BMW is expanding its 3-series convertible and 1-series coupé ranges with a couple of old friends: the 2.0-litre diesel and 3.0-litre straight-six engines.The diesel goes into the drop-top version of the 3-series; it's in the same spec as regular 320d models, which means 174bhp, 251lb ft and 140g/km of CO2. BMW claims a 0-62mph time of 8.6sec and a top speed of 139mph.The 1-series coupé, meanwhile, moves up to four model variants by getting the firm's familiar 3.0-litre, straight-six engine. The motor produces 215bhp and 184lb ft of torque; BMW claims the 125i can crack 0-62mph in 6.4sec and a top speed of 152mph, while returning 35.8mpg combined.Both of the new models will go on sale in March. The 320d SE convertible costs £33,110, while the M Sport variant is priced at £35,735. The 125i coupé SE costs £23,195, while the M Sport model weighs in at £25,050.