Excessive Force

With 817 rear-wheel horsepower, Robert Henning’s HPF Stage 3 turbocharged E46 M3 represents overkill in its most absurd form imaginable…and it’s amazing.

Photo: Excessive Force 1
August 24, 2010

Mission creep.

It’s a phrase used by the military to describe operations that gradually increase in scope until they go way beyond their original intent. It’s a phrase that can also describe the evolution of many a project car.

Take the 2004 E46 M3 owned by young Southern California enthusiast Robert Henning. When he first decided to tune the car for more performance, he envisioned only a few upgrades.

“I think the first real modification was a CSL-style carbon fiber rear diffuser,” he recalls. “I was looking into full exhaust and pulley packages after that, but the price was almost as much as a supercharger.”

It was enough to make Henning consider his alternatives. Doing a bit of casual exploration, Henning came across a company in the Pacific Northwest called HPF, which stands for the self-explanatory Horsepower Freaks. Intrigued by HPF’s turbocharging kits, Henning decided to skip the piecemeal mods altogether.

Photo: Excessive Force 2

“One day, I just decided to save my money a little longer,” he says.

And thus the mission began to creep.

Big power and a bulletproof motor

This is Henning’s second M3. Although the first ended its days in a traffic accident, he liked it enough that he bought another one soon afterwards.

“I love everything about the E46 M3,” he admits. “I think it is one of the best M3s ever made. It looks amazing next to brand-new cars and has a timeless body style. A stock M3, if put into the hands of the right drivers, can do wonders around a track. It’s just an all-around amazing car any way you look at it.”

As much as Henning appreciates the M3 in stock form, he also was drawn to its ease of modification, and by the big improvements offered by companies like Horsepower Freaks.

Photo: Excessive Force 3

“I decided to go with HPF after watching all the videos from them on YouTube and talking to HPF,” he says. “I wanted to have something different, and at the time not too many HPF cars were on the road.”

In a sea of supercharged M3s, Henning figured a turbocharger would be the ticket to individuality. Before long, his M3 was being poked, prodded and reconfigured for big power by HPF’s technicians, who began by removing the S54 engine and completely disassembling it to make sure it could cope with the awesome power made possible by the turbo.

HPF’s Chris Bergemann claims that the engines his company builds are “bulletproof,” and the work that goes into each one certainly suggests as much.

The original crankshaft is left completely stock, but the connecting rods are replaced by HPF’s proprietary rods, which have been specifically made for this rigorous application. The rods in turn actuate custom forged pistons with ceramic-coated skirts and radiused edges (rather than the sharp edges they have when forged) to eliminate hot spots and reduce the chance of heat damage. The rods and pistons are mated with thicker custom wrist pins.

Before everything is buttoned up, each cylinder in the block is machined to the measurements of the actual piston that it will hold, ensuring exact tolerances. Atop the block, the S54 cylinder head is left completely untouched and uses all stock parts, though it’s now fastened to the block with ARP L19 head studs.

Photo: Excessive Force 4

“The standard ARPs literally stretch under the extreme cylinder pressures,” says Bergemann, “so we had to go with their L19s, which have a tensile strength of 260,000 psi.”

Keeping it cool throughout

On the fuel side of the equation, the M3’s stock single fuel pump is joined by two Walbro 255 pumps mounted under the driver’s side of the car. HPF also installs an additional fuel line from the tank to the fuel rail. The stock fuel injectors are replaced with low-impedance 1,200cc fuel injectors that reduce the 73-psi factory fuel pressure rating to 40 psi. Under maximum boost, the fuel pressure rises to around 65 psi. Basically, the point is to get more fuel to the engine with less pressure. An AEM fuel injector driver box controls the fuel system.

A single Precision 71mm turbocharger provides forced induction. The turbo features dual ball bearings and a billet aluminum turbine wheel that’s been CNC machined rather than cast for light weight and optimum vane geometry.

“This turbo actually outspools some smaller turbos,” Bergemann says, adding that machining also allows different configurations to be designed very quickly, speeding up the development process.

Since HPF locates the turbocharger below the oil pan, an oil scavenging pump is installed to recirculate engine oil to the turbo housing. The turbo is also liquid-cooled by the BMW’s cooling system. A massive intercooler is mounted up front, and oncoming air is routed through HPF’s proprietary intake manifold. The latter is designed to work with methanol injection, which cools the intake air for an instant power boost when activated by a controller in the cockpit.

Photo: Excessive Force 5

“We’re the first company to run 100% methanol,” says Bergemann, noting that most cars that run this type of setup use a mixture of 50% methanol/50% water (or a similar ratio) pumped into the intake tract.

The M3’s electronics have also been subjected to HPF’s black magic A piggyback ECU controls the factory DME, and a knock-sensing alarm emits an ear-splitting tone if the engine is running too lean and is about to suffer permanent damage to its internal organs.

The results of HPF’s efforts speak for themselves. According to Bergemann, this Stage 3 M3 pumps out 635 rear-wheel horsepower when running 17 psi of boost and using 91-octane pump gas. Pump up the boost to 23 psi, flip the switch that brings methanol injection to the party and power leaps to 766 rwhp. Fill the tank with race fuel and power grows to 768 rwhp, while race fuel and methanol injection allow the power to swell to a staggering 817 rwhp. Do the math and that’s only a few horsepower shy of 1,000 crankshaft horsepower…from an engine that originally put out 333 crank hp, and which HPF claims is still perfectly suitable for ordinary street driving.

In order to safely harness it all, HPF also engineered a traction control system that limits the amount of available power based on the speed of the vehicle. The faster the car is traveling, the more power the system feeds to the rear wheels, resulting in a BMW that accelerates fastest when headed towards triple digits, since full boost isn’t available until over 80 mph. It further has settings for Race, Sport, Street and Rain.

Speak loudly, carry a small stick

In person, Henning’s car is the epitome of understatement. Actually, that’s not entirely correct, since I hear the M3 rumbling up the street in Pasadena long before I see it. The aural signature that spills from the 4.0-inch diameter HPF exhaust of this M3 has more in common with that of a full-fledged competition car than one that is purportedly street legal.

Photo: Excessive Force 6

Once we’ve retired to a deserted brick alley for our photo shoot, Henning switches the motor off, at which point all suggestion of the car’s immense power disappears behind its smooth, silver flanks. The stock-looking bodywork makes a nice change from the wide-body HPF cars we’ve become accustomed to seeing.

Though it lacks bulging fenders and impossibly wide rims, the exterior of Henning’s car isn’t entirely devoid of upgrades. It’s wearing a vented hood in carbon fiber from Asuka, plus a carbon fiber trunk lid, front bumper and rear diffuser from Vorsteiner. Complementing the understated exterior are the excellent BBS LM two-piece alloys that measure 8.5 × 19 inches up front and 9.5 × 19 inches at the back. The wheels have been shod with 235/35ZR-19 Nitto NT05s at the front and 275/30ZR-19 Toyo Proxes R888s at the rear.

Inside, the stock M3 chairs have been exchanged for a set of deeply bolstered one-piece Recaro Pole Positions trimmed in leather. The rest of the interior is stock, save for a smattering of gauges and knobs that monitor the health of the engine and control the various turbo-related functions.

The stock suspension has been swapped for more performance-oriented KW Variant II coilovers. They’re certainly on the firm side, but they imbue the M3 with a more nimble chassis, plenty of grip and very keen turn-in from those big 19-inch front wheels. On the stopping end of things is a Rotora big brake kit with six-piston calipers at the front and four-piston calipers at the rear.

As impressive as they may be, we’re not here to see no stinkin’ suspension and brake upgrades. No, the hook here is horsepower, and lots of it.

Photo: Excessive Force 7

Driven in traffic at a moderate pace, this M3 feels as stock as it looks. With the exception of the exhaust—which, to be honest, I find embarrassingly loud—this could be an ordinary, mildly modified M3. That, however, is only the beginning.

“It steps sideways pretty quick when you get on it,” says Henning casually from the passenger seat as I steer the BMW onto the freeway—not exactly the most comforting words even though the engine is “only” putting out about 650 rwhp at the moment.

Accelerating onto the on-ramp, I press the gas pedal to the floor and the M3 rockets forward. With all that power available with a twitch of my right foot, acceleration is extremely strong. The BMW lunges forward with a loud shriek from the exhaust and a whistle from the turbo as it spools up, followed by the spitting of the wastegate at each upshift through the SMG transmission.

Sense-scrambling acceleration

Once I’ve become slightly familiar with the acceleration, Henning flicks a switch to let the engine make its full 768 horsepower, the most that are available on the pump gas we’re running today.

As the gas pedal heads to the floor, the M3 takes on a demented level of acceleration that is sense-scrambling in its immediacy. As if by instinct, my right hand pulls the SMG paddle for an upshift before the engine has even revved past 6,000 rpm, far short of redline. I haven’t really let this thing rip yet, but OM*G! (I’ll let you fill in the missing letter.)

It takes a few runs through the gears to become accustomed to the absolutely ferocious acceleration. It’s so intense that a “fight or flight” instinct kicks in somewhere in my brain’s limbic system. My right foot wants to lift, to make the car slow down as I’m forcefully pinned back in my seat, but another part of me wants to keep the throttle wide open.

Blasts of acceleration become an exercise in compressing distance. Eye a half-mile opening in traffic, sink the gas pedal to the floor and haaaang on. The rear tires scramble for traction and eventually find it, while the unmuffled, metallic shriek of the S54 is punctuated by the shpitt! of the blowoff valve at every upshift.

It’s invigorating but not entirely comfortable, and frankly I’m glad to get out of this car without having been sent to jail. I’m not sure I entirely see the point of a BMW with this much power, but it’s probably similar to Mount Everest. People climb it because they can, and that’s why Henning owns this car: Because he can.

So here’s to mission creep. Long may it bring us cars like this HPF Stage 3 M3.

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