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Top 5 Marine Diesel Engines

1) Cummins 6BT 5.9

Cummins 6BT Engine The Cummins 6BT 5.9 is a straight-up, solid, reliable engine. With 25 years’ service in commercial marine applications, it is a popular choice for many, for a variety of reasons. The 6BT can be set up with Keel cooling, Heat Exchanged cooling, dry exhaust, wet exhaust, and an array of PTO options. Many recommend setting the 6BT up with extra heavy-duty transmission with the biggest prop you can fit on your vessel, giving you the ability to economically reach hull-type speeds with the 6BT loading at RPMs between 1500 and 2000 rpm.

However, if you don’t actually need anything near 210 hp, the 6BT can be detuned without too much hassle. Another added benefit that attracts people to this engine, is the fact it can mount a turbo up top. So, if you’re looking for a way to save space then this may be the way to go.

The 6BT boasts a solid engine block more than capable of frequent operation and many working hours. It has a single-cylinder head with four valves per cylinder, so you needn’t worry about its performance ability. As standard, it comes with a Rotary fuel pump, but you can choose to have an electronic governor if precise fuelling is your thing. Other features include a water-cooled exhaust manifold to cut down on emissions, a lubrication system with a 14.2L capacity, and more.


  • Configuration - In-line, 6 cylinder, 4-stroke diesel
  • Aspiration - Turbocharged
  • Displacement - 5.9 L (359 in3)
  • Bore & Stroke - 102 x 120 mm (4.02 x 4.75 in)
  • Fuel System - Inline Injection Pump
  • Length – 1020mm
  • Width – 601mm
  • Height – 1201mm
  • Weight – 426kg


2) Caterpillar C8.7

The C8.7 at first glance looks like a pretty impressive engine, despite only coming in a recreational rating. It has a 2,300lb bobtail, low 2,300 rpm, 641 SAE hp… impressive right? However, many people after a 600-700hp engine would probably be more inclined to go with the Volvo D11. So, what is it that makes this engine worthy of a place on this list?

Well, for starters it sports Cat’s ‘sophisticated’ fuel delivery system that enables the use of a radial, belt-driven supercharger along with a normal turbocharger. Ultimately, this stops all that smoke and reduces lugging. It also makes the C8.7 capable of good low–end torque and an impressive fuel economy. Cat has blended the Fiat Power Train technologies industrial advancement in second-gen common rail fuel injection systems with their air management system, basically allowing the C8.7 to sport an impressive 650 hp at 2300 rpm all while consistent with the provisions asserted in the EPA Tier 3 Commercial, EPA Tier 3 Recreational, IMO II, and EU Stage IIIA (EU IW) emissions standards, what’s not to like?


  • Speed Range - 2300 rpm
  • Stroke - 135 mm
  • Aspiration - TSA
  • Configuration - In-line 6, 4-Stroke-Cycle Diesel
  • Rotation from Flywheel End – Counter-clockwise
  • Displacement - 8.7 l
  • Bore - 117 mm
  • Emissions - EPA Tier 3 Recreational & Commercial, IMO II, EU Stage IIIA (EU IW)
  • Engine Dry Weight (Approximate) - 1041 kg
  • Length - 1218 mm
  • Width - 881 mm
  • Height   984 mm


3) Caterpillar C12.9

Tug Boat Marine Diesel EngineThe C12.9 is a popular choice for high-performance vessels such as yachts, fishing boats, military, and commercial. While a good engine in its own right, it is intended to be integrated with the Cat Three60 Precision Control shaft line maneuvering and engine control solution and various other throttle controls. The C12.9 is electronically controlled, and available in two different power ratings: 850 mph at 2300 rpm and 1000 mph at 2300 rpm. Both of these meet the EPA Tier 3, IMO II, EU Recreational Craft Directive, and EU Stage IIIA regulations.

This engine is a good choice if your after power density, but it is also capable of high torque and low engine speeds, and quick acceleration throughout the whole engine speed range. This is achieved via its air system design of integrated turbochargers and superchargers. The first sign of a good (or terrible) engine is an abundance of videos about it, and luckily for the C12.9, these many videos praise its performance and reliability.


  • Speed Range - 2300 rpm
  • Emissions - EPA Tier 3, IMO II, EU Stage IIIA
  • Aspiration - TA
  • Bore - 135 mm
  • Stroke - 150 mm
  • Displacement - 12.9 l
  • Rotation from Flywheel End – Counter-clockwise
  • Configuration - In-line 6, 4-Stroke-Cycle Diesel
  • Width - Engine  1110 mm
  • Length - Engine 1463 mm
  • Height - Engine 1085 mm


4) Cummins QSB 6.7

The QSB 6.7 has been crowned “bulletproof” by a surprising number of reviewers, and while that may qualify it for a shot at being on this list, what makes it so? The 6.7 boasts a ‘perfectly matched’ turbocharger with a new 24 – valve cylinder head that provides industry-leading power density. An additional benefit is that by using the comprehensive vessel diagnostic information through SmartCraft, you can really exploit the performance of this engine.

Many are equated with 6.7’s predecessor, the QSB 5.9, so that seems like a good reference point. The 6.7 is just as good, with the added benefits of having more mid-range torque, more efficiency, and is overall, significantly quieter, boasting an 80% noise reduction at idle. The cooling system is comprised of a single loop, low temp after cooling meaning better emissions while avoiding the need to have two keel coolers. Another benefit of the 6.7 is that its oil service intervals have been boosted to 500 hours, that is if you are using ULSD fuels.


  • Configuration - In-line, 6-cylinder, 4-stroke diesel
  • Aspiration - Turbocharged / Aftercooled
  • Displacement - 6.7 L (408 in3)
  • Bore & Stroke - 107 X 124 mm (4.21 X 4.88 in)
  • Rotation – Counter-clockwise facing flywheel
  • Fuel System - High Pressure Common Rail


5) Volvo D13-900

Pilot Boat Marine Diesel EngineThe Volvo Penta D13-900 is a versatile diesel engine that is a good all-rounder. It is an inline 6, 12.8-liter diesel engine that utilizes common-rail fuel injection, an overhead camshaft, and a twin-entry turbo via a water-cooled exhaust manifold. The D13-900 is robust and reliable, capable of long action ranges and low emissions. Volvo designed this engine with strength in mind with a rigid cast-iron cylinder block and head to ensure ultimate durability. This engine also has more torque than one could ask for, is capable of high torque at low rpm allows you to quickly get on the plane while offering plenty of maneuvering power.

To save on fuel costs Volvo implemented a high-tech fuel injection system that aids the efficiency of the D13-900. This works by monitoring various parameters to reduce the overall consumption of the engine. Another added benefit is the electronic management system. This is what makes the D13-900 capable of high load carrying. If you are after the impressive performance and an easy-to-maintain engine, this one is definitely worth considering.


  • Rated rpm - 2300
  • Crankshaft Power(kW) - 662
  • Crankshaft Power (HP) - 900
  • Emission compliance - IMO Nox Tier II, EU RCD Stage II, EPA Tier 3
  • Number of Cylinders - 6
  • Aspiration - Dual-stage turbo with twin charge air coolers
  • High-pressure fuel injection - Electronic unit injectors
  • Control system - Electronic Vessel Control
  • Displacement - 12.8

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