Review: Nanni Diesel N4.60

By: Andrew Norton

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  • Trade-A-Boat

The Nanni Diesel N4.60 is the smallest turbo-diesel marine engine in its Kubota range.

Review: Nanni Diesel N4.60
The Nanni Diesel N4.60 is ideal for lightweight performance keelboats and semi-planing cruiser hulls.

I’m not really a fan of straight turbo-diesel engines in boats. It’s sort of like a halfway measure between naturally aspirated and turbo-intercooled engines.

But for some hulls straight turbo-diesel engines do make sense. Lightweight performance keelboats and semi-planing cruisers come to mind. The additional torque and power over naturally aspirated engines without incurring much of a weight penalty, can be an advantage.

The Nanni Diesel N4.60 is one such marine engine. Not only does it develop significantly more torque than its 2.2lt naturally aspirated Nanni Diesel N4.50 running mate but maximum torque is carried higher up the rpm range, useful for getting a semi-planing hull out of the hole. Of course it would only suit such a hull to around 5.5m, too small for even the Arvor 20.

The real forte of this engine is powering lightweight keelboats to 14.5m and/or 11 tonnes. Correctly propped the waterline length of these should allow a maximum speed of around 9kts with an 8kt cruise, keeping load on the engine but not over-stressing it.

 

NANNI DIESEL N4.60

As with all of Nanni Diesel’s smaller Kubota-based diesels the N4.60 has indirect injection intended to meet all current recreational marine engine exhaust emission requirements.

The engine has the same piston stroke as the Nanni Diesel N4.50 but a narrower cylinder bore to allow more air into the combustion chamber. But because the turbo boost is only 0.55 to 0.6 bar (8 to 9psi) the N4.60 remains way under-stressed compared to some of its same-displacement straight turbo competition and has an exhaust gas temperature range of only 450 to 500°C, not much higher than naturally aspirated diesel engines of similar output. This is helped by a seawater pump flow of up to 100lt/h compared to 70 for the N4.50.

The compression ratio is 21:1, with no provision for hand starting, just as well as only professional wrestlers would be able to crank over this engine by hand.

Of course the Nanni Diesel N4.60 has all the traditional Kubota tractor engine features, such as cast iron cylinder block and head plus gear driven pushrods to operate the overhead valves. One of the competitor’s engines in this power range has a belt-driven OHC design, just something more to go wrong at sea!

The raw or sea water cooling pump is driven from the camshaft, while the freshwater pump is powered by the same V-belt as the high-mounted voltage regulated 100amp alternator. Nanni Diesel doesn’t fit a shroud over the V-belt, obviously reasoning that who would be stupid enough to stick their fingers into a rapidly moving belt. That’s French logic for you!

Thank heavens the standard instrument panel has an analogue tacho that reads to only 4000rpm, so you can see more precisely how your engine is performing. Cleverly the digital hour-meter is incorporated in the tacho, flanked by oil pressure and engine coolant temperature gauges. There are also warning lights for glow plug preheating, water in the fuel filter and low battery charge.

 

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Nanni Diesel offers a wide range of transmissions, including the Italian Technodrive SP60 saildrive which unfortunately has a dog clutch. Good thing the N4.60 idles at only 800rpm in gear, so there won’t be too much of a clunk when engaging ahead or astern gear. On its fibreglass mounting bed the saildrive N4.60 is 1144mm long, 594mm wide and 796mm high.

Shaftdrive gearbox choices range from the mechanical ZF25M to the hydraulic TM345A box with eight-degree down angle at the output flange. My advice is that if you’re repowering a yacht opt for a mechanical box as your prop can freewheel under sail, unless a folding prop that can be locked in position is fitted. Hydraulic boxes don’t like running without lubrication. With the standard ZF box the shaftdrive model is 937mm long, 505mm wide and 632mm high, about the same as the N4.50!

To handle the oil loads from the turbocharger, depending on installation angle the lubricating oil sump holds up to 10lt compared to 7.5lt for the N4.50. The sump drain plug is at the forward end of the engine, so removing all the old oil may be a challenge. Nanni Diesel recommends SAE 15W40 diesel oil and along with the filter this should be changed every 100 hours or six months. Turbos don’t like dirty oil.

 

THE TRADE-A-BOAT VERDICT

With its under-stressed powerhead the N4.60 should provide years of reliable motoring. The turbo boost is not as high as some of the direct competition and the relatively simple engine design ensures less to fail at sea. And Nanni Diesel has an excellent dealer representation, so if there is a problem it should be quickly fixed.

Visit nannidiesel.com.au for more information.

 

NANNI DIESEL N4.60 ENGINE PERFORMANCE

Maintaining engine load is more important with a turbocharged diesel than a naturally aspirated unit. Running a mechanically-injected engine, such as this one, at too low rpm for long periods will glaze the cylinder bores due to fuel over-supply. So the N4.60 needs to be worked and is not an engine for pottering up rivers.

RPM

MAX TORQUE (NM)

BHP (ABSORBED BY PROP)

FUEL BRUN (LT/H)

1200

164

2

1.5

1400

165

4

2.1

1600

166

8

3.1

1800*

168

11

4.2

2000

168

18

5.2

2200

165

25

6.5

2400

160

34

8

2600*

155

45

10

2800

151

59.2

12.2

* My minimum and absolute maximum continuous cruising rpm. In head seas the maximum rpm should be 2400. To keep Europeans happy, the maximum output is 44.2kW, translating to 60.1 metric horsepower. For oldies like me this is 59.2 brake horsepower. –Performance data supplied by the author.

 

NANNI DIESEL N4.60 SPECIFICATIONS

TYPE Four-cylinder turbocharged diesel

RATED BHP 59.2 at 2800rpm

MAX TORQUE 168Nm at 1800 to 2000rpm

DISPLACEMENT 1999cc

BORE X STROKE 83 x 92.4mm

WEIGHT 248kg (dry w/ hydraulic gearbox); 270kg (dry w/ SP60 saildrive)

 

See the full version of this review in Trade-A-Boat #464, April / May 2015. Why not subscribe today?

 


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