Three tur­bocharg­ers give BMW ex­tra power

Yorkshire Post - Motoring - - FRONT PAGE - Fred­eric Manby

BMW is of­fer­ing its most pow­er­ful diesel to date in the re­vised X6 and the X5, known as M50d mod­els. The en­gine is the fa­mil­iar 3-litre straight six lay­out, this time, and a first, with three tur­bocharg­ers. One of two small tur­bocharg­ers starts blow­ing at en­gine speeds just above idle, giv­ing “in­stant re­sponse” to any move­ment of the ac­cel­er­a­tor. As the revs in­crease to 1,500rpm the ex­haust gas reaches the large tur­bocharger, en­sur­ing that peak torque of 545 lb-ft is at­tained and main­tained from 2,000rpm un­til 3,000rpm. At 2,700rpm a vac­uum-mod­u­lated ex­haust flap opens al­low­ing ex­haust gas to flow past the sec­ond small tur­bocharger cre­at­ing ad­di­tional charge pres­sure, al­low­ing max­i­mum power of 376 bhp to be avail­able from 4,000 to 4,400rpm. If the large tur­bocharger is spin­ning at par­tic­u­larly high speeds a vac­uum reg­u­la­tor opens a waste­gate valve to re­lieve pres­sure and so avoid un­wanted ex­haust back pres­sure.

The X6, with a re­vised face and other de­tail changes, goes on sale on June 16, priced from £46,725. The high per­for­mance M50d model costs £62,260 and is quoted at 36.7mpg, 204g/km of CO2 and 0-62mph in 5.3 sec­onds. The X5 M50d has sim­i­lar fig­ures but man­aged 199g/km of CO2 and costs £60,325.


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