Cosworth simply weren’t keen on the turbo movement. Keith Duckworth (the ‘worth’ in Cosworth) was once quoted as saying about Renault’s fledgling turbo efforts that “it’ll never bloody work and if it does it should be banned.”
The company was simply too slow to see what was coming. It wasn’t alone in this respect, the likes of Williams and especially Tyrrell were both well behind the curve on this in contrast to the likes of Renault, Ferrari and McLaren. Consider also that the turbo era also saw the start of the rise of the manufacturers in F1 with Renault, BMW and Honda all entering the sport in the late 1970s/early 1980s. Cosworth simply couldn’t compete without support from Ford, who were never very good at exploiting the marketing potential of their involvement in F1.
Developing a fully competitive, reliable turbo engine took time, as shown by Honda, BMW and Renault’s early experiences. Cosworth introduced its own turbo engine for 1986 which was powerful but unreliable and thirsty compared with Honda’s much more refined V6. But by then moves were already underway to restrict the turbos and an outright ban from 1989 was announced at the end of ’86. So there seemed to be little point in spending good money to develop an engine that was shortly to be obsolete anyway.
Cosworth kept the turbo engine for 1987 but dropped it for 1988 when, wrongly as it transpired, it was assumed that normally aspirated engines would have the edge over the increasingly fuel and boost-restricted turbos. So Cosworth went back to the DFV which (badged as the DFR) competed in F1 until the end of 1991, although works team Benetton had access to the new HB from 1989.
1: The DFV got a new lease of life with the skirted ground effect cars, due to its more compact dimensions compared with the F12, V12 and turbo’s allowing better aerodynamic packaging.
2: Cosworth problem in part was their success, the DFV was also basis for not only a successful business supplying the independant F1 teams, but also for Indy Car, endurance racing, power boats etc. It was simply had too much too loose in betting the business on an expensive Turbo development programme, until Ford provided the cash.