Updated Power, Torque, and Fuel Curves, VGT Series



MarineDiesel is always innovating. Always updating our product lines to meet our customers’ needs.

We recently put togather the following document that illustrates the fuel, power, and torque curves in detail for our VGT Series of marine engines.


Some important considerations to note:

  1. In terms of fuel consumption in g/kWh, MarineDiesel’s VGT Series is among the lowest in the market.
  2. Note the flat torque curves of the VGT engines. The VGT Series provides a high, flat torque curve compared to the peaks and valleys so prevalent in competing products.
  3. Note the very gradual power curve. There are no sharp drops, like on competing engines.

These curves prove the superiority of the VGT Series when compared to any other marine engine in the market today. Our VGT Series is specifically designed with the performance requirements that high speed vessel need in order to complete their missions.

Add in the highest power at lowest weight of any other engine in the market, and you have an unbeatable combination of power and performance in the world.

Characteristics of Different Fuels



Different fuels have inherently different combustion characteristics (They burn in different ways and hold different amounts of energy). When considering alternative fuels, it is important to keep these characteristics in mind, over and above merely considering cost of fuel and cost of operation. The chart below demonstrates different fuels and gives an easy “at a glance” comparison between fuel types:

fuel characteristics


Comparison of Auto-Ignition Temperature

The auto-ignition temperature is the temperature at which fuel will ignite without a flame or spark. In respect to the auto-ignition temperatures, LPG, CNG, and LNG are safer than gasoline or diesel.because the auto-ignition temperature is much higher.

Comparison of Peak Flame Temperature

The flammability range is the difference between the leanest (LEL) to the richest (UEL) mixture of fuel and air that will burn. Fuel with narrower ranges are safer to work with, but are less versatile because they offer less choice of air / fuel ratios. CNG has a peak flame temperature of 1,790 deg C / 3,245 deg F, which is 187 deg C / 337 deg F cooler than peak flame temperature of gasoline at 1,977 deg C / 3,591 deg F. The peak flame temperature of LPG at 1,991 deg C / 3,614 deg F is only 13 deg C / 23 deg F (Less than 1%) higher than gasoline.

Comparison of Energy Content

Energy content per unit of fuel (energy density) is an important factor affecting range and power output of internal combustion engines. The higher the energy content of the fuel, the more power the engine will make.

Volumetric Efficiency

The amount of air entering an engine at a particular throttle angle and load is fixed. Any fuel added to the air before it enters the cylinder will displace an equal volume of air and will reduce the volumetric efficiency and power output of the engine. Reductions are as follows:

  • Diesel – Less than 1% (approx.)
  • Gasoline – 1-2% (approx.)
  • LPG – 4% (approx.)
  • CNG – 9% (approx.)

What is LPG?

LPG is “Liquefied Petroleum Gas” Commonly known as propane C3H8, a combustible hydrocarbon based fuel. It comes from the refining of crude oil and natural gas. At normal pressure and temperatures, propane remains in its’ gaseous form. At lower temperatures and / or  higher pressures, propane becomes a liquid.

Propane is odorless and colorless. For safety reasons, propane is required to be odorized. There are currently three grades of propane available: HD5 for internal combustion engines, commercial propane, and propane / butane mixture for other uses. The exact composition of propane varies slightly between different parts of the world and different refineries. Compared to gasoline, the energy content of LPG is 74%.

What is CNG?

CNG is “Compressed Natural Gas”. Natural gas (CH4) is a naturally occurring mixture of combustible hydrocarbon gases found in porous formations beneath the earth’s surface. Natural gas is created by the decomposition of plant and animal remains, under great heat and pressure, over very long periods of time.

Natural gas can be found as:

  • Non-associated gas: Free gas not in contact with significant amounts of crude oil in the reservoir.
  • Associated gas: Free gas in contact with crude oil in the reservoir.
  • Dissolved gas: Gas in solution with crude oil in the reservoir.

For safety reasons, CNG is required to be odorized. Compared to gasoline, the energy content of CNG is 25%.

Industrial LPG Engines



Recently, MarineDiesel has been receiving a number of inquiries about the use of alternative fuels in industrial engines, specifically regarding the use of LPG instead of diesel. Why consider alternative fuels?

Well, there are a number of reasons:

  1. The price of LPG is significantly cheaper than diesel fuel.
  2. LPG is portable.
  3. Cleaner burning with lower emissions.
  4. Lower cost of ownership over the long term.

Are there disadvantages? Of course. There is no such thing as a free lunch. The disadvantages are primarily that LPG produces lower energy than diesel, and in some regions the availability of LPG is not as widespread as diesel.

MarineDiesel manufactures a number of different engines, based on the GM Vortec block, that are manufactured for LPG use.

Initial benefits of the MarineDiesel product line include:

  1. The ability to use LPG instead of gasoline or diesel for power.
  2. Customer payback time in a matter of months through fuel cost savings.
  3. Multiple markets for the engines, ranging in use from small generators to irrigation, mining, marine, pumps, or small vehicle power.
  4. Factory conversion to LPG, as opposed to cheap converter kits commonly found in the market. A primary benefit of this procedure is seamless integration of the LPG kit into the engine’s ECU. Aftermarket conversion kits often do not integrate fully, voiding the warranty or rendering engine fault warnings incorrect. For this reason, aftermarket conversion kits, such as are currently being sold for as much as US$2,000, cannot be recommended for proper installation and life cycle. Furthermore, the Vortec engine blocks have been designed specifically with alternate fuels taken into account. Though there are some immediate cost savings associated with aftermarket conversions, they simply are not an accurate substitution for a proper OEM design.
  5. Full MarineDiesel warranty terms apply.
  6. Swedish government financing may be available.

Here’s an example using the 5.7L Vortec.

5.7 schematic

5.7 table

5.7 kit

Life Cycle

General Motors has been manufacturing the Vortec block configured to LPG for nearly thirty years. Thousands of units have been sold and the engine has proved to be extremely reliable.

The MTBO is at 10,000 hours of use, however, it is highly dependent on climate and continuous RPM.

At the 4,400 annual hours of use described, TBO is roughly every two years.

Cost to Operate

The 5.7L LPG consumes fuel based on engine load.

100% Load:         9.3 m3 / hour

75% Load:            7.1 m3 / hour

50% Load:            5.4 m3 / hour

25% Load:            3.8 m3 / hour




100% Load:         27 L / hour

75% Load:            20 L / hour

50% Load:            12 L / hour

25% Load:            8 L  / hour


Current prices of fuel in SE Asia:

LPG:   US$0.34/ litre

Diesel: US$1.10/ litre

Average annual use of 4,400 hours per year, assuming 75% load at 1,800 RPM.

LPG consumption 3.85 Liters / m3

27.335 Liters LPG / Hour

LPG  annual cost of fuel consumption: US$40,893

Diesel annual fuel consumption: US$96,800




Derating – What does it mean?



Engine buyers are often presented, as a sales pitch, with a lot of gobbledygook about horsepower, torque, how great an engine performs, and so on…

How much is actually true?

With MarineDiesel, you get what you pay for. If you buy 500 hp, you get 500 hp.

Nothing is as frustrating to a vessel operator as receiving a new vessel and finding out that the engines are not producing the power that they thought they had purchased.

Why do these scenarios happen?

It is related to derating.

Engines can be either intentionally derated or unintentionally derated.

Intentional derating occurs when the customer asks the manufacturer to change the engine rating to alter performance or life cycle. There are many reasons why someone would want to do this. Every vessel is designed for a specific purpose and sometimes the vessel’s mission does not neatly fit into a range of standard options or offerings. For instance, if an operator wants a longer service life on the engine, and is willing to accept a reduction in power to receive that service life, the engine can be configured to provide that requirement.

Unintentional derating is a much more troubling scenario. When engines are rated, they are “certified” to provide a certain amount of power and torque for a specific period of time in a specific set of conditions. This is the fine print in the engine brochures and advertising that is usually not very prominent, or is sometimes even missing entirely.

Engines require adequate cooling in order to function properly. If an engine is rated at one level with ambient air temperature of 25 deg. C, using a specific fuel, what would happen if that engine was operating in an environment with an ambient air temperature of 40 deg. C?

The engine will not provide the same amount of power. It must work harder, and the result is a loss.

This is the frustration of the customer. He goes to an engine dealer, is assured of a specific level of power, yet received something else.

This is an area where MarineDiesel shines. Our VGT Series of engines features our own, programmable ECU. We can rate the engines according to climate, use, or customer specifications.

Since the majority of our sales are to military users, who normally must operate in a wide range of temperature extremes, our standard engine ratings assume far harsher conditions than the average customer is likely to experience. If that customer requires something different, it can usually be delivered quickly, and cheaply.

Some specific information about the VGT Series ratings:

Power Standards

The engine performance corresponds to ISO 3046 and a fuel with specific calorific value of 42,7 MJ/kg (18 360 BTU/lb) and a density of 0,84 kg/litre (7.01 lb/US gal, 8.42 lb/Imp gal).

The engines will operate up to 1000 m altitude and 40°C without derating. For operation at higher altitudes the power will be derated according to the following factors:
Altitude derating factor up to 3000 m 4% / 500 m
Altitude derating factor over 3000 m 6% / 500 m
Ambient temperature derating factor* 2% / 5°C
Humidity No derating
*Ambient air temperature at aircleaner inlet


Breaking In a New Engine



MarineDiesel engines are all built by hand, and thoroughly tested before any engine leaves the factory. Our quality control is unsurpassed. Every engine is operated for testing, and is in perfect working order when it is shipped.

However, all diesel engines, when new, require a “Break In” or “Run In” period before being pushed to their limits and operated under extreme conditions. The break in period for the VGT Series is 50 hours. Following this procedure will ensure a long, trouble free engine life.


The Marinediesel VGT series engines need break-in time before being operating to its full potential. This is due to the design characteristics of the base engine.

Follow the recommendations below:

0-5hrs: Use varied load and rpm but do not load the engine above 50% throttle and keep maximum rpm below 2500. Do not stay at one load and rpm configuration for more than 30 minutes at a time.

5-10hrs: Use varied load and rpm but do not load the engine above 60% throttle and keep maximum rpm below 2800. Do not stay at one load and rpm configuration for more than 30 minutes at a time.

Do an oil and filter change after the engine has run a total of 10hrs.

10-30hrs: Use varied load and rpm but do not load the engine above 80% throttle and keep maximum rpm below 3000. Do not stay at one load and rpm configuration for more than 30 minutes at a time.


Act Quick – 2013 Prices Held until May 30



Price increases are a fact of life. MarineDiesel always strives to provide its’ customers the best value possible for their engine needs. We are subject, like any other company, to market forces, and we will soon be revising our price list for 2014.

2013 was a tough year for many shipbuilders, with orders drastically down in many parts of the world.

To help combat this depressed market and give our customers a little breathing room, we will hold to our 2013 price structure through May 30, 2014. Any orders placed before that date, or quotes prepared before that date, will be honored at 2013 prices. Please note this date and submit your orders and quotation requests before that time.

Engine Room Ventilation



MarineDiesel designs its’engines with reliability and service life being key concerns. Using a Duramax block as a foundation for our VGT Series of engines, the product is reliable and trouble-free as long as regular maintenance is performed when due.

There are, however, two situations that can greatly reduce engine life. The first is the use of dirty fuel. The second is inadequate ventilation of the engine compartment.

This situation is most prevalent in tropical, or hot, climates.

All engines produce a tremendous amount of heat. That is how they operate and why they produce power. In order to operate continuously, they must be adequately cooled, with ample ventilation provided for continued operation.

This is where problems can arise. The VGT Series, in particular, being so compact, is often used in very small craft, such as RHIBs, that have very small engine compartments as part of their design. Small, tight, engine compartments tend to lack much ventilation, and therefore ventilation must be provided in order to ensure trouble free operation.

From MDS, our service team:

Engine power is affected by a number of different external factors. Among the most important are air pressure and volume, air temperature and exhaust backpressure. Deviations from the normal values affect engine performance, function and reliability.
Diesel engines require a large amount of air compared to petrol engines. Reductions from the required values show up first of all as an increase in exhaust black smoke. This can be particularly noticeable at the planing threshold when the engine torque demands are high. If the deviations from the required values are great, the engine will lose power. This power loss can
be so great that a planing boat cannot pass through the planing threshold. For the engine to function properly and give full power, it is absolutely essential that both the inlet and outlet air ducts are sufficiently dimensioned and installed correctly.

Two main conditions must be fulfilled.

1. The engine must get enough air (oxygen) to allow efficient combustion.
2. The engine room must be ventilated so that the temperature can be kept down to an acceptable level.

Ventilation is also important to keep the engine’s electrical equipment and fuel system temperature at an acceptable level and for general cooling of engine components.

Basic design.

Engine space ventilation should be considered at an early stage and well before the engine is installed as it is often has to be integrated into the boat structure. Guidelines for air intake area are provided in the installation data and we have provided basic formulae in this section if you wish to calculate your own. Air intake area should never be underspecified, it is always better to have too much than too little. Intake air should always be directed to the bottom of the space and exhausted at the highest part preferably on the opposite diagonal to promote good circulation and natural convection.

There are two schools of thought concerning engine space ventilation, that of the engine manufacturer and that of the boat builder. Most engine manufacturers recommend forcing air into the engine space to provide positive pressure to ensure adequate air supply and ventilation for the engine. Boat builders on the other hand tend to favour extracting air from the engine space to provide a small negative pressure, this can prevent engine odours and fumes entering the passenger compartment through cable and hose ducting, etc.
Either system can be used for MarineDiesel engines but we prefer forcing air into the engine space and having properly sealed engine rooms to prevent odours and fumes. If air is to be drawn out using a fan then we recommend adding the CFM of the fan to that of the engine when working out your air intake area.

Engine room depression.

The maximum engine room depression is 0.5 kPa at full speed, this should be checked in every circumstance irrespective of the type ventilation system used.

Dimension of air intakes and ducts.

The engine itself sucks in air very effectively and naturally will take in air from any direction. Should the inlet or outlet air ducts be under dimensioned, the engine will consequently suck air from both ducts and no ventilation air will go out through the outlet air ducts. This causes dangerously high engine room temperatures and potential engine damage. Most of the radiant heat from the engine must be transported out of the engine room. This is an absolute requirement to keep the engine room temperature below the permitted maximum limit.

Engine room temperature.

Remembering that the engine’s performance figures apply at a test temperature of +25°C, it is important that the inlet air temperature is kept as low as possible. The temperature of the inlet air at the air filters should not be higher than +25 °C for full power output.

There is always a loss of power with increased temperatures and if the engine’s inlet air is constantly above +45°C the engine ECM will de-rate the engine as a safety measure. During sea trials the air temperature in the air filter should not exceed 20 °C above ambient temperature or 45°C maximum.

Location of air ducts.

Air intakes should be located where there is a clean flow of air and away from low pressure zones of the boat structure. They should be designed in such a way as not to allow water ingress into the engine space and provide a dry air supply for the engine(s). Care should be exercised with multiple engine installations to ensure air is delivered effectively to all the engines. If louvers are used, the air inlets should be louvered forward and the air outlets louvered towards the stern, this will encourage ventilation on naturally vented systems. Blowers and/or extractors can also be incorporated if deemed necessary. The channels or ducts for the engine air supply should be routed up as close as possible to the air filters but with a minimum distance of 20–30 cm (8–12″) as a precaution should water enter them.

All channels and ducts must be routed so that the least possible flow resistance is obtained. The bends must not be sharp but softly rounded. The smallest radius should be equal to the internal area. Restrictions must always be avoided.
The ducts should be cut obliquely at the ends to assist flow.


Air intakes or outlet holes must never be installed in the transom. The air in this area is turbulent and usually a mix of water and exhaust fumes and must therefore never be allowed to enter the engine or boat.

Function of air intakes.

Air intakes and outlets must function well even in bad weather and must therefore have efficient water traps. Soundproofing must usually be built in. The air intake and outlet should be placed as far away from each other as possible so that a good
through-flow is obtained. If the intake and outlet are too close, the air can re circulate resulting in poor ventilation.

Engine’s air consumption.

The engine consumes a certain amount of air in the combustion process. This requires a minimum internal area of air supply ducting, the minimum area can be calculated by using this formula.

A = 1.9 × engine power output in Kw
A = Area in cm²

The area of the outlet ventilation ducting can be calculated to be a minimum of a third of the air intake ducting area. The value applies for non-restricted intake and up to 1m (3.3 ft) duct length with only one 90 degree bend. The bending radius should be at least twice the internal area. If longer ducts or more bends are used, the area is corrected by multiplying a coefficient from Table
1 below.

eng vent1

Ambient temperature.

The ambient air temperature, (outdoor air temperature) is assumed to be +30°C (86°F). Correction factors as per Table 2 below should be applied as required by multiplying the calculated area by the correction factor.

eng vent2


A - Air should exit the engine bay and the upper section B – Air should enter the engine bay at the lower section

A – Air should exit the engine bay and the upper section
B – Air should enter the engine bay at the lower section