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Eight considerations when choosing an engine, other than horsepower

 

 

There are two determinants that are primary in many engine buyer’s minds when choosing an engine: Horsepower and price. However, there are other factors, sometimes more important, that need to be taken into account when choosing an engine:

  1. Torque. Torque is often neglected in terms of considerations instead of horsepower, but it can actually be more important. This article from earlier this year explains the reasons why consideration of torque is so important.
  2. Fuel consumption. A difference in fuel consumption rates of only a few grams per kilowatthour equates to thousands of Euros per year in additional operating costs.
  3. Space. Engines must be able to fit into the space available.
  4. Weight. Heavier engines require more power to move. On boats, extra weight translates directly into extra displacement.
  5. Noise. This especially applies to gensets, but also on propulsion engines. Noise can become highly problematic in some applications.
  6. Life Cycle. Small differences in life cycle translate into thousands of Euros in additional costs over the life of the engine.
  7. Cost of spares. All spares are not created equally. Some brands have a reputation of having a high cost of spares.
  8. Maintenance network. Dealers and local service are important. That few thousand Euros saved at purchase is easily eaten up by additional downtime costs. Waiting weeks for spares to arrive from China gets very expensive, very quickly.

 

VGT Series vs Volvo Penta D-Series – How do we compare?

 

 

The VGT Series of marine engines is MarineDiesel’s flagship product. We originally aimed to make the lightest, most powerful, most reliable engine available in the market, and we succeeded where others have not.

So, how does the VGT Series compare to others?

Price:

MarineDiesel VGT: Mid-range

Volvo Penta D-Series: Expensive

*Price will vary greatly based on many factors, including import duties and dealer markups, but in general

 

Cost of Spares:

MarineDiesel VGT: Mid-range

Volvo Penta D-Series: Very Expensive

*Note: The Volvo Penta engines require special diagnostics tools for maintenance.

 

Rating:

MarineDiesel VGT: Commercial / Military Medium to Heavy use

Volvo Penta D-Series: Recreational

 

Engine Block:

MarineDiesel VGT: V-8

Volvo Penta D-Series: Inline 6

*Inline cylinder arrangements tend to produce higher levels of vibration

 

Weight:

MarineDiesel VGT: 500 kg

Volvo Penta D-6: 785 kg

 

Fuel Consumption:

MarineDiesel VGT: Max 220 g / kWh

Volvo Penta D-6: Max 225 g/kWh

 

Curves:

vgt400 curves

MD VGT 400 Power and Torque Curves

vgt400 fuel

MD VGT400 Fuel Curve

d6400 curves

Volvo Penta D6-400 Power, Torque, and Fuel Curves

 

 

 

 

 

 

 

What is torque?

 

 

Webster’s defines torque as:  a force that produces or tends to produce rotation or torsion <an automobile engine delivers torque to the drive shaft>; also:  a measure of the effectiveness of such a force that consists of the product of the force and the perpendicular distance from the line of action of the force to the axis of rotation.

Engine makers often highlight the amount of torque their engines provide. Why?

Since torque measures rotational force, and internal combustion engines produce rotational force via a camshaft, torque measures how much force is actually generated through the flywheel, rather than the force of the pistons in the cylinder.

Quite simply, torque is often a far more useful measurement or indicator of an engine’s performance. In other words, it can be easier to explain thusly: Whereas horsepower measures power, torque measures the amount of work that an engine can perform.

Torque is measured in Newton Meters, Nm, and is determined via testing on a dynamometer.

Diesel engines produce usable torque only at a limited range of rotational speeds. The amount of torque produced at any one point on the curve can vary significantly between one engine and another. This is why torque is more useful to engine buyers than merely horsepower. Torque measures the work an engine can perform.

To illustrate, take two 500 hp engines, one mounted on a small tugboat, and one mounted on a racing boat. Both engines produce 500 hp, but the tugboat needs far more torque in order to pull a heavy load, at far slower speed than the racing boat that needs a rapid accelleration and maintaining a high speed.

This is why careful examination of the torque curves is critical when choosing an engine. All power is not created equal.