Imagine
You're driving along in your new BMW M5: 400 horsepower on tap, and you feel unstoppable. As you approach a red traffic signal, you notice two black 5 Series BMWs in your rearview mirror, and they proceed to line up on either side of you. The one on the left is sporting an M5 front bumper cover and lip spoiler, but by the profile it's obvious this is just a basic 5 Series with some nice wheels. You peep over to your right, and it's quite evident this car is no M5, either.
The cross street's signal turns yellow, and you start to bring up the revs. The light turns green and, in an instant, what you thought would be two, sub-300-bhp cars innocently chirping their H-rated tires instead turn your world upside-down with the roar of tarmac-shredding, boosted rockets that instantly leave you behind, embarrassed. By the time you're halfway into fourth gear and a few car lengths back, you realize your fate and slow down.
Do you think this could ever happen? After a short hunt, we found a pair of 5 Series BMWs on the West Coast that made it clear this scenario could take place. What choice had we but to test the two cars against each other?
The 540i
The styling of Jimmy Wu's 1998 540i is subtle, very similar to a car we featured in our March 2002 issue-oh, wait, it's the same one. The styling is accented with Euro clear turn signals, a BMW aerodynamic front spoiler and a xenon light conversion. It rolls on AC Schnitzer Type III wheels, sized 8.5x19 for the front and 9.5x19 for the rear, wrapped with Pirelli P Zero Rosso tires, size 245/35-19 front and 275/30-19 rear...sizes which aren't very subtle-looking at all.
The car's tasteful look doesn't shed much light on any performance upgrades until you notice the Dinan trunk badge and the binders sporting the Brembo logo. The Gran Tourismo kit consists of 14-in. two-piece floating rotors sandwiched by four-piston calipers in the front, with slightly smaller 12.9-in. rotors in the rear.
About that Dinan badge: The noted tuning company gives them only to customers who have have accumulated at least 10 "points" of Dinan performance upgrades. This car is well over that 10-point minimum. In this case, let's just say it's good this big brake system was installed because of what this car packs under the hood: Dinan's centrifugal supercharger system, using a Vortech blower, added to the already powerful 4.4L V8 motor. To maximize the installation, other Dinan products were added, including a Cold Air Intake, hi-flow air mass sensor, bigger throttle body and a high-flow intake manifold. Fuel and spark timing is managed by Dinan's Stage V software upgrade, and the car exhales via a Dinan free-flow exhaust with custom fittings.
The factory 10.0:1 compression ratio was retained, and the blower pumps out a healthy 8 psi of boost. A stock 540i V8 is already a torque monster, but add to that about 100 more lb-ft, and you get the idea-this car is a sleeper, a Q-ship, a surprise waiting to happen to hapless M5 owners.
To harmonize handling performance with the augmented power, the 5er received a Dinan Stage III suspension system, which includes specially valved dampers with matching spring rates, a set of anti-roll bars and front camber plates. It also sports front and rear strut and shock braces for added chassis stiffness. The result is still a heavy car but with the nimbleness of an E39 M5 and ride quality worthy enough to call it a luxury sports sedan.