MAN V12-1550 CRM

MAN has had outstanding success with its four-turbo V12 1500 diesel and the engine is used by a wide range of European boatbuilders such as Fairline and Sunseeker.

Part of the engine's success has been its excellent power-to-weight ratio and flat torque curve, which enables it to power much larger and heavier hulls than would normally be used with twin 1500hp diesels. For example, twin MAN 1500 V12s powered the Sunseeker 75 Yacht tested in Issue 337 of Trade-A-Boat. Although displacing about 43t, this 23.1m hull cruised at 23kt on 1800rpm using 163lt/h per engine and peaked at 33kt on 2350rpm using just over 300lt/h each - not bad for engines having a piston displacement of only 21.93lt.

Unusually in its power range the 1479hp at 2300rpm (at 1.0hp = 746W) 1500 has two intercoolers and a high and low pressure turbocharger per cylinder bank, which allow more torque to be produced at low revs without needing supercharging. Up to medium revs the low pressure turbocharger does about one-third of the compression work and the high pressure stage about two-thirds, but at higher revs and loads a wastegate valve in the bypass between the high and low pressure stage opens, depending on the turbocharger boost pressure. The low pressure stage does about two-thirds of the compression work and the high pressure stage one-third.

The effect of this split in turbocharging is that at low speeds and partial loads the small turbocharger in the high pressure stage works at optimum boost pressure, providing faster planing speeds when the throttle is opened rapidly. At high revs and full load where the exhaust gas pressure is much higher the big or low pressure stage turbocharger provides the density of combustion chamber air needed.

Because all of the exhaust gas energy is used the exhaust temperature is only 501 degrees at the connection flange and 39 degrees lower than the V10-1100 which has one turbocharger per cylinder bank.

Even more torque and a completely flat curve
The result of this split turbocharging is a peak of 4700Nm at 2000rpm with 4000Nm at only 1000rpm and 4300 at 1100. Even at 2300rpm the torque is 4580Nm.

But the common-rail 1550 (which again is a V12 version of the 90-degree V10-1100 and has the same 128mm cylinder bore and 142mm piston stroke) develops 1528hp at the same revs. It produces a peak torque output of 5000Nm from 1200 to 2100rpm, with 4200Nm at 1000rpm and 4400 at 1100. At 2300rpm the output is still 4800Nm, excellent gains considering the bobtail (sans gearbox) weight has risen from 2050kg to 2160kg, achieved by switching to high pressure (1600bar or 22,400psi) common-rail injection.

As mentioned in the reviews of the new MAN R6-800, V8-900 and V10-1100, the Bosch Common Rail system electronically maintains 1600bar in the fuel rails (one per cylinder bank) with the relatively easy to repair injectors delivering two-stage injection for thorough air/fuel mixing and complete combustion. Unlike unit injectors where the fuel spray occurs at about five degrees ATDC, with Bosch CR the first spray is at about 13 degrees BTDC and the main one degree ATDC.

Based on standard prop power curves, at 1000rpm the fuelflow is 40lt/h for both engines, while at 1100rpm it's 50lt/h and at 1300rpm 70lt/h, again the same for both engines. At 1700rpm and a clean plane for most hulls in the 20m range the 1500 uses 125lt/h with the 1550 using 130lt/h, while at 1800rpm the 1550 uses 155lt/h.

Cruising at 2000rpm the 1500 uses 190lt/h and the 1550 uses 205lt/h, while at 2300rpm the fuel flows are 295 and 312lt/h respectively. So for an additional three per cent of maximum light duty output the 1550 uses six per cent more fuel.

As with its less powerful counterparts, the 1550's light duty rating is designed for charter fishing boat operation as well as police, firefighting and rescue boat applications. Light duty allows for up to 1000 hours of operation per year with up to 20 per cent of the time at 2300rpm providing there's no WOT operation below these revs. MAN's light duty rating is more conservative than the direct competition where only eight percent of the yearly time is permitted at rated revs.

Slightly longer and wider but lower
Whereas the 1500 is 2019mm long, 1362mm wide and 1484mm high, the 1550 measures 2025 x 1380 x 1270mm, a reduction in height of 214mm.

As with the V10-1100 the 1550 has individual cylinder heads and four valves per cylinder and the cylinder liners, valve seat inserts and valve guides are replaceable. The electrical system is 24V with a 28V, 55A voltage-regulated alternator standard and a 120A unit optional and at 6.6kW the starter motor is the same as the V10-1100. The engine is well designed for marine usage with electrical components such as the alternator are mounted above the engine bearers, while the twin turbochargers per cylinder bank and intercoolers located between the cylinder banks are surprisingly compact. Twin oil filters are fitted and accessed easily from the starboard side. At 70lt the engine oil sump capacity is the same as the V10-1100.

MAN's Monitoring and Diagnostic System offers analog gauges or digital instrumentation with TFT screens and monitors engine revs and fuel flow, engine and gearbox oil pressure and temperature, engine coolant and exhaust gas temperature and battery output condition. An alarm for any abnormal operating condition is fitted and should any abnormalities occur engine revs are automatically reduced by 25 per cent. A full engine diagnostic facility with memory is standard and the electronic throttle and gearshifting reduce operator effort and eliminate the need for cables, reducing installation time and ongoing maintenance when upper and lower helm stations are fitted.

A two-year full warranty is standard with an option for an additional three years coverage on main components. For more details on the V12-1550 CRM contact Craig McDonnell at MAN Automotive Imports, email cmcdonnell@manmarine.com.au or tel (07) 3271 7777.