M-POWERING THE 3 SERIES
Raiding the M-brand parts bin and tweaking the turbochargers turns HP Autowerks' 335i Sedan into a sports car to beat the M3.
Ever since the days of the E30, BMW enthusiasts have been improving the standard 3 Series with parts from M cars. While some go so far as to swap everything from the engine to the interior for its M counterpart, most opt merely to improve the standard cars chassis with lighter, more sport-oriented M parts, gaining performance without sacrificing the stealth factoror the lower insurance premiumsof an ordinary 3 Series.
That venerable tradition has continued with the current generation of 3s, especially the 335i models. The turbocharged N54 engine makes these cars nearly as fast as a previous-generation E46 M3 right out of the box, and its easy tunability allows a 335i to rival even a current E90/E92 M3 without the hassle and expense of engine swaps or supercharger installations. And with its super-stiff and sophisticated chassis, the 335i is a capable sports car even before modificationafter a little help from M or the aftermarket, it becomes a supremely capable one.
Harold Lin already knew that when he and his business partner Peter van Wingerden picked up a new 2007 335i Sedan from the Santa Barbara Auto Group. The owners of HP Autowerks in Santa Barbara, they wanted to transform their 335i into a dedicated track machine that would rival the M3 for performance for far less money.
The 335i has a much lower sticker price than the M3, and that leaves plenty of money on the table for modifications, Lin told us. In addition to the lower pricing, it comes with a twin-turbocharged in-line six cylinder engine, which has a great potential for tuning.
To reach his goal of having M3-like acceleration and cornering power with a civilized ride for everyday use, Lin first installed shorter, stiffer springs and more performance-oriented shocks, which improved handling but not to the extent that HP wanted. Then, last summer, Lin had a flash of inspiration when the shop started working on a few of the new E92 M3s brought in by their customers.
We had an M3 up on the lift, so we put the 335i up next to it and started looking at the suspensions of the two cars, says Lin. A close inspection revealed that the suspension from the M3 would bolt onto the 335i without any issues, so Lin called the local dealer and ordered a complete M3 suspension, front and rear.
When the big brown truck arrives, the fun begins
When the UPS truck arrived, HP fitted the front end of the 335i with the tension rods, lower wishbones and strut tower brace sourced from the M3 parts book. At the rear, he installed M3 rear guide rods, upper and lower camber links and spherical subframe bushings. Lin also installed a set of hollow M3 anti-roll bars in place of the solid 335i anti-roll bars. The front M3 bar has the same 26.5mm outer diameter as the 335i bar, but its diameter is uniform throughout its length, without the tapered center section that reduces rigidity on the 335i part; it also uses a metal/rubber center bushing rather than the all-rubber bushing thats standard to the 335i, again for more rigidity. The rear M3 bar is also far more rigid than the 335i part, measuring 20mm in diameter instead of just 13mm.
Rather than fit the standard M3 shocks, HP installed a set of Koni double-adjustable shocks and Swift springs, which use smaller helper springs inside the larger main coils to push the suspension down during cornering, thus making sure that the inside wheels remain in contact with the ground. Aggressive cornering is aided on the other side of each axle by thrust sheets made from carbon fiber and aluminum; installed between the springs and perches, they allow the springs to rotate, thereby preventing binding and a temporary increase in spring rate. TC Kline camber plates and a Hotchkis rear chassis brace round out the improvements.
Even on double-adjustable Konis and very high-rate springs, the ride is firm but nowhere near harsh, perhaps even better than it came from BMW, says Lin. Understeer, which was built in from the factory, has been greatly reduced with proper spring rates and anti-roll bar selection.
Although BMWs original equipment brakes have improved of late, theres still room for an upgrade in that department, particularly on cars that will see track duty. HP opted for a StopTech kit that uses 355mm front rotors clamped by six-piston calipers and 345mm rear rotors clamped by four-piston calipers. For street use, Lin runs Performance Friction pads; on the track, he swaps these for Hawk DTC-70 pads at the front and Hawk DTC-60-pads at the rear. The DTC-60 pads on the rear have less initial bite, which helps prevent excessive oversteer when trail-braking into a corner.
The brakes may be oversized, but the wheels and tires are not. Theres no reason to go bigger than 18s, Lin says. On the street, the car rolls on Forgeline ZX3 alloys that measure 9.0 x 18 inches up front and 10.0 x 18 inches at the back, shod with 245/40-18 and 275/35-18 Nitto NT05s. For the track, Lin mounts D-Force alloys that measure 9.5 x 18 inches at all four corners, mounted with 265/35-18 Michelin Pilot Sport Cup tires.
In the engine bay, the twin-turbocharged N54 six is plenty powerful straight from the factory: On the dyno, HPs example delivered 248 horsepower and 277 lb-ft of torque to the rear wheels. Nonetheless, the shop wanted to bring its performance closer to M3 levels, so a few modifications were in order.
First, the ECU was re-flashed with LET Motorsports Stage X software. Next, an aFe Dual Cone Intake took the place of the stock airbox and a more efficient Code3 Performance/Spearco intercooler replaced the original inside the front bumper. Atop the turbochargers, a Forge Motorsports Diverter Valve kit was installed to evacuate excess pressure from the turbos back into the engine; its almost identical to the BMW valve, but Forge claims better reliability, particularly in modified vehicles. Finally, the stock exhaust was replaced by Berk Technologys 3.0-inch downpipes that lead into a Borla 2.5-inch stainless steel exhaust with dual mufflers.
On the HP dyno, the modified 335i put out 354 horsepower and 377 lb-ft of torque at the rear wheels, a 106 hp/100 lb-ft improvement that makes this 335i more than a match for an S65 V8-powered M3. (At the crank, the S65 makes 414 hp and 295 lb-ft, which equates to around 352 hp and 251 lb-ft at the rear wheels once driveline losses are taken into account.)
Despite the dramatic improvement underneath, HP chose to speak softly but carry a big stick where the 335s exterior is concerned. The car was fitted with a factory M-Sport body kitwhich in this writers view is all an E90 3 Series needsplus a 3-D front lower spoiler lip, APR splitter and one of Vorsteiners increasingly ubiquitous vented hoods.
Inside, the HP 335is track orientation reveals itself in a pair of grippy, one-piece Recaro Pole Position race buckets. Reupholstered in leather with Alcantara inserts set off by white stitching, theyre gorgeous but a pain to get into. An M-Sport steering wheel, shift knob and emergency brake handle complete the cockpit changes.
Untapped potential
in an already-fast 335i
Once we squeeze into the drivers seat, a prod of the Start button brings the engine to life with a muted burble. Its louder and more purposeful than stock, but the volume isnt out of place on a street car. As expected, this 335i is extremely quick in a straight line, and its twin turbos exhibit about zero lag as they spool up.
In any gear, tipping into the throttle produces instantaneous, neck-straining acceleration; if I didnt know about the two turbos hiding in the engine bay, Id swear this car had a big-displacement, normally aspirated powerplant under its carbon fiber hood.
The 335i launches down straights, pushing us hard into the seat as it rushes forward. The abundant mid-range power lets us shift well before redline and still set a blazing pace, though its quickly apparent that were getting nowhere near this BMWs outer limits of performance on the twisty canyon road were using as a test track.
On the other hand, the road is perfect for testing the sedans handling, which is equally if not more impressive than its prodigious power. The car stays absolutely planted through corners, with almost no body roll. As Lin says, the Koni suspension has perfect damping: Its firm without being jarring, and it offers enough feedback to let us know whats going on between the tires and the road at all times.
This sedan lives to go around corners, and it rotates quickly as we steer it through turn after turn. Gone is the annoying understeer that one encounters in a stock 335i, replaced by neutral handling. Turn-in is immediate, and the chassis feels far more nimble than stock.
Thanks to the instant hit of power from the motor, modulating the back tires is childs play, too, making handling not only neutral but safe and controllable, with oversteer easily accessible. Going into corners, the StopTech brakes are truly impressive, with immediate deceleration that feels as though a giant anchor has suddenly been deployed from the rear trunk.
All of that suggests a car that would be even more fun on the race track than it is on the street, and it makes sense that Lin has tracked it at California Speedway, Willow Springs, Buttonwillow, Laguna Seca, Infineon and even Spring Mountain in Nevada. Needless to say, he hasnt been disappointed on any of those tracks, nor on the drive to and from his home base in Santa Barbara.
As it is now, its great. The suspension tuning is near-perfect and it has more than enough power, he says. We have not only achieved the same horsepower output as the M3 with bolt-on parts and software tuning, we exceeded the M3s torque rating by at least 100 lb-ft, and that torque comes in at around 2,000 rpm. It almost doesnt matter which gear you are in, the torque can pull the car out of any turn with authority.
As good as this 335i already is, Lin sees plenty of potential yet to be tapped. The 335i tuning market is still in its early stages, so more horsepower and torque will surface in the near future, he says. Some tuners are putting down 400-plus rear-wheel horsepower with the stock turbos and internals. With a set of higher-flow turbos and beefed-up internals, I can imagine that 500 to 600 rear-wheel horsepower is near.
From the sound of his voice, Lin would have no problem with that whatsoever, and neither would we. If HP Autowerks can up the power without losing this 335is subtle appearance and neutral handling, we say go for it.
[bimmer-mag]
