Turbocharger

At the heart of the K04 Turbocharger System is an APR proprietary customized version of the factory Borg Warner K04-64 turbocharger originally equipped on VAG’s high-output models, such as the Golf R and S3. The turbocharger features a CNC-machined, billet compressor wheel and stainless steel exhaust turbofold.

Each turbocharger unit is machined, assembled and clocked in house at APR with the necessary brackets to ensure proper wastegate fitment and orientation. Each wastegate is then calibrated for precise operation and control to ensure seamless integration with the expertly recalibrated OEM engine management system.

Integrated DV

One of the greatest benefits to the APR K04 turbocharger system is its simple, yet elegant design. APR's CNC-machined OEM compressor cover with integrated DV recirculation mount significantly reduces engine bay clutter and saves the end user from the hidden costs of purchasing extra throttle body pipes, hoses, clamps and DV mounts for recirculating boost pressure. The compact design also removes extra charge piping volume to allow for faster boost response and less locations for boost leaks. Furthermore, charge air pressure is directed directly at the compressor wheel which helps keep the turbo spooled upon lifting the throttle, minimizing turbo lag.

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Engine Management

The factory Bosch MED 17 engine management system is responsible for proper operation of the engine during constantly changing environmental and load conditions. With built in compensational data for environmental variables and varying load conditions, the factory ECU is far more complex and intelligent than units found in other vehicle makes and marques.

With the significant amount of changes included in the APR K04 Turbocharger System, APR’s Engineers spent months calibrating the engine management system, including hundreds of hours of in-house chassis dyno development. Drivability, gear changes, cruising and part throttle operation were tuned to operate smoothly as if intended by the OEM through proper torque management. APR’s Electrical Engineers built new coding functions, strategies and routines into the ECU to control conditions normally unseen at factory power levels. Thanks to APR’s incredible proprietary calibration suite, data logging software and full access to the coding structure of the ECU, appropriate and intelligent changes are made to ensure flawless drivability and excellent performance without compromise.

Engine Calibration:

APR’s Calibration Engineers restructured the engine’s volumetric efficiency (VE) model to correctly determine the ECU’s calculated load and deliver proper torque management. Thanks to APR’s patented boost control coding, the ECU is able to perform closed loop boost control well beyond relatively low limits dictated by the factory structure. This directly translates to safer and more predictable operation while additionally producing more power and torque across the entire power band.

Additionally, through the properly reconstructed VE model, accurate open loop fueling is achieved, translating to insignificant fuel trim adjustments.  Closed loop fueling is calibrated to control lambda perfectly under all operating conditions.    Furthermore, compensations, such as ones related to intake air temperature, exhaust temperature, and altitude, are adjusted to handle the larger variances compared to the factory, low-output setup.

APR’s Calibration Engineers have optimized cam timing, runner flaps, valve lift, ignition timing, engine load and lambda to provide tremendous leaps in power while retaining the OEM knock control strategy.

Compressor Surge Avoidance:

To aid in turbocharger reliability and longevity, APR’s engineers carefully studied the turbocharger’s compressor maps to avoid regions where compressor surge may be experienced. The K04 turbocharger has fantastic response characteristics and is able to produce incredibly high pressure at low airflow levels, but in doing so, the turbocharger runs into issues of compressor surge. In the area between 3000-4000 RPM, APR’s Calibration Experts have elected to limit boost pressure.

Torque Management and Traction Control:

Torque management plays a big role in how the vehicle feels and performs, especially during moments of low gear, rapid acceleration. Since APR’s torque management system relies on the engine management’s phenomenal torque reporting abilities, it is able to adjust to every environmental situation it encounters. To achieve a targeted torque level, the ECU applies the appropriate changes to mass airflow and ignition.

Acceleration Enhancements:

Through further calibration changes APR’s Calibration Engineers were able to increase the acceleration rate of the vehicle. Ignition delays are reduced resulting in a more responsive pedal without altering overall throttle sensitivity and resolution. Drivability was greatly improved by reducing the throttle lag commonly noticed at slow speeds and while reapplying throttle after decelerating. APR’s Motorsport Rev Limiter allows power to climb all the way to redline without dropping off several hundreds of RPM earlier. Lastly, APR’s tried and tested Motorsport Launch Limiter allows the driver to focus on launching the vehicle, rather than controlling the engine speed.

Part-Throttle Drivability:

Beyond wide-open throttle performance, APR’s Calibration Engineers spent countless hours optimizing vehicle drivability under daily, part-throttle, driving. The vehicle fully retains its impressive daily driver status and simply has more power on tap should the driver request more with his or her right foot!

APR EMCS and APR Mobile:

APR’s EMCS program-switching technology and APR Mobile put control of the ECU in the operator's hand to access modes for standard pump fuel, high-output race fuel and even reduced-output valet modes to protect the vehicle against improper use by other individuals. This technology is patented by APR and is found nowhere else in the world. It’s Performance Without Compromise only APR can deliver!

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Gaskets

APR doesn’t cut corners even with the most mundane details of the kit. Every nut, bolt, stud, washer, clamp, and gasket necessary for the install is included with the kit.

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