PATH: BOAT BUILDING & REPAIR » Boat Equipment » Propulsion » Engines » Cummins »

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The Cummins V−555 and VT−555 are 555 cubic inch displacement V8 diesel engines produced by Cummins from 1968±? to 1979±?. It featured overhead valves actuated by rockers, push rods, and roller tappets by a roller camshaft located in the valley of the “V” between cylinder banks, parallel to the horizontal crankshaft. the eight cylinders had “Wet” cylinder liners and direct injection with the injectors being actuated by rockers, push rods, and roller tappets by the camshaft. The engine was available naturally aspirated (V−555) and turbocharged (VT−555).

The turbocharger was fitted to the VT−555 primarily to allow the 555 to develop its Sea Level rated horsepower in the thinner air found at higher altitudes, NOT to increase the overall power rating like most other turbocharged diesel engines as this would overstress the lightly-built internal engine components including the crankshaft bearings and cylinder liners. Therefore, the V−555 naturally aspirated engine and VT−555 turbocharged engine are both rated at the same maximum horsepower at sea level and up to 500 feet altitude. See the Specification Table.

Naturally aspirated engines must be fuel derated 3% for each 1000 feet altitude above 500 feet and 1% for each 10°F (6°C) ambient temperature rise above 85°F (29°C) as warm air is less dense. Turbocharged engines do not require fuel derating below 9,000 feet (2743.2 m) maximum altitude, but above 9,000 feet altitude derate 4% for each 1,000 feet (304.8 m). See the 555 Specification Table, SpecTable Notes, SpecSheet & Shop manual. Note that the Compression Ratio for Naturally Aspirated engines is 17:1 and Turbocharged engines is 16:1.

In an automotive application, fuel derating should be accompanied by a higher gear reduction in the rear end or shifting to a lower gear. In a marine application this is accomplished with a higher gear reduction or less propeller pitch (under-pitching) or both. Vessels operated at sea level benefit little from the standard-boost VT−555 air charging. VT−555 marine engines operated above 500 feet altitude (lakes, rivers, etc.) DO benefit from the standard turbocharger and do not required fuel derating below 9,000 feet (2743.2 m) altitude.

Keep in mind that aftermarket high-boost air charging can overstress this light-built engine resulting in catastrophic engine failure and is therefore, NOT RECOMMENDED.

Click Cummins Engine Company to view
vendor’s profile, contact information, and offerings.

Cummins V & VT Series History

In the late 1960’s, Cummins saw the need for compact diesel engines to power pumps, generators, and farm equipment where load and engine speed were strictly controlled and relatively constant. Small V6 and V8 engines were seen as fitting these applications even though the shortness of the crankshafts forced the connecting rod bearings, crankshaft main bearings and the crankshaft webs to be very narrow and hence very weak which limits the maximum power output of the engine. Never the less, Cummins developed a family of 4⁵/₈” bore 4−stroke cycle V6 and V8 diesel engines of 378, 504 and 555 cubic inch displacement which were designated V−378, V−504 and V−555 respectively for the naturally aspirated models, and VT−378, VT−504 and VT−555 respectively for the turbocharged models.

 The 378 cubic inch and 504 cubic inch engines had a 3³/₄” stroke and the 555 cubic inch engine had a 4¹/₈” stroke, making the engines very much “Oversquare”. The 555 cubic inch engine quickly becoming known as the “Triple-Nickel”.

These engines proved to be barely sufficient when powering pumps, generators, and farm equipment provided they were not lugged, heavily loaded, or quickly accelerated. unfortunately, the fuel crisis of the early 1970’s resulted in these engines, especially the 555, being misfitted to medium duty trucks and school busses where they encountered higher loads, stop and go operation with the need for quick acceleration which quickly revealed their weaknesses. They became known as trouble−plagued engines that experienced catastrophic bearing failures, “thrown rods”, broken crankshafts and leaking liners. In these automotive applications, they also proved disappointingly underpowered. Aftermarket high boost turbocharging simply exacerbated the engine’s weaknesses.

A somewhat less serious problem caused mainly by improper operation was carbon buildout in the combustion chambers that often carbonized the exhaust valves and fouled the fuel injectors, causing a loss of compression, injector misfire, rough running and excessive soot in the exhaust smoke.

A more serious issue was that any lugging or overheating of the engine could quickly damage the “Wet” cylinder liner seals. This would result in engine coolant flooding the crankcase which could cause serious internal damage, including damage to the crankshaft bearings.

The 555 also found its way into marine service where it faired somewhat better, provided it was properly set up with the right gearing and propeller pitch, and then was properly operated. See more about this later in this article under “How to keep the ‘Triple-Nickel’  alive“.

Cummins “Triple-Nickel” Shortcomings

Unfortunately, the 555 suffers from several shortcomings including a “weak bottom end”. Reports of “broken cranks”, “spun bearings” and “thrown rods” NOT caused by “Hydrolocking” are far too frequent. This weakness, however is common of most smaller “V” cylinder configuration engines, especially those with cylinder bores less then 5 inches (127mm) and is due to the overall shortness of the crankshaft. Basically, the smaller the cylinder bore, the shorter the crankshaft, and the weaker the “bottom end”.

Compare the narrow width of a small V8 engine’s connecting rod bearings above with the wider width of an inline 4-cylinder engine’s bearings below which are nearly twice as wide.

With twice as many pistons connected to a V8 crankshaft which is typically only slightly longer then an inline 4-cylinder crankshaft, there just isn’t much room for the connecting rod bearings, the crankshaft main bearings, and the crank webs. Consequently the V8’s bearings and webs must be much narrower as graphically shown in the picture above and the picture below. The red arrow below points to the connecting rod bearing insert ‘shell’ which is highlighted in red.

Obviously, in the case of “slip” type bearings like engine crankshaft bearings, the narrower the bearing, the more difficult it is for the lubricating oil to maintain an oil film between the bearing’s surface and the crankshaft that is adequate to support the heavy loads of a high compression diesel engine as the oil is forced out of a narrow bearing more easily, especially at higher RPM’s. The Detroit Diesel 8.2L crankshaft shown below is from another small V8 diesel engine that is prone to suffer crankshaft bearing failures due to the narrowness of the bearings.

Even though the connecting rod pins on a V8 crank are the widest journals on the crank, when assembled the V8 crank will have two connecting rods crowded onto each rod journal leaving little room for each individual rod bearing.

In the pictures above and the illustration below, it is easy to see how narrow the rod bearings have to be to fit on the short crankshaft of a small V8. Note the two oil feed holes per rod journal (one for each connecting rod. In a fully pressurized lubrication system, the oil is fed to the center of each bearing so that it can form an oil film between the crankshaft journal and the bearing surfaces, as it works its way to the outer edges of the bearing where it squirts out and splatters around the crankcase as the crankshaft turns. Oil tends to exit narrow bearings much more quickly. The wider the bearings, the more oil between the bearing and crankshaft surfaces to carry the load and the more slowly the oil is forced out from between the metal surfaces of the crankshaft and bearings, hence wide bearings can carry higher loads. The larger the cylinder bores, the longer the crankshaft and therefore the more room available for wider bearings. V8 engines with cylinder bores larger then 6″ typically have plenty of room on the longer crankshaft for wide bearings, etc.

Note how narrow the five main bearing journals are and how much larger their diameter when compared to those of the 4-cylinder crankshaft shown in the second picture below. Main bearings will be discussed in more detail a little later.

Another issue with any small V8 crankshaft is the narrow crank webs which are much weaker and consequently much more prone to breakage as shown below.

By comparison, the inline 4-cylinder crankshaft shown directly below, which will have only one rod fitted per journal when assembled, can have much wider rod bearings. And note the much wider main bearing journals which will accommodate much wider main bearings. Also note the wider and much stronger crank webs between the bearing journals.

The inline 4-cylinder crankshaft shown above has 5 main bearings. The crank webs, and the width and diameter of the main and rod bearings have been optimized to carry the stress and load of a high compression, high output engine. By comparison, the V8 crankshaft has the same number of main bearings for twice as many cylinders, and the V8 main bearing journals are much narrower. You can see how crowded a small V8 crankcase can be in the picture directly below. There just isn’t enough room for rod bearings or main bearings to be wide enough to carry the heavy loads generated by a high compression high output engine.

Notice that the main bearing journals of the V8 crankshafts shown in the illustration and pictures above have been increased in diameter to increase the bearing surface in an effort to compensate for their narrowness. But at some point this becomes counter-productive because the increased diameter increases the slip-bearing surface speed which makes it more difficult for the oil to maintain adequate oil film thickness at higher RPM’s. By comparison, a 4-cylinder crank’s main bearings can be wider so they can more easily maintain oil film thickness and carry the loads, hence the journals can be smaller in diameter to reduce bearing surface speed. This is why inline engines with the wider bearings and stronger crank webs, and main bearings between each cylinder can be air charged (e.g. with a turbocharger) to reliably produce more than twice the horsepower per unit of displacement then a small V8. Air-charging these stronger inline diesel engines can also enable them to run cleaner with fewer emissions. This benefit is discussed in detail in our article titled Fuel Fundamentals.

Engines with longer piston strokes have the advantage of being able to produce much higher torque at slower crankshaft speeds (RPMs). Many small V8 engines are designed with a stroke much shorter then most other diesel engines of the same displacement. The 555 is just slightly “over-square” with a 4 ⁵/₈” bore x 4 ¹/₈” stroke. The shorter stroke allows the overall engine height to be lower. Unfortunately, like any of these short stroke, nearly-square and over-square engines, it produce less torque and has to be set-up to run at higher RPM’s to produce its maximum power, which has to be limited due to its increased crankshaft slip-bearing surface speeds, because as bearing surface speed increases, bearing wear increases, and so does the risk of bearing failure.

In conclusion:
The above comparisons show why smaller V8 engines that lack the space for the wider crankshaft bearings and stronger crank webs are not capable of the higher power outputs of comparable displacement inline engines. These are some of the main reasons why most diesel engine manufacturers have abandoned building small V8 engines and have embraced inline configurations especially the turbocharged 6 cylinder inline with 7 main bearings such as the Cummins B and C series engines. In the case of V8 engines with bores larger than 5 inches (127mm), the engine’s overall length is longer allowing the crankshaft to be longer, and therefore have more room for wider crankshaft bearings and stronger crank webs which means that they can have much stronger “bottom ends” and therefore higher power outputs  per displacement unit then their smaller, shorter, and weaker little brothers.

An additional issue with the 555 is that, any “liner shake” caused by lugging of the engine can quickly cause damage to the “Wet” cylinder liners and seals, and head gaskets that often results in engine coolant flooding the crankcase.

Another issue concerns quality replacement parts which are becoming scarce and more expensive. New major parts (i.e. blocks, heads, crankshafts, etc.) are practically non-existent and usable used parts are also becoming more scarce as more “take-outs” are simply scrapped.

How to keep the “Triple Nickel”  alive

Because of these recognized inherent weaknesses, Cummins never did set up the 555 engines to produce very high power outputs especially when compared with the inline engines like the B and the C series engines. The V−555 (naturally aspirated) must be fuel derated above 500 feet altitude and the VT−555 (turbocharged) must be fuel derated above 9,000 feet altitude (See the Specification Table, SpecTable Notes, SpecSheet & Cummins Shop manual). Fuel derating should be accompanied by a gear reduction and In a marine application this includes a gear reduction and/or under-pitching the propeller.

When operating the 555, rapid acceleration or lugging (such as when towing another vessel or single engine operation of a twin engine vessel) should be avoided as this causes excessive internal stresses and over-fueling, even at slower RPMs. In such cases, a higher gear reduction and/or lower pitch propeller is advised.

If the 555 engine is intentionally operated at reduced power (below 80% of full power), by shifting down and easing up on the throttle, doing so has proven to help it survive. In a marine application this can be accomplished by higher gear reduction and/or under-pitching the propeller, which will stress the engine less, but will reduce the vessel’s cruising speed.

Unfortunately, running the engine at any slower RPMs and/or lower loads will lower combustion gas temperatures (below 800ºF) that encourages excessive soot with carbon buildup (carbonization) and its ensuing problems, including “injector misfire” and detonation. Since the practice of routinely running at full throttle (flank speed) and load to blow out the carbon soot is NOT recommended with the 555, because doing so risks catastrophic bearing failure, other ways of reducing carbon buildup must be utilized. Adding fuel additives that help keep fuel injectors clean and reduce carbon buildup can be quite useful.

Like many 4-Stroke Cycle engines, the 555 will tend to detonate when started in colder weather. Detonation is the phenomenon that occurs when the heated gases from combustion expand in the combustion chamber faster then the speed of sound and generate a supersonic shockwave. Detonation in a cold engine is the result of the increased ignition lag-time that unfortunately, delays ignition until the combustion chamber has an overabundance of fuel. Once ignited, the large quantity of fuel burns too fast, generating a shockwave. This shockwave or “sonic boom” if you like, can be heard by the naked ear as the characteristic “knock” or “ping” of detonation depending on the frequency of the sound, the “ping” being the higher frequency. Typically, the larger the cylinder, the lower the frequency. When detonation occurs in the 555, which mechanically injects the diesel fuel directly into the relatively fragile cylinder instead of into a heavily reinforced precombustion chamber, the shockwave too often causes damage to the  head gaskets because they are directly exposed to the shockwave. Starting any diesel engine in cold temperatures is greatly improved by fitting an engine warming device such as a block heater or an intake air heater. Heating the incoming air reduces the ignition lag-time, avoiding detonation. Starting and running this engine in the summer with winter blend diesel which contains additives to improve starting in cold temperatures, can also cause internal damage from detonation and should therefore be avoided.

It is never a good idea to use “Ether” to start a 555 as it will often detonate in the cylinders causing head gasket damage or worse. Of course having such a volatile fuel as starting fluid in the engine space of a vessel, especially a diesel fueled one, is extremely dangerous. Why are volatile fuels such as starting fluid, gasoline or propane so dangerous in diesel powered vessels? Well remember that electrical devices such as relays, generators, alternators and starter motors on diesel engines in most vessels are not required to be ignition protected and therefore can provide an ignition source such as a spark resulting in an explosion and fire. Also, a diesel engine can “run away” on a volatile fuel in the engine space. So instead of using starting fluid, if the temperature is too cold for the engine to start easily, it is better to fit an engine warming device such as a block heater which is usually AC powered or an intake air heater which is usually DC and can be powered by the ship’s batteries.

Next, pay particular attention to the engine’s cooling system, especially the raw water pickup and sea strainer. Keep them clear of any obstructions. Also keep the raw water pump impeller, the heat exchanger, the engine coolant (antifreeze), the pressure cap, all hoses, and the engine belts and pulleys in good shape. The exhaust mixing elbows on wet exhaust systems should be routinely checked for deterioration and clogging. Even the slightest overheating can result in leakage of the wet cylinder liner seals as mentioned before. Make sure that an audible and visual (horn & light) engine overheat alarm is installed and operational and never continue to run the engine once the engine overheat alarm has sounded. Engines with wet exhaust systems would benefit from installation of exhaust system overheat alarms which give earlier warning when the raw water cooling supply is interrupted.

Fluid analysis of the engine coolant and engine oil can help detect deterioration and contamination of the fluids and can also help determine the extent of other internal damage.

It may also prove helpful to pull the fuel injectors and inspect the cylinders with a borescope for carbonization.

Ensure that the engine oil is properly maintained. Always use a quality Diesel Engine Lubricating Oil such as DELO 400 which still has a substantial amount of Zinc. DO NOT USE DELO 100 as it is a low detergent oil intended for Detroit Diesel’s 2-Stroke Cycle engines. See our webpage on engine oil. Always shake or stir the new oil container to mix the new oil before pouring the new oil into the engine as the oil and additives tend to separate over time. This is especially true of larger containers of oil such as drums which must be stirred routinely to mix the heavier additives like zinc that have settled to the bottom of the drum. Always maintain the proper oil level in the engine. Always replace the oil filter during every oil change. Then cut open the old filter and check it for metal. See our webpage on Inspecting Oil Filters for metal. Always use a quality oil filter. Consider fitting the engine with a by-pass oil filter in addition to the original full-flow oil filter. See our Article on Installing a Bypass Oil Filter. The small micron by-pass filter’s element can remove much smaller contaminate particles from the oil then the larger micron full-flow filter’s element can, thus reducing wear from oil contaminates. The V−555’s narrow crankshaft bearings make them more susceptible to wear from these smaller particles contaminating the oil when the oil film between the bearing and crankshaft is pressed thin.

Lastly, let’s consider one more source of wear and failure. If the engine sits dormant for long periods, consider fitting a pre-oiler to the engine to pressurize the oil galleys and fill the bearings before starting the engine. This practice reduces wear during startup, which is considerable especially in the case of the narrow V−555 crankshaft bearings. Pre-oilers are often fitted to commercial engines to reduce startup wear. See our webpage on Engine Pre-Oilers.

A surprising number of vessels were fitted with 555s for propulsion due to their rather reasonable original price. Unfortunately, due to the 555’s shortcomings, many of these engines are in trouble. Some of the owners aren’t aware of any problems, but again some are. There is no denying that the 555’s problems haven’t adversely effected the value of the vessels which are equipped with them. Whether you own such a vessel already or are considering buying one, a good place to start is with a fluid analysis of a properly drawn engine oil sample. Even when you don’t have any previous sampling results to trend from, The analysis of a single current sample can still reveal if any of the shortcomings inherent in the 555 have already resulted in damage to the engine and to just what extent. Academy members have the opportunity to submit oil analysis reports to our engine experts (at no charge) for their opinions and suggestions as part of our “Ask An Expert” Program.

If the 555 is currently in good condition, and your plan is to keep the engine for awhile, the best advise is to make the above improvements, keep it maintained, and run it easy. If you intend on keeping the vessel for a while, you should probably start budgeting for a repower. But remember that tight quarters may limit your choice of replacement engines. The Cummins B Series diesel engines have proven to be an excellent replacement if it will fit.

Similar engines produced by other manufacturers

During the 1970’s fuel crisis, Detroit Diesel saw the need for a cheap, fuel efficient engine to power medium trucks and school busses. Their answer was a lightweight, slightly under-square (108mm bore x 112mm stroke) 500 cubic inch displacement, four-stroke-cycle V8 diesel engine designated the 8.2 Liter and called the “Fuel Pincher“. The engine was eventually marinized by a few third-party companies (¿including Johnson & Towers?) and fitted to vessels, but they proved to be quite troublesome as they were prone to “blowing” head gaskets due to the “free-standing” cylinder design and lack of a proper “deck” to support the head, and also bearing failures due to its weak “bottom end”.

Caterpillar had came out with the 1100 medium truck engine in the 1960’s which became the 3160 marine engine. It was a larger bore V8 engine at 636 cubic inches of displacement, so it did not suffer as much from a weak “bottom end” as it’s smaller V8 rivals. However, in marine use, it sometimes suffered from a design flaw of the camshaft driven gear that resulted in the gear spinning on the camshaft during a “hard shift” or a “prop-strike” causing catastrophic internal damage to the engine. When Caterpillar came out with the 3208 (the 3160’s successor), they improved the strength of the “bottom end” slightly, but did nothing about the camshaft gear flaw. Installation of a “Drive Saver” propshaft coupling would be a wise investment as it could save the engine from such damage.

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Specifications For Cummins “V” Series
4−Stoke Cycle V6 & V8 Diesel Engines
Features: Horizontal Crankshaft and “V” Pattern Wet Liner Cylinders

TABLE KEY:
Types of Engine Vendors: Engine design owners may produce the engines in-house as manufacturers.
^ Licensees are licensed by engine design owners to produce base engines and/or marine engines.
^ Marinizers buy base engines from the producers at wholesale, marinize them for marine service,
^ ^ and then sell them to boat builders, resellers, etc. at wholesale or to end users at retail.
^ Resellers buy marine engines at wholesale and resell them at a markup or at retail.
BASE ENGINE: Manufacturer/Vendor & Model of Base Engine followed by Specifications.
^ CYL: Cylinder Orientation & Configuration – (Dash w/no spaces) Number of Cylinders: (example: “V-8”)
^ ^ Cylinder Orientation: No Code = u… = Upright (Vertical).
^ ^ Cylinder Configuration: …V = V Pattern (eg V-8).
^ BORE & STROKE: …mm = Millimeters. …in = …” = Inches.
^ DISPLACEMENT = Swept Volume: …cc = Cubic Centimeters (cm³). …L = Liters. …ci = Cubic Inches (in³).
MODEL RATINGS: Base Engine Model, Vendor Rating Code, Duty Ratings, Power Ratings, etc.
^ A-F: Aspiration-Fueling: Intake Air uncharged or charged – Petrol or Diesel Fueling.
^ ^ Aspiration: N = Naturally Aspirated. T = Turbocharged. …i = Intercooled. …a = Aftercooled.
^ ^ Diesel Fueling: M = Mechanical Injection. …ii = II = Integral Injector. …d = Direct Injection
^ DR = Duty Ratings: See the Engine Duty Ratings Description at the end of the Table.
^ ^ ♦♦ = Highest Power Rating from Data Sources.
^ POWER: kW = Kilowatts. HP = Horsepower. BHP = Brake Horsepower. SHP = SAE Horsepower.
^ RPM = Power Ratings @ Revolutions Per Minute.
^ YEARS: Beginning-Ending. Trailing “–” (Dash) without an Ending Date = Still in Production/Available.
^ ^ YYYY usually = Model Year. MM/YY = actual Month/Year.
^ ^ Vendors typically market products after production ceases, often until stockpiles are exhausted.
^ DS = Data Source: Click DS Link to view DS. ♦♦♦ = Summary of Data Compiled from Multiple Sources.
^ ^ DS’s 1st Letter = Vendor’s 1st Letter (example: F = Ford). Wik = Wikipedia. BD = BoatDiesel.com.
^ ^ DS’s 2nd Letter:  …d = Directory. …w = Webpage. …c = Catalog. …b = Brochure. …s = SpecSheet.
^ ^ ^ …o = Owner’s/Operator’s Manual. …m = Service/Repair/Technical/Workshop/Shop Manual.
^ ^ ^ …p = Parts Catalog. …# = Serial # List …h = History. …y = Years Vended (History). …f = Forum.
^ ^ DS’s Last Digits: …1,2,3,A,B,C,etc = Source #, Version, Revision (example: Fc1 = Ford Catalog #1).
Data: ⊗ = Data Not Available from Data Source. ¿… = …? = Data Unconfirmed/in Question.

Clicking a Vendor Link in the table will open a new window displaying our webpage for that Vendor containing details about that vendor and their products. Clicking a Model Link in the table will open a new window displaying our webpage for that Model.

HOW TO READ THIS TABLE

Each line displays the data available from the identified Data Source (DS). The data is displayed according to the Table Key above. Clicking on the Data Source Link will open a new window displaying that Data Source. Data Sources include Catalogs, Brochures, Ads, SpecSheets, Owners/OpManuals, Parts Catalogs, Shop Manuals and Articles. The Triple Diamond "♦♦♦" = Summary of data compiled from multiple Data Sources.

Keep in mind that Data can be inaccurate in the source material and sometimes, the source material may be illegible. We try to obtain the best source material available and we make corrections to the tables when needed. If you wish to point out an error or you can help us obtain good source materials, please let us know via email To: Editor♣EverythingAboutBoats.org (Replace "♣" with "@")

NOTES: The turbocharger is fitted primarily to allow the engine to develop its Sea Level rated horsepower in the thinner air at higher altitudes up to 9,000 feet. Naturally aspirated engines and turbocharged engines are rated at the same maximum rated horsepower at up to 500 feet altitude. Naturally aspirated engines must be derated 3% for each 1000 feet altitude above 500 feet and 1% for each 10°F (6°C) ambient temperature rise above 85°F (29°C). Turbocharged engines do not require fuel derating below 9,000 feet (2743.2 m) maximum altitude, above maximum altitude derate 4% for each 1,000 feet (304.8 m). Compression Ratio for Naturally Aspirated engines is 17.0:1 and Turbocharged engines is 16.0:1. See the SpecSheet & Cummins Shop manual.

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Cummins
Engine Duty Ratings

Agricultural:
C = Continuous: Power available continuously.
I = Intermittent: Power available for 1 hour out of 8 hours with low annual hours.

Automotive:
C = Continuous: Power available continuously.
I = Intermittent: Power available for 1 hour out of 8 hours with low annual hours.

Industrial:
C = Continuous: Power available continuously.
I = Intermittent: Power available for 1 hour out of 8 hours with low annual hours.

Marine:
C = Continuous: Power available continuously.
I = Intermittent: Power available for 1 hour out of 8 hours with low annual hours.

Power Generation:
GC = Generator – Continuous.
GP = Generator – Intermittent Peak Load.
NOTES: AC Generators usually turn 1500 RPM for 50 Cycle and 1800 RPM for 60 Cycle.