McLaren F1: Power and Engineering
The engine’s got masses of torque, it’s sweet, crisp, it’s the most glorious engine I’ve ever driven. This is like no engine you’ve ever heard.
— Jonathan Palmer | Autocar
Gordon Murray insisted that the engine for this car be naturally aspirated to increase reliability and driver control. Turbochargers and superchargers increase power but they increase complexity and can decrease reliability as well as introducing an additional aspect of latency and loss of feedback. The ability of the driver to maintain maximum control of the engine is thus decreased.
Murray initially approached Honda for a power plant with 550 bhp (410 kW; 558 PS), 600 mm (23.6 in) block length and a total weight of 250 kg (551 lb), it should be derived from the Formula One power plant in the then-dominating McLaren/Honda cars.
When Honda refused, Isuzu, then planning an entry into Formula One, had a 3.5-litre V12 engine being tested in a Lotus chassis. The company was very interested in having the engine fitted into the F1. However, the designers wanted an engine with a proven design and a racing pedigree.
BMW S70/2 V12
Then BMW took an interest, and the motorsport division BMW M headed by engine expert Paul Rosche designed and built Murray a 6.1 L (6,064 cc) 60-degree V12 engine called the BMW S70/2. At 627 hp (468 kW; 636 PS) 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 aluminum 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.
The road version used a compression ratio of 11:1 to produce 627 hp (468 kW; 636 PS) at 7400 rpm and torque output of 480 lb·ft (651 N·m) at 5600 rpm. 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 power plant. The standard F1 achieves 550 hp/ton (403 kW/ton), 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; 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) for increased airflow into the cylinders and thus increased performance.
To allow the fuel to atomize 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. 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.
BMW V12 LMR
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. 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).
Steve Randle, who was the car’s dynamicist, was appointed responsible for the design of the suspension system of the McLaren F1 machine. It was decided that the ride should be comfortable yet performance-oriented, but not as stiff and low as that of a true track machine, as that would imply reduction in practical use and comfort as well as increasing noise and vibration, which would be a contradictory design choice in relation to the former set premise — the goal of creating the ultimate road car.
From inception, the design of the F1 vehicle had strong focus on centering the mass of the car as near the middle as possible by extensive manipulation of placement of, inter alia, the engine, fuel and driver, allowing for a low polar moment of inertia in yaw. The F1 has 42% of its weight at the front and 58% at the rear, this figure changes less than 1% with the fuel load.
The distance between the mass centroid of the car and the suspension roll centre were designed to be the same front and rear to avoid unwanted weight transfer effects. Computer controlled dynamic suspension were considered but not applied due to the inherent increase in weight, increased complexity and loss of predictability of the vehicle.
Damper and spring specifications: 90 mm (3.5 in) bump, 80 mm (3.1 in) rebound with bounce frequency at 1.43 Hz at front and 1.80 Hz at the rear. Despite being sports oriented, these figures imply a soft ride and inherently decrease track performance. As can be seen from the McLaren F1 LM, McLaren F1 GTR et al., the track performance potential is much higher than that in the stock F1 due to fact that car should be comfortable and usable in everyday conditions.
The suspension is a double wishbone system with an unusual design. Longitudinal wheel compliance is included without loss of wheel control, which allows the wheel to travel backwards when it hits a bump – increasing the comfort of the ride.
Castor wind-off at the front during braking is handled by McLaren’s proprietary Ground Plane Shear Centre — the wishbones on either side in the subframe are fixed in rigid plane bearings and connected to the body by four independent bushes which are 25 times more stiff radially than axially. This solution provides for a castor wind-off measured to 1.02 degrees per g of braking deceleration. Compare the Honda NSX at 2.91 degrees per g, the Porsche 928 S at 3.60 degrees per g and the Jaguar XJ6 at 4.30 degrees per g respectively. The difference in toe and camber values are also of very small under lateral force application. Inclined Shear Axis is used at the rear of the machine provides measurements of 0.04 degrees per g of change in toe-in under braking and 0.08 degrees per g of toe-out under traction.
When developing the suspension system the facility of electro-hydraulic kinematics and compliance at Anthony Best Dynamics was employed to measure the performance of the suspension on a Jaguar XJR16, a Porsche 928S and a Honda NSX to use as references.
Steering knuckles and the top wishbone/bell crank are also specially manufactured in an aluminum alloy. The wishbones are machined from a solid aluminum alloy with CNC machines.
The McLaren F1 uses 235/45ZR17 front tires and 315/45ZR17 rear tires. These are specially designed and developed solely for the McLaren F1 by Goodyear and Michelin. The tires are mounted on 17-by-9-inch (430 mm × 230 mm) front, and 17-by-11.5-inch (430 mm × 290 mm) rear five-spoke cast magnesium wheels, coated with a protective paint and secured by magnesium retention pins.
The turning circle from curb to curb is 13 m (43 ft), allowing the driver 2 turns from lock to lock.
The F1 features unassisted, vented and cross-drilled brake discs made by Brembo. Front size is 332 mm (13.1 in) and at the rear 305 mm (12.0 in). The calipers are all four-pot, opposed piston types, and are made of aluminum. The rear brake calipers do not feature any handbrake functionality, however there is a mechanically actuated, fist-type caliper which is computer controlled and thus serves as a handbrake.
To increase caliper stiffness, the calipers are machined from one single solid piece (in contrast to the more common being bolted together from two halves). Pedal travel is slightly over one inch. Activation of the rear spoiler will allow the air pressure generated at the back of the vehicle to force air into the cooling ducts located at either end of the spoiler which become uncovered upon application of it.
Servo-assisted ABS brakes were ruled out as they would imply increased mass, complexity and reduced brake feel; however at the cost of increasing the required skill of the driver.
Gordon Murray attempted to utilize carbon brakes for the F1, but found the technology not mature enough at the time; with one of the major culprits being that of a proportional relationship between brake disc temperature and friction — i.e. stopping power — thus resulting in relatively poor brake performance without an initial warm-up of the brakes before use. Since carbon brakes have a more simplified application envelope in pure racing environments, this allows for the racing edition of the machine, the F1 GTR, to feature ceramic carbon brakes.
Gearbox and Powertrain
The standard McLaren F1 has a transverse 6-speed manual gearbox with an AP carbon triple-plate clutch contained in an aluminum housing. The second generation GTR edition has a magnesium housing. Both the standard edition and the McLaren F1 LM have the following gear ratios:
With a final drive of 2.37:1, the final gear is offset from the side of the clutch. The gearbox is proprietary and was developed by Weismann. The Torsen LSD (Limited Slip Differential) has a 40% lock.
The McLaren F1 has an aluminum flywheel that has only the dimensions and mass absolutely needed to allow the torque from the engine to be transmitted. This is done in order to decrease rotational inertia and increase responsiveness of the system, resulting in faster gear changes and better throttle feedback. This is possible due to the F1 engine lacking secondary vibrational couples and featuring a torsional vibration damper by BMW.
- McLaren Automotive
- Wikipedia: McLaren F1