The YB series of 1,993 cc (121.6 cu in) from Pinto OHC Based and were introduced in the road-going Ford Sierra Cosworth in 1986 with 204 bhp (152 kW). It was the best route going engine that developed much than 100 bhp (75 kW) per litre, with 5,000 units built for Group A homologation purposes, both for rallies and racing cars. Racing versions could produce about 400 bhp (300 kW). A modest version development example was introduced in 1987, the RS500, with ability now exceeding 550 bhp (410 kW) in complete racing thim. The RS500 came to rule touring car racing in its prime. Today there are many route going YB engines developing over 800 bhp (600 kW) and there are several rallycross Sierra Cosworths utilizing YB engines tuned to over 900 bhp (670 kW.) The Rev Hard drag racing squad take a Cosworth YB in their Escort Cosworth automobile that develops 1,100 bhp (820 kW) whilst yet retaining the old 2,000 C.C. capability.Further evolutions of the YB included a reduced-emissions route edition, as easily as the block used in the Escort RS Cosworth (which used the Sierra floor pan. The engine model stopped being used on original cars in 1997, with the Focus WRC and road-going Focus RS relying on Zetec E engine designs