Not all Cosworth engines were YBs. Long before that another twin-cam was well and truly established — and is still going strong today.
Words Jon Hill
Photo Jon Hill
The current crop of BDA-style cam covers for certain modern engines can only mean one thing: the original was extremely good and worthy of copying! Flattery indeed, because the truth is out there — the BDA was one of, if not the best engine that Cosworth has ever produced. There can’t be too many engines that can still hold their own while trouncing the competition 45 years after they were initially designed!
But the BD’s a complicated one since many, many versions exist — in fact there’s probably no such thing as a standard BD — the closest we’ll get are those fitted to the various special versions of the RS Escorts.
To guide us through, we’ve visited one of the most respected engine builders in the country — John Wilcox. He was there at the beginning and knew the original builders, designers and developers — we’re definitely in safe hands!
Cosworth’s Mike Hall designed the BDA as a twin-cam Lotus replacement beginning in May 1967. BD denotes belt driven cams since it’s regarded as a productionised FVA — Cosworth’s then current gear-driven Formula 2 engine — albeit with carbs replacing fuel injection. The Series A part, distinguishes subsequent variations — BDB, BDE and so on.
Meant as a racing engine based on a production block, BDs were Kent-derived like the Lotus and FVA — although using taller Crossflow castings. Originally homeless — despite being fitted to Lotus Cortina test cars and several Capris at their launch in 1969, its production home arrived in 1970, as a replacement for the Lotus-engined Escort Twin Cam, creating the infamous RS1600.
Bore and stroke matched the Crossflow but by detail crank machining, capacity was increased to 1601cc so that it could be homologated into the 1.6 to 2-litre class.
Using the Crossflow, 83.5-mm bore-increasing practise, a 1700cc capacity followed, creating the BDB. Although the 1600 format stuck in 1971, producing the single-seat racecar legend, the BDD Formula Atlantic.
Independent engine designer and builder, Brian Hart produced a 2-litre-potential, alloy block, using Siamesed bores, which was adopted by Ford for the last RS1600s, from September 1972 — subsequently enlarged to 1835cc in the Mk2 Escort RS1800, produced from 1975 to 1977.
Notorious at the time for eating head gaskets, Cosworth weren’t Siamese-bore fans — consequently, they produced their own 2-litre BDF, by machining the 711M block and immersion brazing over-sized liners. In 1973 the infamous, BDG followed — the spec still used to produce 2-litre BDs. Later produced with an alloy block.
Many variants followed even a 1300 using lower height 711Ms (designated BDH, see page 40). But the BDT from 1981 is the most significant Ford version, produced for the turbocharged RS1700T and RS200 from 1983-1986; producing 200 and 250-bhp respectively. Brian Hart topped that with the extended BDT-E, going on to produce an immense 650 bhp in Group B rally cars. The legend carries on though with developments happening all the time.
John Wilcox Competition Engines