EARLY STEPS

It was not until after World War I that the internal combustion engine had reached a sufficient degree of development, reliability and performance that the New South Wales Government Railways (NSWGR) began to seriously look at this technology as a solution for branch line rail vehicles. A number of States had earlier experimented with various types of light rail vehicles but none of these proved completely successful. The first NSW move was the conversion of a derelict Moreland truck in 1919 into Rail Motor No.1. This vehicle was powered by a 42 hp 4-cylinder American Waukesha petrol engine. This engine was later replaced by a 40 hp British Thornycroft 4-cylinder petrol engine. This vehicle proved a success on the then isolated Grafton to Casino line.

The drawback with Rail Motor No.1 was that it was only single ended and needed to be turned at the terminus for the return journey. Therefore double-ended operation was to be provided in the next prototype vehicle, Rail Motor No.2, built in 1921. The only reliable form of double-ended operation then in general use was the heavy petrol-electric method of traction. So as to reduce weight, NSWGR decided to use mechanical means to overcome the reversing problem. The solution was achieved by manufacturing a 100 hp reversible 6-cylinder petrol engine at Eveleigh Workshops. This was a remarkable piece of engineering for its day and reversing was achieved by having two sets of camshafts (one for each direction) that were selected by pneumatic operation. This engine was fitted to a suburban end-platform passenger car and drove through a 3-speed gearbox to a worm driven final drive on one bogie with both axles driven. When Rail Motor No.2 was withdrawn from service, the engine was removed and sent to Armidale where it was used as a stationary pump engine.

PRODUCTION VEHICLES

Following on from the experience gained with the two experimental types, a new standard production vehicle was designed and built by NSWGR Eveleigh Workshops, the first unit (No.3) entering service in December 1923. These vehicles became the ubiquitous 42-Foot Rail Motors. For these production vehicles, NSWGR reverted to commercially manufactured engines and the initial batch of vehicles was fitted with a British-made 72 hp 6-cylinder Thornycroft Z6 petrol engine coupled to a Thornycroft 4-speed manual gearbox driving by a cardan shaft to a reversing final drive located on the inner axle of the driving bogie. The Z6 engine proved to be unreliable and NSWGR records indicate a number were replaced free of charge by the manufacturer. Later vehicles were fitted with a more powerful 100 hp 6-cylinder Leyland engine. This 927 cubic inch (15.3 litre) engine providing the necessary power and reliability required and the entire class of 37 were eventually fitted with this engine.

Following the success of the 42-Foot type with the public, the next step was to produce a larger vehicle to meet growing passenger demands. This move would have required a significant increase in the size and weight of the vehicle if a single engine of sufficient performance was used and the higher operating costs involved would negate all of the obvious advantages of the rail motor type vehicle. The answer came in the form of a new Leyland Model E47/1 150 hp 6-cylinder engine coupled with a Lysholm-Smith torque converter transmission. This 611 cubic inch (10 litre) engine was lighter than the earlier 15 litre type and the torque converter transmission enabled a twin-engine installation to be designed. The resulting vehicle was the 55-foot Rail Motor No.38 appearing in 1934. No.38 was essentially an enlarged version of the 42-Foot type and a companion trailer, No.81, was also constructed to work with the power car. This engine and transmission was also later deployed across a number of 42-Foot Rail Motors.

The Rail Buses of the late 1930's were built on a commercial truck chassis and were powered by a 31 hp V8 Ford Mercury petrol engine with a manual transmission. Some of the Mercury engines were later replaced by V8 Ford Thames engines.

The NSW Railways followed the national trend of the time by looking to the Great Britain for the provision of motive power solutions. While Rail Motor No.1 was initially fitted with an American Waukesha engine, this was probably the original truck engine and when this was worn out it was replaced with a British-made Thornycroft unit. Further reliance on Britain followed with Thornycroft, Leyland and AEC petrol engines and Harland and Wolff, National and Leyland diesel engines being used in the various classes. The first departure from this practice was the trial of US-made Winton engines in CPH 25 and CPH 30 from 1933.

Click here for more information about petrol engines

Gas producers were fitted to a number of the CPH Class units during World War II to reduce petrol consumption which was then being rationed domestically due to wartime shortages. It is interesting to note that five of the six units fitted with gas producers were destroyed by fire.

THE FIRST DIESELS

In the 1930's, many European and American railways were pursuing lightweight high-speed diesel trains and NSWGR followed suit with a similar train to provide main line services on the Broken Hill line in 1937. The Silver City Comet, as the train became known, consisted of a locomotive, called a 100 Class Power Van, and a number of passenger trailers. The power van was of all-steel construction and was powered by two British-made Harland and Wolff "Harlandic" 330 hp 8-cylinder 2-stroke diesel engines driving through Voith-Sinclair hydraulic transmissions. The engines were built under licence from Danish shipbuilding company, Burmeister and Wain, by Harland and Wolff at their Belfast, Northern Ireland works. These engines were not as powerful as required for a fully loaded Comet set and a multi-valve cylinder head was designed but was not supplied from Belfast until 1943 due to production difficulties during World War II. Two smaller National 32-hp 4-cylinder diesel engines were also fitted to generate power for the air-conditioning and to drive auxiliaries.

In parallel with the Comet development, a smaller branch line rail motor was also designed and built by Eveleigh Workshops, the first entering service in 1938. The 400 Class were of composite steel and timber construction and were fitted with a repeat of the twin 150 hp Leyland E47/1 petrol engine and Lysholm-Smith transmission used in No.38. The 400 class were double ended with a small passenger compartment and could haul up to two 500 Class passenger trailers.

During the mid-1930's a number of different engines were trialled in the CPH Class. These were a British 150 hp 6-cylinder AEC petrol engine (1933), a US-made 185 hp 6-cylinder Winton petrol engine (1934) and a 120 hp 6-cylinder Leyland diesel engine (1939). Some of these units remained in service for a considerable number of years up to the end of World War II.

Click here for more information about diesel engines

THE MOVE TO AN ALL-DIESEL FLEET

Following World War II, the advances in lightweight diesel engine technology did not go unnoticed by NSWGR. The compact and powerful General Motors (GM) 2-stroke diesel engines were widely used in wartime armoured vehicles and landing craft and in April 1945, a vertical 153 hp 6-cylinder 2-stroke 71 Series Model 6057 GM Detroit Diesel (6/71) engine coupled to a Twin Disc torque converter transmission was fitted to CPH 12. This proved an immediate success and as a result, this engine and transmission package was fitted across all of the surviving CPH and 400 Class vehicles and to No.38 between 1946 and 1957. They were also used to power alternators in the air-conditioned HUB and RUB loco hauled carriage sets.

The provision of the multi-valve cylinder head did not significantly improve the performance problems with the "Harlandic" diesels in the Comet power vans and this led to their replacement with a newer and more powerful GM diesel. The four surviving vans were each fitted with four vertical 250 hp 6-cylinder 2-stroke 110 Series Model 62408 GM Detroit Diesel (6/110) engines. The engines were mounted in facing pairs with the inner engine being mounted higher than the outer one. Each pair drove into a common gearbox through Allison TCLA 965 torque converter transmissions then by cardan shaft to the final drive. Two vertical 82 hp 4-cylinder 2-stroke 71 Series Model 4043 Detroit Diesels (4/71) were installed to provide power for the generators and auxiliaries. These GM engines were installed in the period between 1953 and 1956.

POST WAR CONSTRUCTION

The next type of rail motor was the steel and aluminium branch line 600/700 Class 2-car unit. These 10 sets were built at Chullora Workshops and the 600 Class driving power car was fitted with two vertical 165 hp 6-cylinder 2-stroke 71 Series Model 6081 GM Detroit Diesel (6/71) engine coupled to an Allison TCLA 655 torque converter transmission. This engine and transmission was also fitted to CPH 3 for a period for trial purposes. The 6081 Model was a slightly more powerful version of the 6-cylinder 6057 Model used in the earlier classes.

Closely associated with the development of the 600/700 Class was the main line 900 Class or DEB sets. These air-conditioned trains consisted of two driving power cars and one or two intermediate trailer cars that could be built up to an 8-car train (i.e. two 4-car sets). The 900 and 950 Class power cars were also built at Chullora Workshops and the first two (PF 901 and HPF 951) were fitted with two US-made horizontal 240 hp 6-cylinder 4-stroke Hercules DFXH-F diesel engines coupled to Torcon torque converter transmissions in 1951. The Hercules engines and Torcon converters proved very troublesome in service and the first set was withdrawn from service after less than 6 months in operation. Further construction of the class was suspended until the problems could be corrected. NSWGR turned to the General Motors product and their more powerful 110 Series engines. The Hercules engines and Torcon transmissions were replaced with two inclined 250 hp 6-cylinder 2-stroke 110 Series Model 62802 GM Detroit Diesel engines coupled to Allison TCLA 965 torque converter transmissions. This proved to be reliable combination and construction of the 36 vehicles of the class resumed in 1955 and was completed by 1960. Later vehicles (PF 906-910 and HPF 954-958) built for the Northern Tablelands Express service were fitted with the 250 hp 6/110 Model 62808 engine coupled to an Allison RC3 transmission. The Hercules engines were eventually used in six of the X200 Class Rail Tractors where they proved reasonably successful.

As steam services were being rapidly withdrawn, eighteen 620/720 Class 2-car units entered service from 1961 for suburban and outer suburban use. These closely followed the 600/700 design but were mechanically similar and electrically compatible with the DEB Sets. Six of the early sets were fitted with two horizontal 250 hp 8-cylinder supercharged 4-stroke Rolls-Royce "C" Range Series C8SFLH Model 2126c diesel engines coupled to Rolls-Royce DFR 11500 torque converter transmissions. Rolls Royce C RangeThis engine and transmission package was designed specifically for rail car applications by Rolls-Royce and was also used to successfully re-engine Canadian Pacific and Canadian National Railways Budd rail cars. The Rolls-Royce engines had their superchargers removed later in life as they appeared to cause problems with the water pump. This was subsequently found to be incorrect, however, as the engines were nearing the end of their economic lives the superchargers were not refitted. The superchargers fitted to the Rolls-Royce diesels were nothing more than Roots blowers, similar to that used on the Detroit Diesels. As a result these vehicles then suffered from lack of performance during their latter service life. The reason for selecting Rolls-Royce engines and transmissions is uncertain, however, the company was undergoing financial difficulties during this period and they may well have been offered to NSW Railways at bargain prices. The other eleven of the first seventeen sets were fitted with the later version 900 Class equipment of two inclined 250 hp 6-cylinder 2-stroke 110 Series Model 62808 GM Detroit Diesel engines coupled to an Allison RC3 torque converter transmissions. The last set, 638/738, built in 1968, was designed for hauling a trailer over the steeply graded Murwillumbah Branch and was fitted with two inclined 265 hp 6-cyinder 4-stroke supercharged Cummins NHHRTO-6-B1 diesels coupled to Twin Disc DFFR 10034 torque converter transmissions. This was the first use of Cummins diesel engines in NSW.

A 233 hp 6-cylinder supercharged 4-stroke Rolls-Royce Series C6SFLH version of the engine used in the early 620 Class was deployed in the South Maitland Railways rail cars built by Tulloch in 1961. These vehicles also featured a Rolls-Royce DFR 11500 licence built transmission.

The next rail cars to be built were the five 1100 Class or Budd cars consisting of four power cars and one trailer car. The power cars used two inclined 300 hp 6-cylinder 2-stroke 110 Series Model 62806RD GM Detroit Diesel engines. The 62806RD was a rail car package that had an integrated torque converter transmission. This was the Allison RC3 type transmission but sold under the Detroit Diesel name. The trailer car (BRB 1181) had a horizontal 43 hp 6-cylinder 4-stroke Leyland O.350 diesel to drive the alternator to provide power for the buffet, air-conditioning and auxiliaries. This was a standard Leyland bus engine and was later replaced by a more powerful 50 hp 6-cylinder 4-stroke Leyland O.400 diesel.

The old rail buses of the 1930's were replaced by new construction in 1968. These new Pay Buses featured a 6-cylinder 130 hp Leyland O.400 diesel engine coupled to a Voith DIWA transmission. Leyland buses were in general use in NSW during this period and the builders, Commonwealth Engineering, were among the leading bus manufacturers of the period.

Some 10 years elapsed before any new rail cars were built. In 1971 the unsuccessful 1200 Class or Tulloch cars appeared. These vehicles were fitted with two inclined 292 hp 6-cylinder 4-stroke turbocharged Cummins NTA-855-R diesels coupled to Voith T113r torque converter transmissions. The operational problems experienced with these cars were mainly associated with their complex electrical systems and the engine and transmission package was not the reason for their failure in traffic. Cummins engines and Voith transmissions were later to become the standard fitting for NSW class cars.

By 1972, the 600 Class were becoming unreliable and NSWGR ordered 22 inclined 300 hp 6-cylinder 4-stroke turbocharged Cummins NTA-855-R2 engines and Twin Disc DFFR 10034 torque converter transmissions to re-power the entire class and make them compatible with the 620 and 900 Classes. By this time a number of the early 620 Class were also suffering from overage equipment and in the end only five of the ten 600 Class were fitted with the new engines and transmissions and were converted into the 660 Class. The remainder of the engines and transmissions were diverted to re-power some of the 620 Class units.

In 1978, Japanese Niigata transmissions were trialled with the Cummins NHHRTO-6-B1 diesels in 620 Class unit MPF 638. The success of this trial led to a program to re-engine all of the 900 Class power cars with the later Cummins 335 hp NTA-855-R4 "Big Cam" Series engines and Niigata transmissions. Part way through this program the Niigata transmission was dropped due to operational problems being experienced and the Voith T211r transmission was substituted. The use of The Cummins NTA-855-R4 engine and Voith T211r transmission was later extended to the surviving 620 and 660 Class units.

COMMERCIAL DESIGNS

The Express Passenger Train (XPT) was proposed by Commonwealth Engineering in 1981 as the replacement for loco-hauled country services. The design was based on the British Intercity 125 high speed trains (HST) and adopted the same high performance V-12 4-stroke turbocharged and intercooled Paxman Valenta 12RP200L engine as its British counterpart. However, the power rating was derated to 2,000 hp to cope with higher operating temperatures that are encountered in Australia. The cooling system was also upgraded to meet local conditions. The XPT power car is essentially a single-ended Bo-Bo diesel-electric locomotive and used the same electrical equipment from Brush Traction as the HST.

VP185
Cutaway view of the Paxman VP185 engine
(Courtesy of Paxman Division, MAN Diesel)

The XPT fleet worked on a schedule of very high availability and by the late 1980's engine failures were being experienced throughout the fleet. In the UK, a new lightweight, high performance Paxman engine had been trialled in a number of the 43 Class (HST power car) locomotives. This proved successful in the UK and after a review of world-wide alternatives, the State Rail Authority (SRA) adopted a program to replace the Valenta's in 1993. Conversions were carried out by United Goninan at their works at Broadmeadow, NSW. This new engine was the 2,060 hp V-12 2-stage turbocharged, intercooled and aftercooled 4-stroke Paxman VP185 model 12VP185. This new engine was some 700 kilograms lighter than the Valenta and provided higher performance characteristics.

The next series of railcars were the ABB built Xplorer (long distance) and Endeavour (suburban) series that entered service in 1993. These vehicles (including the non-driving cars) were all powered and featured the usual NSW standard fitting of Cummins diesels and Voith transmissions. However, the design differed from previous practice in that each car had only a single traction engine with a separate diesel powered alternator to provide power for air-conditioning and lighting. Power for traction was provided by a 19-litre 383 kW (514 hp) horizontal 6-cylinder 4-stroke turbocharged Cummins KTA-19R diesel coupled to a Voith T311r torque converter transmission. A Cummins 10-litre 118 kW (158 hp) inclined 6-cylinder 4-stroke turbocharged Cummins LT10R(G) diesel coupled to a Newage Stamford UCI274F alternator provided the auxiliary power supply.

The Hunter rail cars, that entered service in 2006, followed the Endeavour layout but featured an upgraded version of the Xplorer/Endeavour series KTA-19R engine. This is the 19-litre 559 kW (750 hp) horizontal 6-cylinder 4-stroke turbocharged Cummins QSK-19R diesel engine, while the transmission was the Voith T312bre hydrodynamic unit. The auxiliary engine is a 5.9 litre 150 kW (201 hp) 6-cylinder Cummins "B" Series model 6ISBe-G1 diesel engine driving a Newage Stamford UCI274H alternator.

INTERPRETING ENGINE TYPES AND CODES

Some engine manufacturers have codes for their engines that provide an insight into the engine capacities or other details.

Detroit Diesel engines are referred to 4/71 or 6/110 for example. In Detroit Diesel parlance these are interpreted as 4-cylinder 71 Series (4/71) where each cylinder has a capacity of 71 cubic inches or 6-cylinder 110 Series (6/110) where each cylinder is 110 cubic inches capacity.

The Leyland O series engines used the engine capacity in cubic inches where the O.350 and O.400 engines are 350 and 400 cubic inch capacity respectively.

Cummins engines use the engine capacity as part of the coding. Early engines used cubic inches as the measure, such as the NTA-855-R4, where the engine is 855 cubic inches in total capacity. Other parts of the code are "N" for a 4-valve cylinder head, "T" for turbocharging and "A" for aftercooled. The "R" indicated it was specified for railway use and the following number indicates the series of the engine. Later Cummins engines use litres as the measure, such as the KTA-19R that is 19 litre capacity, while the LT10R(G) is 10 litre capacity. The "R" again indicating it was for railway use.

Rolls-Royce engines used a combination of details to describe the specific engine variant. For the C8SFLH used in the 620 Class, the "C" represented the engine model range, the "8" was the number of cylinders, the "S" for supercharged (Roots blown), the "F" for ferrous crankcase, the "L" for left-hand location of the camshaft and the "H" for horizontal rail car arrangement.

ENGINE CROSS REFERENCE TABLE

Manufacturer/Engine

Origin

Cyls

Type

Cycle

No.1

No.2

CPH

No.
38

100

400

600

620

660

900

1100

1200

End
Xpl

XPT

Rail
Bus

Pay
Bus

Hunt

SMR

AEC

UK

6

Petrol

4-stroke

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cummins 6ISBe-G1

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A

 

Cummins KTA-19R

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

Cummins LT10R(G)

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

A

 

 

 

 

 

Cummins NHHRTO-6-B1

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

T

 

 

 

 

 

 

 

 

 

 

Cummins NTA-855-R

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

 

Cummins NTA-855-R2

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

T

T

 

 

 

 

 

 

 

 

 

Cummins NTA-855-R4

US

6

Diesel

4-stroke

  

 

 

 

 

 

 

T

T

T

 

 

 

 

 

 

 

 

Cummins QSK-19R

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

Eveleigh Reversible

AU

6

Petrol

4-stroke

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ford Mercury

US

V8

Petrol

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

Ford Thames

UK

V8

Petrol

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

GM 4/71 Model 4043

US

4

Diesel

2-stroke

 

 

 

 

A

 

 

 

 

 

 

 

 

 

 

 

 

 

GM 6/71 Model 6057

US

6

Diesel

2-stroke

 

 

T

T

 

T

 

 

 

 

 

 

 

 

 

 

 

 

GM 6/71 Model 6081

US

6

Diesel

2-stroke

 

 

 

 

 

 

T

 

 

 

 

 

 

 

 

 

 

 

GM 6/110 Model 62408

US

6

Diesel

2-stroke

 

 

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

GM 6/110 Model 62802RA

US

6

Diesel

2-stroke

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

 

 

 

GM 6/110 Model 62806RD

US

6

Diesel

2-stroke

 

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

 

 

GM 6/110 Model 62808

US

6

Diesel

2-stroke

 

 

 

 

 

 

 

T

 

T

 

 

 

 

 

 

 

 

Harland & Wolff "Harlandic"

UK

8

Diesel

2-stroke

 

 

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

Hercules DFXH-F

US

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

T

 

 

 

 

 

 

 

 

Leyland 15 Litre

UK

6

Petrol

4-stroke

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Leyland 120 hp

UK

6

Diesel

4-stroke

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Leyland E47/1

UK

6

Petrol

4-stroke

 

 

T

T

 

T

 

 

 

 

 

 

 

 

 

 

 

 

Leyland O.350

UK

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

A

 

 

 

 

 

 

 

Leyland O.400

UK

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

A

 

 

 

 

T

 

 

National

UK

4

Diesel

4-stroke

 

 

 

 

A

 

 

 

 

 

 

 

 

 

 

 

 

 

Paxman Valenta 12RP200L

UK

V12

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

 

Paxman VP185 12VP185

UK

V12

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

T

 

 

 

 

Rolls-Royce C6SFLH

UK

6

Diesel

4-stroke

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T

Rolls-Royce C8SFLH

UK

8

Diesel

4-stroke

 

 

 

 

 

 

 

T

 

 

 

 

 

 

 

 

 

 

Thornycroft 42 hp

UK

4

Petrol

4-stroke

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Thornycroft Z6

UK

6

Petrol

4-stroke

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Waukesha

US

4

Petrol

4-stroke

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Winton

US

6

Petrol

4-stroke

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T: Used for Traction - A: Used for Auxiliaries

 

A NOTE ON HORSEPOWER

The horsepower ratings shown on this web site are given from official railway manuals, engine manufacturer's manuals and other source documents. However, the actual measurement of horsepower is subject to a number of different methods and the original documentation does not generally specify which method of measurement was used.

Brake horsepower (bhp) is the measure of an engine's horsepower before the loss in power caused by the transmission, alternator, water pump, and other auxiliary components such as muffled exhaust system. Brake refers to a device which was used to load an engine and hold it at a desired RPM. During testing, the output torque and rotational speed were measured to determine the brake horsepower. More recently, an engine dynamometer is used instead of the brake.

Prior to 1972, American manufacturers rated and advertised their engines in brake horsepower (bhp), frequently referred to as SAE gross horsepower, because it was measured in accord with the protocols defined in SAE standards J245 and J1995. As with other brake horsepower test protocols, SAE gross hp was measured using a stock test engine, generally running with few belt-driven accessories and sometimes fitted with long tube (test headers) in lieu of the OEM exhaust manifolds. The atmospheric correction standards for barometric pressure, humidity and temperature for testing were relatively idealistic.

In the United States, the term bhp fell into disuse in 1971-72, as manufacturers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE net horsepower is measured at the engine's crankshaft, and so does not account for transmission losses. However, the SAE net power testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold.

In the early 20th Century, the British used R.A.C. (Royal Automobile Club) horsepower as measure. This was purely a taxation measurement and does not bear any resemblance to the real performance available from the engine. It was computed as follows:

RAC hp = The bore (in inches) squared multiplied by the number of cylinders divided by 2.5

This measure was responsible for the proliferation of small bore, long-stroke (undersquare) early British engines.