This month, we focus on Volkswagen's 2.5-liter engine.We took a 2007 Rabbit 2.5 five-speed manual and started with the most popular and basic upgrades available. We added a chip, intake and exhaust, and looked to see how much horsepower and torque we could gain in the real world.

Baseline:Peak wheel-hp 138 @ 5100 rpmPeak wheel-torque (lb-ft) 144 @ 4000 rpm

Pros:Affordable Engine has long torque curve Handles well Electromechanical steering reduces torque steer

Cons:Low-range power peaks at 5100 rpmMotor feels flatRestrictive catalytic converter

Notes:The odometer read 1532 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 performed on the same day, during moderate temperatures of 74 to 76 degrees F. Testing location was at sea level with a reading of 46 percent relative humidity. All dynamometer testing performed in third gear on a Clayton(Mustang) chassis dyno.

Neuspeed EngineManagement UpgradePeak wheel-hp 143 @ 5100 rpmPeak wheel-torque (lb-ft) 158 @ 3600 rpm

Pros:Increases throttle responseUndetectable by the dealerIncreases rev limiter ceiling Free lifetime upgrades and free re-flash back to stock programming100 percent compatible with all diagnostic software

Cons:No additional gadgets (hand-held controllers, etc.)

Parts: None, software programming only

Tools: Laptop and Neuspeed OptiCan programming box

Price: $299

Installation time: 45 minutes

Notes:When upgrading software on a naturally aspirated engine, horsepower and torque gains are minimal and highly dependant on octane. Dyno tests were performed on 91-octane, a higher octane would have seen greater gains. The noticeable differences when driving is greater throttle response and smoother power curve.

Evolution TuningEvoair IntakePeak wheel-hp 148 @ 5100 rpmPeak wheel-torque (lb-ft) 160 @ 3500 rpm

Pros:Re-usable K&N Xstream air flow top cotton air filter with built-in velocity stack for optimal flow Billet EGR and air pump fittings 16-gauge steel heat shield/mass air flow sensor bracket mounted in factory rubber isolator Custom-molded four-ply silicon intake hose, allowing for precise fit and flexibility

Cons:Filter is heavy and close to headlamp

Tools:5mm Allen, T20 Torx screwdriver, Phillips screwdriver, flat-head screwdriver, pliers, 5/16, 1/4 and 10mm socket, ratchet

Price: $324.99

Installation time: 30 minutes

Notes:Use of a silicon hose from the throttle body to the mass airflow sensor (MAF) sets this intake apart. The molded hose allows for the placement of the MAF in such a way that it does not stretch the wires. The bracket/heat shield fits perfectly and even has a cut-out for the MAF sensor plug harness. The intake sounded amazing. Horsepower and torque gains are average for a naturally aspirated VW engine, but one notable item is the elimination of dips in the power curve.

Techtonics Tuning 2.5-inch exhaustPeak wheel-hp 150 @ 5100 rpmPeak wheel-torque 163 @ 3750 rpm

Pros:T-304 stainless steel piping Exudes deep tones Twin Borla muffler set-upTwin tips give an aesthetic improvement

Cons:Slip-joint construction requires considerable tweaking to get everything lined upOnce muffler clamps are tightened, the system is difficult to remove or adjust

Parts: Center pipe, front and rear muffler assembly, sealant, 2.5-inch clamp, double hanger clamp, three-pound damper weight, hanger retaining clamps

Tools: 13mm, 14mm, and 16mm sockets, ratchet, long flat-head screw driver, WD-40

Price: $765

Installation time: 1 hour

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