We make no bones about being huge fans of Cosworth, what with Northamptonshire’s finest having produced some of the most successful engines in race and rally history, not to mention the Duratec now powering the rear wheel of our own Murray Mk1 Escort. You could say we’re biased…and we’d readily admit to such an accusation!
Today though, it’s time to look at another altogether less well known but no less worthy example of Cosworth’s engineering prowess, the KF. The engine was borne from Opel’s desire to take the fight to Mercedes and Alfa Romeo in the DTM of the mid ’90s, and its technical sophistication, spec and output make for compelling reading today, well over 20 years on from its conception.
First though, some history. The DTM, or Deutsche Tourenwagen Meisterschaft to its friends, had grown in both spectacle and popularity as the ’80s progressed. What had begun the decade as a resolutely production car based concern, home to the likes of the RS500 and E30 M3, had morphed into one of the most technically liberated race series on the face of the planet. The biggest change was the switch from Group A to Class 1 Touring Car regulations in the lead up to the 1993 season, a move which cemented the DTM’s position as the most advanced ‘tin top’ series on the face of the earth.
How sophisticated? Well, come the middle of the decade your average DTM car was at least as technically advanced than a comparable F1 machine of the same era, and in many cases more so. Traction control, ABS (amongst other driver aids) and four-wheel drive were both par for the DTM course, all of which were outlawed from F1. Factor in Works teams and associated budgets for Mercedes, Alfa Romeo and Opel, and it was clear that things were set to explode from a race car engineering perspective.
Reasoning that there were few companies better placed to produce them a race winning engine, Opel enlisted the help of Cosworth to develop an engine for its Calibra DTM racer. The new engine, now codenamed the ‘KF’ in line with Cosworth nomenclature, was an all alloy, 2.5 V6 with a 75 degree V-angle. It tipped the scales at a mere 190lb and its block was approximately the same size as a shoebox, so to call it compact would be doing Cosworth’s engineering team a disservice.
It was also powerful, making well over 500bhp at launch and as much as 550bhp come the end of its development cycle, and could rev as high as 12,000rpm. Suffice it to say, it sounded like nothing else on earth.
In many ways the mid ’90s were the last gasp of the limitless motorsport budget, and this was reflected in the design of engines like the KF. The lifespan of each engine was measured in mere km and each was expected to last no more than a race meeting at most, sometimes a mere session or race. This meant design tolerances could be wafer thin, and also that Cosworth’s engineers could truly ‘go to town’ in terms of engineering flair.
One of the best ways of appreciating just how advanced the KF was, is to take a look at its power output through the prism of good old fashioned maths. This reveals an engine with a power to weight ratio of 2.84hp per lb., which sounds fairly innocuous by the standards of today. It’s easier to put that figure into perspective, however, when you realise that it’s equivalent to that Retropower favourite, the C20XE, making a naturally aspirated 687bhp!
The KF was mounted to one of Xtrac’s most impressively engineered transmission, one that routed drive around the Calibra before doling it to both axles via a series of differentials. Power was routed through a six-speed sequential, then to a pair of half-shafts which effectively encased the block of the engine. It promised the kind of weight distribution Opel’s rivals could only dream of, and helped make the Calibra one of, if not the best, handling car on the DTM grid.
It nevertheless took the Opel-Cosworth concern to prove its worth, with the might of Alfa and Mercedes proving unbeatable for much of the Calibra’s DTM career. In 1996 though, things came good for Russelheim and Northampton, and in the final year of the Class 1 Touring Car era. The DTM had expanded to become the International Touring Car Championship by this point, and while it was every bit as spectacular as ever it was also crushingly expensive. The likes of Opel and Alfa had also begun to question why they were racing in both Japan and Brazil, countries were they no longer sold cars.
To cut a long story short, the DTM/ITCC collapsed in acrimonious fashion at the end of the 1996, but not before Opel’s Manuel Reuter had taken his KF-powered Calibra to a famous victory, allowing the company to retire on a high.
The KF lived on for a few more years as the power plant of choice for some of Europe’s most potent hill climbers, and in the UK, the formative engine for Andy Burton’s legendary Peugeot 306 Cosworth rally car. It was modified and de-tuned for a life spent on the gravel stages of the BTRDA, but it sounded every bit as glorious and introduced legions of British rally fans to the KF’s innate brilliance.