Released at this year's Sanctuary Cove International Boat Show, the MTU 6R 1000 and 1800 are direct injection straight sixes that displace 6.48lt and 11.94lt respectively.

Both engines are based on industrial/truck engines and, although they have mechanical fuel injection timing, comply with current IMO standards for NOX (oxides of nitrogen) emissions. According to MTU, the use of truck engines enables the company to provide a comprehensive network of subsidiaries, agencies and service centres for worldwide customer satisfaction and lower spares costs than if the engines were of purely marine origin.

The 6R 1000 has a bore of 103mm and stroke of 129mm and weighs 645kg in bobtail form (minus gearbox). It has a 16:1 compression ratio and standard is a 12V 55amp alternator. It measures 1306mm long, 865mm wide and 965mm high.

The 1000 develops 294kW (394hp at 1.0hp = 746 watts) at 2800rpm for the M91 rating, suitable for planing-hulled cruisers used in recreational applications. This translates to Wide Open Throttle (WOT) 8% of the time in any one operating period and 70% of maximum power 79% of the time. Maximum engine hours per year are limited to 500.

Through the use of MTU's 'Variable Turbine Geometry' for the turbocharger and aftercooler, the 6R 1000 develops 370Nm of torque at just 750rpm, 920Nm at 1350rpm and a massive 1100Nm at 2350rpm. Even at 2800rpm the torque is still 1000Nm!

Fuel consumption is also very reasonable for this engine's output. For example, at 750rpm, where the 1000 can develop 39hp, the usage rate is 8.6lt/hr. Based on a standard propeller power curve, the engine actually develops 15hp and consumes a mere 3.3lt/hr.

At 1350rpm the maximum and actual outputs are 168hp and 47hp and consumption rates 34.6lt/hr and 9.8lt/hr respectively, while at 2350rpm they are 367hp and 235hp and 68.8lt/hr and 43.8lt/hr. The maximum efficiency revs of the 1000 are 2000 where it produces 1060Nm and 295hp and 148hp respectively, while using 53.8lt/hr and 26.9lt/hr. At WOT the 1000 consumes 77.1lt/hr.

The 6R 1000 slots in neatly between Yanmar's straight six 5.8lt 6LY2(M)-STE and 7.4lt 6CX(M)-ETE diesels.

The smaller Yanmar develops a maximum crankshaft output of 309kW (414hp) at 3300rpm, where it consumes 90.2lt/hr. The maximum torque is 1110Nm at 2500rpm where the maximum and prop outputs are 362hp and 221hp and fuel consumption 68.2lt/hr and 41.7lt/hr. This Yanmar weighs 515kg in bobtail form and measures 1274mm x 709mm x 709mm.

The larger model develops 373kW (500hp) at 2900rpm, where it consumes 108.5lt/hr. It produces 1100Nm at 2350rpm and 1000Nm at 2800rpm, but weighs 28% more than the 6R 1000 in bobtail form. This Yanmar measures 1504mm x 869mm x 917mm.

A suitable gearbox for the 6R 1000 is ZF's two speed 110 ATS, which has an 8o down angle at the output flange and weighs 87kg.

The 6R 1800 has a bore of 128mm and stroke of 155mm and weighs 965kg in bobtail form, compared to 1360kg for Volvo Penta's bobtail mechanically-controlled 11.98lt TAMD122A. The 1800 measures 1715mm x 910mm x 1020mm and a 24V 55amp alternator is standard.

The 1800 develops 441kW (591hp) at 2300rpm at an 'M90' rating, comparable to M91. At 800rpm the 1800 produces 820Nm of torque, at 1600rpm 1810Nm and at 2300rpm 1900Nm.

At 800rpm the 1800's maximum and prop outputs are 92hp and 27hp and respective fuel consumptions 18.9lt/hr and 5.5lt/hr. Doubling these revs produces 429hp and 201hp with fuel usages of 74.9lt/hr and 35.1lt/hr. The maximum efficiency revs are 1400rpm where the 1800 produces 1400Nm and develops 268hp and 134hp. The corresponding usage rates are 46.5lt/hr and 23.2lt/hr. At WOT the 6R 1800 consumes 110.4lt/hr.

A suitable gearbox for the M90-rated 1800 is ZF's two speed 312 TS, which is available only with a parallel output flange and weighs 150kg.

The 1800 is also available in M80 and M60 ratings, where it develops 367kW (492hp) at 2100rpm and 294kW (394hp) at 1850rpm, the latter the same output as the TAMD122A but at 50 fewer revs. The M80 rating allows for WOT 15% and 80% of maximum power 85% of the time and is suitable for cruising motoryachts, while the M60 rating is designed for displacement-hulled workboats and heavy displacement sailboats.

The M60 rating slots in between Volvo Penta's Light Duty Commercial and Medium Duty Commercial ratings but the latter allows for four hours of WOT operation in every 12.

MTU has incorporated into each engine a number of clever features to increase engine lifespan. For example, both motors have triple-wall watercooled exhaust manifolds with two separate cooling passages. This system lowers surface temperature on the outside wall, reduces outside heat transfer to the cooling system and creates an absolutely gas-tight manifold.

MTU uses individual cylinder heads of alloy cast iron which simplify regular maintenance and increase component accessibility in confined engine rooms. The cylinder liners are replaceable wet units of centrifugally-cast iron that provide better wear, lower oil consumption and reduce blow-by gas that dilutes the sump oil. This design increases oil change intervals.

The 1800 also has aluminium pistons with cast-in oil cooling galleries, hard-anodised piston crown bowl and ceramic piston ring coatings, giving a high thermal load capacity, reduced piston weight and lower ring wear.

Both models have four-point engine mountings that reduce the transfer of noise and vibration to the engine bearers and provide for adjustable engine mounting height. Both have twin water-separating fuel filters and the 1000 has an inverted oil filter to reduce engine room mess when changing the filter. The 1000 also has a shrouded alternator belt.

MTU's new 6R series is another worthwhile addition to the six and 12lt diesel markets. But with its mechanical injection timing the 1800 may have a hard time competing against its direct electronically-managed Cat and Cummins competition, especially as boatowners I've interviewed are sold on the fuel consumption reduction and throttle-responsiveness of these engines in this power range.

However, there's no doubt the recent merger of MTU-Australia with Detroit Diesel-Allison Australia (part of the Daimler Chrysler Group) should guarantee an excellent level of customer service.

For more information on the MTU 6R 1000 and 1800, contact Steve Anderson, tel (02) 8822 7000 or email: mail@mtu.com.au