Tech Analysis: BMW E39 M5

Ten years ago, when you thought about a family sedan, how often did the words, "six-speed" or "400 bhp" come to mind? Today, however, the words family sedans and powerful are almost synonymous. Case in point: Mercedes-Benz has a few that are knocking on the 500-bhp door. And BMW's new 2005 M5 will be doing the same.

With BMW winding out the last of its E39 M5 sales, I thought it would be appropriate to explore the sedan's performance potential. With some basic bolt-on modifications, I hoped to place the E39 M5 in the elite group of monster horsepower sedans. In this first part of a two-part series, I think we're already there.

Although rated at 400 bhp, M5s are typically dynoing between 300 to 335 hp at the wheels (SAE corrected) on the widely used Dynojet 248C dynamometer, with a few exceptions slightly higher than that. For this test, I used a 2002 M5 owned by Dr. Ronny Ghazal, an orthopedic surgeon in Redlands, Calif.

With absolutely no upgrades this car already seemed extraordinarily fast. We took it to Vadim Federovsky of evosport inc, and he concurred: "This is one strong M5!" evosport technicians strapped the car to the dyno and, sure enough, this car was making well above normal power--344.7 hp to the wheels.

This good news started to place doubt in my mind as to whether I'd be able to see any gains at all with some basic bolt-on upgrades. Maybe the exhaust on this particular car was a perfect specimen, or maybe the factory tuning is unbeatable. I gave it a shot anyway.

Initially, I told the M5 owner that if I got a 20-hp peak gain at the wheels I'd be happy. I also promised that it would in no way involve going inside the engine. All I had in mind was software, exhaust, pulleys and replacement air filter upgrades.

The first of the tests involved the cat-back exhaust and software. Supersprint's quality exhaust systems have been tested on a variety of cars here at european car: the Volkswagen Jetta 1.8T, Mini Cooper S and a few E36 BMWs, including 3.0- and 3.2-liter M3s, and a 325is. The Italian company states it performs more than 1,000 dyno test runs each year. I've always liked the quality and overall build of the exhaust systems, so I ordered one from Supersprint North America's primary distributor of BMW-specific exhaust systems, BMP Design.

With a retail price of just over $1,700, the Supersprint exhaust features left and right mufflers and a crossover midsection pipe. The entire system is TIG welded stainless steel with mandrel-bent, 1.5mm tubing. The factory system was pulled off the car as one piece, weighing in at more than 93 lb. The three-piece Supersprint system weighed 57 lb, good for a 36-lb weight loss.

evosport's software for the E39 M5 was designed as a "Stage 1" software program to run with the Supersprint exhaust system, so I decided to test the two together. The software program extends the rev limiter to 7300 rpm and maximizes fuel and timing for maximum reliable horsepower with 91 octane. It also eliminates the 155-mph speed governor. I wasn't about to test that, so I'll just take evosport's word for it. Be sure whatever tires you use are rated for the speeds you drive, even if only on a racetrack.

Back on evosport's dyno, the car made 354.3 hp at 6700 rpm in fourth gear. Torque also rose from a baseline 333.7 lb-ft at 4550 rpm to 342.2 lb-ft at 4400 rpm.

evosport pulleys come in two different configurations: the "Audio kit" and the "Power kit." The difference between the two is that the Audio kit underdrives only one of the two tensioner pulleys, and the alternator pulley is slightly different. This way the Audio kit can be used with large sound systems that require a lot of power to operate.

The Power pulley kit consists of replacement pulleys for the alternator, power steering, water pump, crankshaft and both tensioner pulleys. A 64-in., seven-rib belt is supplied with the kit. Vadim said that evosport's Power pulley kit typically yields 6 to 8 hp by itself.

To help on the intake side, evosport supplied cleanable replacement air filter elements from K&N, which feature a million-mile warranty. There is another system, comprised of a full cold air intake, but that will be tested in "Phase 2" of this two-part article.

On the dyno, the pulleys and air filter elements increased the power by yet another 10 hp--364.5 hp at 6400 rpm with 343.7 lb-ft of twist to the wheels.

The gains over the previous run without the pulleys and filter elements were primarily in the top end, which is why the peak torque value remained almost unchanged. Still, it's the area between the two curves that counts, although the peak torque value didn't go up by much; 340 lb-ft of torque is now realized from 3500 to 4800 rpm.

Every upgrade tested here--including the exhaust, software, pulleys, air filter elements and a new set of spark plugs--makes up evosport's Stage 1 performance upgrade for the E39 M5. The entire kit retails for $3,799, and evosport can install it at its Huntington Beach facility for an additional $680, which covers the 8 hours required for installation. On this test vehicle, maximum gains over stock occurred at 6400 rpm, which gave the M5 a gain of 24.3 hp and a maximum torque gain of 20 lb-ft. And although peak gains happened past 6000 rpm, low-rpm gains included an 18 lb-ft gain at an early 2300 rpm.

The power gains are evident when driving the car. Let the clutch out, begin rolling in first gear and mash the throttle, and in a V8-torque instant the 275-section rear tires are screaming with traction loss. Since the greatest of the torque gains happened in the top end, a third gear rip from 80 to 100 mph was never as quick and smooth as it is now. This M5's V8 propels the car with a pounding fury through redline in every gear, with very little effort no matter what rpm you start at thanks to over 300 lb-ft of torque twisting the rear wheels from 2000 to nearly 6400 rpm.

Stay tuned for the second half--I'll hopefully unleash a few more ponies from this already magnificent BMW powerplant.