#Tech – The Cosworth BD engine.

Cosworth was founded in 1958 by Mike Costin and Keith Duckworth. It has become the most successfull engine manufacturer in history. The number of driver and manufacturer titles to its credit in a wide range of formulae with impressive performances in Formula 1, IRL, Champ Car, WRC, sportscars and MotoGP are the best testimony of the capabilities available at their office.

The first ever victory came with the Cosworth tuned Ford 105E Formula Junior engine in 1960 with Jim Clark driving the equipped Lotus 18 to outright win. Later, in 1967, it would introduce the Cosworth DFV V8 in Formula 1 through the Lotus 49. They would set the trend for the coming years with their revolutionar design taking 155 wins in 15 years.

But let’s talk about the most declined engine they’ve build, the Cosworth BD serie.

In 1967 Harley Copp, Walter Hayes and Henry Taylor reached an agreement with Cosworth to develop an engine for Ford of England. The objective was to develop and engine with better performance than the twin-cam Lotus-Ford.

Keith Duckworth was engaged full-time on the DFV engine so Mike Hall took on the design responsibilities. The new engine was based on the Ford Kent block and would use the same basic cylinder head breathing as the earlier FVA 4-cylinder and the V8 DFV.

The agreement between Ford and Cosworth was for the design and development, not the building of engines. Design started in May of 1967 and the first 1600cc engine ran in June of 1968. The BDA means Belt-Drive Series A, which refers to the way the camshafts were driven. When introduced it was the first British engine to use cogged belts to drive the camshafts.

From Cosworth’s perspective the BDA took on a life of its own. In 1970 the BDB version was introduced. This was developed for Ford for use in the Escort RS1600 for rallying. The bore was increased for a capacity of 1700cc. According to Cosworth’s Mike Hall, the BDA just snowballed into the “Meccano set” of engines. By the mid-1970s the various BD engines accounted for over half of Cosworth’s turnover. Modifications were introduced by Cosworth and several other companies. The company continued to produce kits of parts to build up BD engines into the 1980s.

1969, The BDA, 1601cc, 120 HP

Cosworth increased its association with Ford in 1969, by developing a double overhead camshaft (DOHC) 16-valve inline four-cylinder engine for road use in the Ford Escort. Working from the Kent block, Cosworth created a 1,601 cc for homologation purposes. 

The camshafts were driven by a toothed belt, hence the name BDA, literally meaning “Belt Drive, A type”. Running in Group 2 and Group 4 on either rallying or touring car racing, this engine could be enlarged to a maximum of 2,000 cc. 

The nominal homologation at 1,601 cc capacity meant that BDA-engined cars competed in what was usually the top class (1600 cc and up) so were eligible for absolute victories rather than class wins.

1973, The BDG, 1975cc, 275 HP

The BDG was the evolution of the BDE built for Formula 2. The BDF was an improved development of the BDE. In 1973 the BDG was introduced, it featured another increased cylinder capacity and produced 275 bhp. The first versions had a cast iron block, but later engines had an aluminum block.

The BDG had a capacity of 1975cc/120.5 cu in. The compression ratio was 12.0 to 1 for a horse power rating of 280 at 9250 rpm. The cylinder numbering was 1 – 2 – 3 – 4 front to rear with a firing order of 1 – 3 – 4 – 2 .

The BDG became the most commonly used engine from 1973, being used from Formula 2 to the Le Mans sportscars such as the later Chevron B36.

Chevron B36 BDG
Chevron B36 BDG
Type Year Size Output Description
BDA 1969 1601cc 120 Bhp. Belt Drive layout similar to FVA on taller Kent block
BDB 1970 1700cc 200 Bhp. Escort RS1600 rally engine, sold as kits
BDC 1970 1700cc 230 Bhp. Injected BDB for Group 2 Escort RS1600, also kits
BDD 1971 1600cc 200 Bhp. Definitive Formula Atlantic Motor, also kits
BDE 1972 1790cc 245 Bhp. Formula 2 first stretch to 2 litre rules, bigger bore, injection
BDF 1972 1927cc 270 Bhp. Formula 2 next stretch, liners brazed in to cast iron block, very successful
BDG 1973 1975cc 275 Bhp. Formula 2 and rally, development of BDF, later with aluminum block
BDH 1973 1300cc 190 Bhp. Group 2 Sports cars, shorter stroke on shorter block
BDJ 1974 1098cc 150 Bhp. Formula C, short stroke version for SCCA
BDK Unused
BDL experimental turbo
BDM 1975 1599cc 225 Bhp. Formula Atlantic, big valve, injected BDD
BDN 1977 1600cc 210 Bhp. Formula Atlantic, Canadian Atlantic sealed motors this year only, sold as kits
BDO Unused
BDP 1984 1975cc 245 Bhp. Sprint car, aluminum block, BDG bore/stroke, injected, methanol
BDQ Unused
BDR 1983 1601cc 120 Bhp. BDA kits for Caterham Super Sevens, also 1.7 litre and 150, 170 Bhp.
BDT 1981 1778cc 200 Bhp. RS1700T turbo, aluminum block, kits for JQF
1981 1803cc 250 Bhp. RS200 BDT units redesigned, rebuilt, and enlarged
BDT-E 1986 2137cc 500 Bhp. Evolution BDT by Brian Hart, Ltd.

15 thoughts on “#Tech – The Cosworth BD engine.

  1. I think you may be in error with respect to the statement that the BDA was the first UK belt drive production engine – the Vauxhall Slant-4 1.6 and 2 litre engines went into production in Sept 67 whereas the RS1600 Escort replaced the Twin Cam in 68?

    The first US timing belt engine was the I6 in the ’65 Pontiac Tempest (a John DeLorean project!)

    Even before that was the 1961 or 2 Glas (a German brand, later swallowed by BMW) and that was the first production car implementation. However, the construction of the Glas belt was different from the Uniroyal used by GM and upon which all subsequent belts have been based

  2. One of the most successful BD variants was built by Brian Hart Ltd in Harlow Essex for the 1972 European F2 Series. This was at 1860cc and utilized a special Siamese bore cast iron block made specifically for racing by Ford. This engine made around 265/270bhp and was used by Team Surtees drive Mike Hailwood to win the championship. It was also used by many other teams and drivers that year and ‘73.
    I know…..I built many of them and all of the ones used by Mike the Bike.
    We spent a long time selecting the blocks by measuring the Siamese bore wall thicknesses to obtain the ones that had the best overall average wall thickness. Our cylinder heads were all modified in house by a great chap…Broddler Bill ….and had our own valves bigger than Cosworthand we also used Mahle pistons…..great times !
    Brian was also the first to develop the alloy block for the BD using it initially in the 2Liter sports car series and it was designated Hart 420S
    This is not to be confused with the 420R which was a completely different engine with much bigger bores and bore spacing, longer than a BD
    We built all the Ford Escort factory rally engines and their team manager Peter Ashcroft was great friends with Brian and one evening Peter actually clipped his ankle on a covered block and what did he discover….the Hart Alloy BD block….true story. It was then discussions began and ultimately Ford bough the rights to the Hart Alloy BD block
    I was employed by Brian for almost 9 fantastic years. Some of the best in my life….

    1. Hi David
      I’m researching Max Bonnin’s March 732 which is listed at some events using a Hart BDA. I wonder if it had the alloy block 2 litre.
      Do you recall the use of the Hart alloy block in F2 before the alloy BDG became available?

    2. Hi David
      I’m researching Max Bonnin’s March 732 which is listed at some events using a Hart BDA. I wonder if it had the alloy block 2 litre.
      Do you recall the use of the Hart alloy block in F2 before the alloy BDG became available? I see listings for Chevron, Surtees and GRD F2 cars using Hart BDA in 1974 also. Do you think these might have been alloy blocks?

    3. Thanks for the Comment David, did you meet Guy croft? was the first rs1600 block the same as the kent block? are they all interchagable? or are there differences that make them bespoke to each application?

    4. Interesting that you had to select engine blocks from what were special siamese blocks!…..What did you do with the rejects?!

  3. How do you tell the size of a BDA engine in cc ìe 1600 or a 2000cc ?

    1. Hi Ruedi Gygax. In the 1970s I worked with John Lievesey. John was and ex-Cosworth man and also ex Ford Competitions. He set up his own business in around 1969/70. John and Brian Hart were very close and John used to do all the valve gear design for Hart. Lievesley built many successful rally engines and also built Formula Atlantics. We found it very hard to match the power output of the Nicholson engines so Nicholson must have been pretty clever!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s