Gordon Murray then approached BMW, which took an interest, and the motorsport division BMW M headed by engine expert Paul Rosche[8] designed and built Murray a 6.1 L (6,064 cc) 60-degree V12 engine called the BMW S70/2.[9] At 627 PS (461 kW; 618 hp)[10][11][12] and 266 kg (586 lb) the BMW engine ended up 14% more powerful and 16 kg (35 lb) heavier than Gordon Murray’s original specifications, with the same block length. It has an aluminium alloy block and heads, with 86 mm (3.4 in) x 87 mm (3.4 in) bore/stroke, quad overhead camshafts with variable valve-timing (a relatively new and unproven technology for the time) for maximum flexibility of control over the four valves per cylinder, and a chain drive for the camshafts for maximum reliability. The engine uses a dry sump oil lubrication system. The carbon fibre body panels and monocoque required significant heat insulation in the engine compartment, so Murray’s solution was to line the engine bay with a highly efficient heat-reflector: gold foil. Approximately 16 g (0.8 ounce) of gold was used in each car.[13] The road version used a compression ratio of 11:1 to produce 627 hp (468 kW; 636 PS)[9] at 7400 rpm and torque output of 480 lb·ft (651 N·m) at 5600 rpm.[14] The engine has a redline rev limiter set at 7500 rpm. In contrast to raw engine power, a car’s power-to-weight ratio is a better method of quantifying acceleration performance than the peak output of the vehicle’s powerplant. The standard F1 achieves 550 hp/ton (403 kW/tonne), or just 3.6 lb/hp. The cam carriers, covers, oil sump, dry sump, and housings for the camshaft control are made of magnesium castings. The intake control features twelve individual butterfly valves and the exhaust system has four Inconel catalysts with individual Lambda-Sondion controls. The camshafts are continuously variable for increased performance, using a system very closely based on BMW’s VANOS variable timing system for the BMW M3;[15] it is a hydraulically actuated phasing mechanism which retards the inlet cam relative to the exhaust cam at low revs, which reduces the valve overlap and provides for increased idle stability and increased low-speed torque. At higher rpm the valve overlap is increased by computer control to 42 degrees (compare 25 degrees on the M3)[15] for increased airflow into the cylinders and thus increased performance. To allow the fuel to atomise fully, the engine uses two Lucas injectors per cylinder, with the first injector located close to the inlet valve – operating at low engine rpm – while the second is located higher up the inlet tract – operating at higher rpm. The dynamic transition between the two devices is controlled by the engine computer.[15] Each cylinder has its own miniature ignition coil. The closed-loop fuel injection is sequential. The engine has no knock sensor as the predicted combustion conditions would not cause this to be a problem. The pistons are forged in aluminium. Every cylinder bore has a nikasil coating giving it a high degree of wear resistance.[15] From 1998 to 2000, the Le Mans–winning BMW V12 LMR sports car used a similar S70/2 engine. The engine was given a short development time, causing the BMW design team to use only trusted technology from prior design and implementation experience. The engine does not use titanium valves or connecting rods. Variable intake geometry was considered but rejected on grounds of unnecessary complication.[15] As for fuel consumption, the engine achieves on average 15.2 mpg (15 L/100 km), at worst 9.3 mpg (25 L/100 km) and at best 23.4 mpg (10 L/100 km).[3]
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