Supercharged Vs. Turbocharged
BMW E39 5 Series Shootout

By Pablo Mazlumian
Photography: Les Bidrawn

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.

The original gearbox was a five-speed automatic (Jimmy still regrets buying an automatic) with a 2.81:1 final drive in the open differential. The unit was swapped for a Dinan limited-slip differential for better traction, and acceleration was further enhanced with a 3:15:1 final drive. Additional Dinan software also controls the shift points to maximize power delivery.

The car is fast--very fast. A slight stab of the throttle and the 5er jumps forward with a menacing V8 growl that's reminiscent of a domestic muscle car. Hold the throttle down for a while, and the growl turns into a roar as you're propelled to speeds well beyond what any legislator would deem safe.

For initial testing the car was strapped to the Primedia Tech Center's Dynojet 248C dynamometer. A fourth-gear pull revealed a whopping 377 hp at the rear wheels at 6200 rpm, and a respectable 337 lb-ft of torque at 5070 rpm on 91-octane pump gas (stock E39 M5s peak at 340 whp on a Dynojet with SAE correction). That pull also made the car's speedometer reach well past 145 mph with a ferocious sweep of the dial.

Surprisingly enough, it was evident timing was being pulled back in the higher rpm range, indicating either very conservative knock retard software from Dinan or the motor not being able to make the power smoothly with 91 octane, or both. After repeated runs, the drop in torque and horsepower at that rev range grew worse, and we advised Jimmy to throw some high-octane fuel in the mix when he plans to drive the car hard, especially in summer heat.

The 532i
When Charles Yeh picked up his new 528i automatic, neither he nor the dealership had an inkling about the transformation this car would undergo over the next couple of years.

As it was with Jimmy Wu, Charles also regretted buying an automatic. Instead of selling it and picking up another BMW, though, he sent his car to Michael Angelo Motorsports, where it underwent serious surgery and was modified with a five-speed manual transmission. The 2.8-liter six also was pulled and replaced by an E36 M3 3.2-liter motor augmented by an RMS blower. Charles wanted still more power and so shipped the car east, where the BMW turbo nuts at Active Autowerke got their hands on it.

If you've been following Project M3, you've no doubt read about our enthusiasm for Active Autowerke's turbo system. However, Wu's 532i was taken a step further and received a freshly built, low-compression motor with dished JE 8.5:1 forged pistons and Pauter connecting rods. Then AA fitted its Stage 4 turbo system, featuring a Garrett T-61 turbocharger, a 4-in.-thick intercooler capable of flowing 1450 cfm, AA turbo-spec camshafts and signature exhaust manifold. Other components included 55-lb/hr injectors, custom software, custom cold-air intake, bigger fuel pump, custom fuel rail, external fuel pressure regulator, external wastegate and an electronic boost controller. Exhaust gases run through AA high-flow catalytic converters and a Stromung muffler.

Interior accessories of note are a Z8 factory engine-start button, a VDO boost gauge mounted flush to the A-pillar, and a steering-wheel-mounted Greddy boost toggle switch.

Since the turbo sits so low, a Tilton oil pump on the oil return line pumps the slick stuff from the turbocharger back to the pan. An HKS Twin Power DLI ignition boost system keeps the spark alive under high boost pressures. Most of the turbo system's components, including its plumbing, are protected by AA's aramid wraps, keeping the heat in the engine compartment at a minimum. Power is transferred to the tranny through an AA four-puck high-performance clutch system with a 12-lb flywheel. From the 5-speed, the torque continues to a 3.15:1 differential from a Euro-spec M5.

To keep intake temperatures as cool as possible and help prevent detonation, an AA/Aquamist water and alcohol injection system was installed. It uses dual accumulators feeding two 0.9mm nozzles to spray a fine mist of water and alcohol into the intake elbow right before the throttle body.

Braking is crucial in a car with so much power, so it was also fitted with Brembo's 14-in., four-pot system in the front. However, the rears use factory calipers with Brembo cross-drilled rotors. To help keep the car firmly planted, Wu installed Koni adjustable dampers and H&R Sport springs and an AC Schnitzer strut tower bar.

Aesthetically, the car sports a tasteful M-Technic body kit, pretty much the same look found on the M5. BBS Le Mans wheels widen the car's footprint with 8.5x19-in and 10.0x19-in wheels wrapped with Bridgestone S-03 performance radials, size 245/35-19 front and 275/30-19 rear. Hella xenon headlamps, fitted with Phillips 6000k xenon bulbs, light up the road and allow Wu's foward vision at night to keep up with the car's progress.

My fingers were twitching in anticipation of the T-61 turbo's rush. From a second-gear roll at about 30 mph, I mashed the pedal to the floor and awakened 19 psi of boost. The turbo didn't whine or whoosh--it growled! To drive a car this big and heavy that was this fast was a unique thrill. Reaching third gear was almost immediately followed by triple digits on the speedometer, and the roller-coaster effect made my stomach drop to the bottom of my abdomen and had me thinking the car was absolutely dangerous.

There was one major problem, however--the 532's top speed is governed to just 112 mph. It's believed that some of the electrical hardware involved in the E39 is not compatible with the new drivetrain, or something was overlooked during the car's conversion to manual shifting. Needless to say, even Charles has yet to experience a full-boost run in fourth gear. Maybe that's a good thing....

Because of this, the car had to be dynoed in third gear, since fourth wouldn't allow a run to redline. The car made a very clean run on 91-octane pump gas, spinning the drums quickly enough to yield a jaw-dropping 400 hp at the wheels at 14 psi. With a few gallons of Sunoco 104 fuel added to the mix, we tried a run in the high-boost mode. On the dyno the turbo wouldn't see more than 18 psi, but it was still good enough for a heart-stopping 447 bhp at the wheels. At this point we realized maybe this wasn't going to be a fair test, but the 532i would still have that top-speed governor to contend with.

The Test
It was time to put the cars to the test: a supercharged V8 versus a turbocharged inline six, competing at California Speedway in Fontana.

The 540 was up first. Although Jimmy told us he'd achieved 12.7s on slicks, we wanted to see a street versus street setup, which meant street tires only.

With its instant V8 supercharged torque, we figured any advantages would be seen off the line, but having an automatic transmission didn't help much. Our test driver added a little power braking to give the car the extra wheel slip it needed. Once the wheels gripped, the car took off with a vengeance, the rumble of the V8 echoing off the walls the entire way down the strip. After a handful of passes, the best two averaged out to a 13.3 at 107.6 mph--very impressive considering the 1,200-ft elevation.

Next up was the 532i. Our test driver had his hands full getting it off the line cleanly with its grabby quad-puck clutch and tire smoking torque. Remembering to switch the boost toggle switch from low to high boost in third gear required additional concentration.

The car was lined up, revs were raised, and the clutch was released--ok, sedans aren't supposed to do what we just saw. First gear was complete smoke, but when second gear was engaged it was off like a rocket. The sound? Imagine packing so much air through an exhaust that it wants to just explode--that's what it sounded like.

Just as we expected, the car hit its 112-mph speed governor about 150 ft before crossing the finish line in each run, forcing it to coast the last full second of the quarter mile. Even so, the car still saw sub 13-sec. runs, averaging out to 12.9 at 105.4 mph.

Off the line, both cars took off in different manners but posted similar acceleration numbers to 30- and 60 mph. Once the 532i got its traction, however, it was lights out for the 540 (as it would be for nearly every car on the road), with a 70-110-mph blast in just 5.5 sec.--two full sec. faster than the 540.

It was unfortunate we didn't find a blown 540i with a six-speed manual transmission near us--chances are it could have achieved that high-12-sec. mark. Equally as unfortunate, however, was the 532i's speed limiter. But as far as we know, there was no other setup like this in a 5er at the time. Had it a fourth gear that could see over 5000 rpm, the 532i probably would have seen mid 12s at speeds between 116-118 mph. Still, its motor packed enough juice to coast it to the finish line first that day.

 

Terrible torque curve by the turbo car. Totally unusable for every day driving.

 

holy crap that 532 is fast.

 

Damn that sux that he can't remove the limiter.

 

i like that 528i very nice IMO

 

Damn that 532 took out the 540? Very sweet.

 

what a waste for the 3.2 turbo. Imagine racing him from 80 past 100 yeah he would beat you till 112 then your $30,000 acura will walk right by him.

 

A few problems with these cars. 1. Somebody needs to teach them how to detail. The swirls on those cars are horrible. 2. Gavril is right, the torque curve sucks. 3. Speed limited to 112? I took my modded Civic Si way past that.