MAN V8-900 CRM

A 90 degree V8 version of the MAN R6-800 CRM, the V8-900 has the same cylinder bore and piston stroke dimensions of 128 x 142mm, giving a piston displacement of 14.62lt.

At a time when all other marine diesel manufacturers bar MTU have opted for straight sixes in this power range, MAN has released a compact V8 that develops 887hp at 2300 revs, based on the formula that 1.0hp equals 746 watts. Many components used in the V8-900 are compatible with the R6-800 - such as the individual cylinder heads with four valves per cylinder and the replaceable valve seat guides and valve guides - but sensibly pushrod valve actuation has been retained. Again the compression ratio is a relatively low 15.5:1.

The V8-900 competes with straight-six Detroit Series 60, which develops 825hp at 2300rpm from 14lt and the MTU 8V 2000 M90 which develops 900hp at the same revs. The Series 60 uses unit injectors, a carry-over from the GM two-strokes which pioneered unit injectors, while the 8V 2000 have gone to common rail in line with MAN and Iveco. Unfortunately MTU/Detroit Diesel Allison doesn't provide torque curves or bobtail weights so a direct comparison with the V8-900 is not possible.

Both the V8-900 and 8V 900 are rated light duty for gameboats, fisheries patrol and rescue vessels and subsequently their outputs are conservative compared to intermittent ratings. Light duty allows for up to 1000 hours of operation per year with up to 20 per cent of the time at Wide Open Throttle if the engines reach 2300rpm.

TALKING TORQUE
Whereas the R6-800 produces a peak torque output of 2750Nm at 1200rpm diminishing slightly to 2650 at 2100rmp, the V8-900 produces 2950Nm at 1400rpm down to 2800Nm at 2300rpm. At 1500kg in bobtail form (sans gearbox) the weight is 15 per cent greater for seven per cent more torque and 13 per cent more power, which is surprising considering the V8-900 has a turbocharger per bank of cylinders.

Using standard planing prop power curves, at 1200 revs where the prop absorbs 161hp the fuel flow is 35lt/h compared to 134hp and 25lt/h for the R8-800. At 1600 revs the respective prop power absorption and fuel flow are 349hp/70lt/h compared to 308hp/55lt/h, while at 2000 revs the figures are 630hp/120lt/h and 550hp/105lt/h. At 2100 revs, the maximum continuous output for these engines, the V8-900 prop power and fuel flow figures are 697hp/140lt/h and the R6-800 figures 643hp/120lt/h.

So at 1200 revs the V8-900 produces 20 per cent more usable power for 14 per cent greater fuel flow, at 1600 revs 13 and 27 per cent and at 2000 revs 15 and 14 per cent. At the cruising revs the differences are eight and 17 per cent and at 2300 revs the V8-900 uses 181lt/h compared to 153.6 for the R6-800, a 13 per cent power increase for 18 per cent more fuel. At these revs MAN claims the V8-900 has a maximum lube oil consumption of 600 grams per hour.

The intercooled turbochargers have boost pressure control with a wastegate and the Bosch Common Rail System has a mechanically-operated V-block high-pressure pump driven by the camshaft located between the cylinder banks. The pump supplies fuel to each bank of cylinders via one fuel rail per side.

The fuel rail pressure is maintained at a constant 1600 bar or 22,400psi regardless of engine revs or fuel quantity, ready for each injector firing stroke controlled by the EDC. The rail pressure sensor opens the pressure-limiting fuel return line to maintain a constant 1600 bar and MAN claims that compared to unit injectors common rail allows for both pilot and main injection sequences with no overlap between the two.

As with the R6-800 pilot injection occurs at about 13 degrees BTDC with the main spray at one degree ATDC compared to around five degrees ATDC with unit injectors, which the company claims maintains a constant pressure curve within the combustion chambers for a more thorough air/fuel burn. Yet the design of the injectors is relatively simple compared to unit injectors with the fuel pressure controlling the spray cut-off via the EDC.

Exhaust gas emissions are reduced to the level where the V8-900 complies with US EPA Tier 2 regulations, yet at 560 degrees (slightly below that of the R6-800) the exhaust gas temperature remains relatively cool for a turbo-intercooled diesel.

SHORT BUT WIDE AND TALL
The V8-900's width is substantially more than the R6-800, 1230mm compared to 881 and this means that in twin installations the V8-900 will not suit narrow-beamed performance sportsboats. At 1120mm the height is 143mm more, mainly because of the charge-air cooling between the cylinder banks, but at 1450mm the bobtail length is 155mm shorter.

Like the R6-800 the V8 has a 24V electrical system with 28V, 55A alternator (or up to 120A if required) and a 24V 5.4 kW starter motor. MAN says a 210A/h battery is needed to start the engine and power the EDC.

The V8-900 has been adapted well for marine usage from its trucking origins and electrical components such as the alternator are mounted well above the engine bearers. The lube oil sump capacity of 30lt is the same as the R6-800's but different sump configurations are available to suit the engine operating conditions and mounting height requirements. A paper air filter element is fitted for easy replacement.

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.

The warranty coverage is the same as the R6-800. For more details contact Craig McDonnell at MAN, tel (07) 3271 7777 or email cmcdonnell@manmarine.com.au