The debut of the 3.0-liter, twin-turbocharged, six-cylinder engine in the 2007 335i heralds a new generation of BMW turbos. It is now feasible to build a motor with the horsepower and torque of a V8, while still achieving the fuel economy of a standard six. It also means it's time to play. We tracked down a 335i sedan to put a few upgrades to the test.

*Baseline
Peak wheel-hp: 254 @ 5588 rpm
Peak wheel torque (lb-ft): 255 @ 2144 rpm

*Pros
Engine has long torque curve Twin turbos for quick spool-up Direct injection technology Front-mounted intercooler

*Cons
Each turbo features a pair of restrictive catalytic converters, one directly off the turbo, the second downstream.Diverter valves are integrated

*Notes
The 335i sedan was equipped with a six-speed automatic transmission with its odometer reading 1232 miles at the start of testing. The vehicle was tested using the highest grade of gas available in Southern California: 91-octane. All testing and installation was performed on the same day, during moderate temperatures of 77 to 79 degrees F. The testing location was at sea level with a reading of 46 percent relative humidity.

All dynamometer testing was performed in third gear on a Clayton 'Mustang' dyno.

Split Second Turbo Tuner upgrade
Peak wheel-hp 270 @ 5623 rpm
Peak wheel torque (lb-ft) 277 @ 2227 rpm

*Pros
Plug-and-play design allows for easy install and removal when going in for dealer service Retains the smooth power curve OEM plug housings ensure perfect water-tight fit Built-in temperature compensator reduces boost based on temperature

*Cons
Relies on the engine control unit (ECU) to adjust air-to-fuel ratio No speed limiter removal Rev limiter not increased

*Part: Tuning box

*Tools: Small flathead screwdriver

*Price: $599

*Installation time: 5 min.

*Notes
The Split Second Turbo Tuner is a reasonably priced option to increase horsepower and torque output, and the fact that it can be removed easily makes servicing at the dealer less stressful. The Turbo Tuner is installed between the ECU and the TMAP sensor, providing a mild increase in boost pressure. Performance gains are not limited to any specific part of the rev range; they can be felt throughout without a single hiccup. The increased power does not adversely affect the automatic transmission.

Super Sprint Cat-Back Exhaust
Peak wheel-hp 279 @ 5691 rpm
Peak wheel torque (lb-ft) 285 @ 2301 rpm

*Pros
Mid-pipes feature an X section, ensuring that the equalization of exhaust gas pulses is optimized60mm mandrel bent tubing 100 percent T304 stainless steel Uses all factory hangers No reduction in ground clearance100mm tips fill the bumper cut-out

*Cons
Adjustable tips are a bit tricky to get lined up Requires cutting of stock one-piece exhaust right after the stock catalytic converters

*Parts: X-pipe, right and left muffler and tips, clamps, muffler cross brace with hardware

*Tools: WD40, T50 Torx socket, long flathead screwdriver, 16 and 17 mm deep socket, three-inch extension, ratchet, 6mm Allen wrench, 12mm wrench, chop saw or Sawzall

*Price: $2,362.91

*Installation time: 60 min.

*Notes
The stock exhaust sounds good only when completely floored, thanks to the vacuum-operated flapper. The Supersprint exhaust system gives the 335i more presence, offering a range of tones from a mild idle to aggressive full throttle. If cutting the stock exhaust system is not an option, Supersprint offers two alternatives (that are not quite legal, because they replace or remove two of the four factory catalytic converters): a set of front connecting pipes with two 100-cell HJS cats ($3,211.87) or a set of front connecting pipes with no cats ($551.83). With either option, the system will bolt right to the factory downpipes. If future plans are to install a set of downpipes, the front connecting pipes with cats feature O2 sensor bungs, allowing relocation of the sensors to avoid a 'check engine' light.

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