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 Adapter

One of the greatest benefits to the APR K04 turbocharger system is its simple, yet elegant design. APR's CNC-machined direct compressor recirculation port on the OEM compressor cover 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.

Turbo Outlet and Turbo Muffler Removal

The OEM k04 turbocharger features a turbo muffler designed to reduce turbocharger sound, but does so at the cost of ultimate performance. APR removes the turbo muffler not only to enhance the sound of the turbocharger, but to also provide a smooth airflow path across the previously baffled muffler section. A clean and simple CNC flange developed by APR's Mechanical Engineers is bolted directly to the compressor cover in place of the OEM turbo muffler. A long mounting surface provides an excellent slip-proof surface for mounting the included APR EZ-Flow silicone discharge hose and an o-ring between the flanges ensures a life of leak-proof operation.

PCV Blockoff Plate

The K04 turbocharger was originally designed for an EA113 2.0T engine, and as such, includes items not present on the EA888 2.0T engine. The compressor cover features a port used in the EA113’s PCV system, but on the EA888’s this same port is located higher up on the intake tubing. APR has provided a gasket-sealed laser-cut port cover to block off this part to ensure no unmetered air enters into the system. The design is clean and simple and never requires maintenance.

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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. Further development was performed putting the vehicle through performance evaluation and durability testing at the drag strip and road course. 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 and the addition of a 3-Bar MAP sensor, the ECU is able to perform closed loop boost control well beyond relatively low limits dictated by the factory MAP sensor. 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, ignition timing, engine load and lambda to provide tremendous leaps in power while retaining the OEM knock control strategy. The result is safely achieved power, optimized for various fuel grades found around the world from low-quality pump fuel, all the way to high-quality, oxygenated race fuels.

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. During testing, with the limits removed, APR’s engineers were able to easily achieve over 400 ft-lbs of torque with 93 octane fuel, but doing so could result in damaging the turbo’s reliability. Back-to-back testing was conducted with and without the limitation and despite the reduction in torque in this range, APR’s engineers were unable to record a measureable difference in accelerative performance.

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. Typically front wheel drive vehicles suffer from excessive wheel spin during these moments due to the massive torque on tap from the K04 Turbocharger System. Some drivers can find themselves in situations where they are fighting against wheel spin and traction control when they are simply interested in going forward as quickly as possible. This is further compounded by the fact that the factory traction control (ASR) system was designed for vehicles producing far less power and torque, resulting in overcompensated ASR interventions.

APR’s Calibration Engineers set out to perfect torque management and traction control by minimizing wheel spin as much as possible without neutering the driving experience. A multi-step approach was taken to achieve appropriate control. With ASR enabled, forward movement wheel spin will trigger appropriate torque intervention levels to minimize spin without hurting forward acceleration. On top of this, the torque management system is fine tuned to deliver only as much torque as the tires can take. In normal conditions the tires will only slightly break loose under full acceleration, resulting maximum acceleration. In higher traction situations, or with ASR disabled, all of the system’s torque is directly on tap!

While the end goal is similar, APR’s torque management system differs greatly from archaic “boost-by-gear” strategies. “Boost-by-gear” strategies rely on a static limitation of boost in an effort to minimize wheel spin, but to work properly they must be dialed in for every situation. The same boost levels in different weather conditions, such as a hot summer day and a cold winter month, can produce vastly different torque levels. 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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Manifold Absolute Pressure Sensor

To provide closed-loop boost control at absolute pressure levels above 2.5 bar, APR’s K04 Turbocharger System features an OEM Bosch 3 bar MAP sensor.

Altering the ECU to understand the engine is equipped with a 3 bar MAP sensor is a trivial task. The sensor and proper calibration settings come standard on many factory VAG vehicles, but even these vehicles only provide proper closed loop boost control up to 2.5 bar absolute.

APR’s electrical engineers went many steps beyond the norm and recoded the factory ECU to deliver closed-loop boost control up to 3-bar absolute. This ability, combined with proper torque management, results in safe, reliable, and predictable performance at higher power levels without the need for clumsy and archaic external boost controlling devices.

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Silicone Hose

A wire-reinforced, multi-ply silicone hose provide an unrestricted path for airflow exiting the turbocharger. The hose is engineered to properly connect the turbo’s outlet to the factory charge piping system.

APR’s Easy-Flow Silicone Hose design features stepped mounting surfaces for smooth transitions from one pipe to another. Traditional designs simply sit on top of each other, often resulting in a disruptive airflow path. By using the stepped design, hoses fit properly without airflow restrictions, resulting in the most ideal path for moving air through the turbocharger and into the engine.

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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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