Basic Bolt-On Power for the BMW E39 M5: Part 2

To recap from the last time we tested this E39 BMW M5 (10/03), we realized sizeable gains from basic performance upgrades. With help from a pair of replacement air filters, a Supersprint cat-back exhaust with cross-over pipe, evosport power pulleys, Denso Iridium plugs and evosport software, the car climbed from an already strong 345 whp to an even stronger 365 whp. The entire evosport Stage1 package retails for $3,799, not including the $720 installation charge.

Meanwhile, I was waiting for the highly anticipated Supersprint headers and high-flow catalytic converters. Supersprint North America finally got its hands on the first set in the country and shipped it to us. We once again chose one of its largest distributors, evosport, for installation and testing, especially since evosport now uses these headers as part of its Stage 2 power package for the M5, which includes software.

The Supersprint headers are made from AISI 304 stainless steel and feature equal-length, four-into-one tubing. The individual primaries are also separate pieces for a much easier installation. Supersprint uses metallic cats, because they reportedly have a much better threshold under high heat situations when compared to the stock ceramics. These cats also much higher flow than the factory units, with 100 cpsi (cells per sq in.) versus 400 cpsi stock.

Before I get into the testing, realize that this exhaust system isn't cheap. At around $5,400 for both the headers and metallic cats--plus installation--it could burn a serious hole in some wallets. But, if you compare it to other exhaust systems available for the M5, it justifiably turns out to be a relative bargain.

The M5 was strapped onto evosport's Dynojet 248C chassis dyno. In order to get an E39 M5 to pull to redline without the ECU freaking and cutting out the power (it doesn't like to see mismatched wheel speeds), you have to pull the #17, #30 and #31 fuses.

As mentioned, the car made 345 whp with SAE correction, but I didn't think it would be a good idea to go on with this exhaust test and not get a new baseline run just prior to the installation. And without knowing how much the weather and air pressure differences would affect the results, it was something we had to do.

Our new baseline run was, remarkably, down to 350 whp with the SAE correction-down nearly 15 whp from the last time this car was tested with the evosport Stage 1 upgrade. For whatever reason, be it air density or temperature, the SAE correction was using a different factor for each run. Still, when both runs were compared uncorrected--which represents the horsepower actually put out on that dyno on that day--they were both at 363 whp. We knew everything was operating normally, but we decided to use the new baseline, since it would help represent true gains or losses from the headers today.

To get accurate readings, evosport hooked up a scanning tool to the car, which I monitored through a Sony Palm Pilot. This ensured that the aftermarket header system was tested under the same intake temperature and coolant temperature conditions, giving us realistic gains or losses.

Vadim put technician Steve Lee on the job. Since this was the first system in the country, this was a new experience for evosport. It turned out that the factory M5 headers actually called for the motor to be unbuttoned from the mounts and slightly raised with a tranny jack to slip the O.E. headers out. When all four pieces were removed, it was evident the car was going to need new factory exhaust header gaskets, which evosport supplied.

The inspection of the O.E. header system began, and to our surprise it seemed to be less than optimal for performance. First, the four runners on one side didn't even match the runners on the other. Some had individual primaries and some were collected--not what we expected. The Supersprint header, on the other hand, features equal-length tubing, and both sides collect with a 4-in-1 design. This system was already showing horsepower gains in the theory dept. alone. How much in reality?

The new system was installed and ready to go. Upon start-up, the car's once purring V8 was not a snarly growl. This time you could feel it in the seat of your pants. A blip of the throttle brought to life the much-improved throttle response, close to what driving in "sport" mode felt like before. And now with the new header-back system, the "sport" mode's throttle response makes it almost too difficult to drive!

When the car was again strapped to the dyno, we let it warm up to its normal operating temperature, and the actual temperature at which we previously tested: 174*F coolant and about 83*F air intake. When the car reached its targeted temperatures and with a roar from the new exhaust system, the wheels spun the rollers to near 140 mph, a fourth-gear pull. Right away the power went up to a whopping 374 whp. Although this gain was impressive, the new air/fuel ratios told the whole story--this car wasn't done making power. Previously, the baseline air/fuel ratio dipped into the upper 12s, but now the car was running way richer with the new headers, bringing the air/fuel reading down well into the 11s, too rich for a normally aspirated motor. evosport knew that more, reliable power was available.

Next evosport tweaked the ECU a bit and leaned out the mixture to where it was before, with the upper rev range back to the upper 12s. After a couple of hours of software tuning, evosport fixed the mixture throughout the entire rev range and managed to squeak out yet another 5.6 peak hp, bringing the total up to a catapulting 378 whp, again with properly monitored coolant and intake air temperatures. According to the Graphing Scanner, the engine was pulling through up to over 47.5 lb/min of air at redline, indicating roughly a 35-hp increase at the crank over our previous Stage 1 upgrade, which was flowing a 44 lb/min maximum.

The evosport Stage 2 upgrade for the E39 M5 proved to supply a 7% gain in horsepower over the Stage 1, which alone had about a 5% gain over stock. Bringing the two stages together and taking into account the corrected differences between baseline runs, the Stage 2 system--now comprised of the full Supersprint engine-back exhaust system featuring high-flow cats, replacement air filters, power pulleys and a remapped ECU--proved to be a 13.3% gain over stock.

"All right! Let's get this thing off the dyno already!" I yelled, trembling with anticipation. I couldn't wait any longer to drive it.

From my first rip in second gear, I could totally feel the difference. At about 5000 rpm, the car comes to life as if you just told all three of your 200-lb passengers to jump out the windows. Unless you plan to change the tires often, I'd take it easy in first gear. It's pretty much useless at wide-open throttle, and for the next couple hundred miles of testing, I found myself launching in second gear more times than not.

What do I think about the sound? Well, my wife, who has taken rides in numerous high-end performance cars, said, "Whoa, this one sounds like a race car!"

Besides the obvious power advantages of the Supersprint headers, the motor doesn't have to be raised to install this system, which should save in labor costs alone over a system that does require it. And whether or not other systems available can match the performance of the Supersprint, I do know Supersprint has built one kick-ass header system. It should be available as part of evosport's Stage 2 system by the time you read this. And good news for you E39 540i folks: The Supersprint header system will bolt on to your 4.4L V8, too!

If you wish to upgrade your bone-stock E39 M5 to evosport's full Stage 2 system all at once--which also includes everything in Stage 1--the price is $8,690, plus $1,300 installation. This includes evosport's dual-stage ceramic coating of the headers, worth $300, which wasn't available at the time of this test.