M5 Guttyworks

What does it take to justify "ultimate" as a descriptor? If these numbers don't raise your pulse-rate, you're either a librarian or clinically dead. How about 400 hp at 6600 rpm, with 395 lb-ft of torque at 3800 rpm? The press kit comments on the motor's "beefy" torque curve. Radical understatement, gentlemen. Torque? You'll know just how much when you slam the loud pedal and your sternum attempts co-occupancy of the same area as your spine.

It all begins with the MS S52 engine management system. This electro-marvel is derived from the MS S50 unit developed for the M3, and controls...well, basically, the entire known universe. The sun will not rise tomorrow morning unless an MS S52 unit tells it to do so. Officially it controls the ETBC (throttle butterflies), the Servotronic (power steering) unit, the oil circuit switchover, the speed control, the thermal oil level sensor, the rev-counter pre-warning, catalyst protection functions and, ta-daah, the VANOS unit.

The double VANOS ( Variable Nockenwellen Steuerung) camshaft-control system, first seen on the M3, hydraulically adjusts intake and exhaust cam timing. The engine control system senses a number of variables, including throttle butterfly opening and engine speed, and causes a control valve to admit hydraulic fluid from an exhaust-cam-driven pump at very high pressure (above 1000 psi) into a hydraulic piston. The piston is, in turn, connected to the cam-timing sprocket through helical and straight-toothed gears on the operating shaft. As the hydraulic pressure is increased or decreased, the shaft assembly, which has a splined interface with the camshaft, is driven by the piston, and the helically geared portion of the shaft operates on the cam drive sprocket to advance or retard the cam timing.

The object of this exercise, in addition to confusing the hell out of those of us used to more primitive cam timing adjustment, is to advance or retard cam timing to optimize torque and reduce emissions as well as fuel consumption. The theory seems to work, as the engine we tested is the same one coming to the U.S. God help us if the engine management module happens to drop a few lines of code.

If the VANOS system represents high-tech torque, BMW has gone to the other end of the spectrum to find horsepower: They punched the motor out and skied the compression. We've known about these little tricks from Otto's initial attempts at internal combustion, and they still work. The displacement, at 4.941 liters, is up about a half liter from the stock 540i's 4.398 liters. At 11.0:1, the M5's compression ratio shades the 540i's by a full point. We haven't seen numbers like these on the street since the '60s, but BMW NA assures us that the engine will live on the crap-that-passes-for-fuel dispensed at your local mini-mart these days. It will do so, we're told, because of the close control on ignition advance/retard possible with individual cylinder spark control. A separate coil for each cylinder is controlled by the MS S52 system to eliminate the possibility of nasty detonation. Knock sensors on each bank of cylinders are watchdogs for the process.

While we're on the subject of combustible materials, BMW has naturally attended that aspect of the M5 engine performance envelope. For the first time they've used a drive-by-wire system on a motor other than the V12. They call it Electronic Throttle Butterfly Control (ETBC), and it's necessary because each cylinder has its own throttle butterfly. Opening eight of these babies would put too much strain on a conventional cable, hence an electro/mechanical interface. The engine management system senses accelerator position and, in turn, signals an electric motor located in the valley between the heads. The motor drives pushrods which open the butterflies on cylinders 3 and 6, and the other butterflies are on common control rods keyed to these two butterflies. This means that when you boot it you're doing nothing more than actuating a potentiometer. Kind of takes some of the fun out of it, eh? Not to worry. The kick in the butt felt as a result of the action should more than compensate.

Any piece of machinery this complex (read: expensive) deserves oil--lots of it. To this end, BMW developed a "quasi-dry sump" lubrication system for the M series that uses one pressure and two suction pumps. The trick to long engine life under high cornering loads is to scavenge oil from places where it goes in a high-g turn and pump it to where it needs to go. The engine management system does this by sensing (through the Dynamic Stability Control system) the lateral acceleration of the car, and activating oil pickup points to extract oil from outside of the head and sump when hammering through a turn, then pumping it to necessary bearings and the like.

Suspension? It isn't exactly first-generation MacPhersons and semi-trailing arms. Let's begin with steering. The M5 steering system, "Servotronic" to new initiates, is controlled by the engine management system along two curves, dictated by a push-button switch on the dash. The "sport" setting provides less assist and more feedback in the steering as well as actuating the throttle sensor with a quicker ratio.

The car features the existing "light-alloy" 540i suspension, which consists of an aluminum thrust-rod double-joint spring axle at the front and aluminum integral axle with track arms at the rear, with all components "strengthened to meet the far higher dynamic requirements" associated with an M-car. It's been lowered by 0.60 in. at the front and 0.39 in. at the rear. Shock valving has been tightened and spring rates are up, in keeping with the sporting nature of the car. Suspension bushings are made of a denser material than stock, and sway bar stiffness has changed to maintain neutral handling at higher cornering forces. Both front and rear suspensions use "polyurethane springs" on top of the dampers. The thing handled like a slot car before the M-label version. When it ain't broke, beef it up and let it ride. We're good to go.

But are we good to stop? For the "Go 'til you see God, then BRAKE!" segment of our readership, I have good news. This iteration of the BMW dream uses compound brakes on the front and rear binders. Translation: the rotor/hub assembly is multipiece, allowing a 15-percent weight saving. Additionally, the friction disc (which is separate from the hub and "floats" on a radial anti-friction bearing), dissipates heat without thermodynamic linking to the inner guttyworks. Therefore, no more warped brake rotors. The 13.58-in. diameter front and 12.91-in. diameter rear rotors act with single-piston calipers to halt the beast. Single piston? Yipes! Hey, GM trusts single-piston calipers to halt my three-ton Suburban, and the M5 stops straight, true and quickly.

Assisting us in those non-lumpy stops, as well as all sorts of twisty bits, is the biggest wheel/tire combo BMW has ever installed on a car. The fronts are 245/40-18Zs, and the rears are an incredibly meaty 275/35-18Z. The press cars were running Dunlop Sport 8080s, with a very aggressive tread pattern. This may cause apprehension, since rubber with the aspect ratio of a forklift tire has a tendency, when coupled with a sporting suspension, to promote just a touch of retina-detaching harshness over large imperfections in the road, such as a human hair. The amazing thing about Motorsport's wheel/tire/suspension combo is that BMW has managed to coordinate the elements to provide a firm feel without the obligatory spanking associated with cornering prowess.

The rest, as they say, is flim-flammery. Put this bad ride on the track, where it belongs, and you will be king. Put it on the road, and nothing comes within light years. The brochure accompanying a really neat crystal cube with the miraculous BMW V8 etched in three dimensions says it all: "Alea iacta est: the dice have been cast." Well, M-B, Lexus, you other posers and wannabes, cash 'em in and move it out: BMW just rolled another seven.