It's 264mm longer and 175mm higher but only 53mm wider. This makes it well suited to twin-engine installations and allows for much more of a crawl space between engines than the 6V92-TTA DDEC.

Surprisingly, for its output, the 6062 has a relatively low exhaust temperature of 335?C up to 150?C less than some of the competition. With its thermostatic control, the heat exchanger cooling system maintains a temperature of around 80?C the optimum for a watercooled four-stroke diesel.

The engine is logically laid-out, with the seawater cooling pump and a high-mounted starter motor on the port side and oil fill/dipstick, high-mounted alternator and aircleaner on the starboard side. The management interface module is located atop the gearbox, and the exhaust outlet is directly above the gearbox.

Detroit matches the 6062 with its own single-speed DD6114A hydraulic gearbox which weighs 206kg.

While other manufacturers have taken existing mechanically-injected diesels and made them comply with tough emission regulations by adding electronic management, it's refreshing to see the 'latest' four-stroke manufacturer offering a complete package from the outset.

If the 60-Series is anything like its predecessors, then the opposition had better be prepared for a real stoush!