From the K03-equipped 1.8T to the IS38 on the Golf R, through the RS3 2.5T and RS6 twin-turbo 4.0T -- Boost Lab rebuilds the full VW and Audi turbo ecosystem. Oil coking is the defining failure of this platform. We have seen it more times than we can count.
Three distinct turbocharger generations span the VW and Audi lineup. Each has its own bearing architecture, failure patterns, and rebuild considerations. Knowing which generation your vehicle carries is the starting point for any rebuild conversation.
The K03 and K03S were the workhorses of the 1.8T 20V era. The K03 uses an 11-blade compressor wheel; the K03S upgrades to 8 blades and pairs with the drive-by-wire AUM and similar engine codes. The two share the same footprint and are effectively interchangeable. Actuator spring rate (65N vs 85N) varies by power output -- the 180hp applications use a stiffer actuator and should be rebuilt with the correct spec unit.
The K04 comes in two configurations that are not interchangeable. The K04-001 (transverse) is a direct bolt-on upgrade for K03 and K03S applications on transverse 1.8T engines. The K04-023 is fitted to Quattro AWD platforms (S3 210hp, TT 225 Quattro) with a different exhaust manifold and downpipe geometry. The 2.0T EA888 Gen 1/2 also uses a K03 variant -- commonly misidentified as a K04 by owners.
The MQB platform introduced the IHI IS-series turbos. The IS12 covers 1.8T MQB applications; the IS20 is standard on 2.0T lower-output MQB; the IS38 is factory-fitted to the Golf R, Arteon, S3 8V, and TTS. The IS38 is also the most popular single upgrade in the VAG community -- a direct bolt-on for any IS20 application with a tune. Thrust bearing wear is the primary rebuild item on tuned IS20 and IS38 units operating above factory boost targets.
The RS3 and TT RS use Audi's 2.5T inline-5 TFSI engine with a single twin-scroll IHI turbocharger -- one of the more characterful turbo setups in the VAG lineup. The RS6, RS7, S6, S7, and S8 4.0T use twin BorgWarner turbos positioned in the valley between cylinder banks (hot-vee configuration), which creates unique oil drain challenges and elevated thermal load on the bearing housings. These are high-value, high-complexity rebuilds.
The TDI lineup spans a wide range of turbo configurations depending on displacement and generation. The 1.9 TDI uses a variable-geometry turbo with a common actuator failure mode. The 2.0 TDI PD and CR generations use BorgWarner units; the 3.0 TDI uses twin sequential turbos with a low-pressure and high-pressure stage. All TDI turbos are oil and water cooled and require full cooling circuit inspection at rebuild.
The Audi 2.7T biturbo (S4 B5/B6, A6 2.7T, Allroad) uses a pair of K03 turbos in a twin configuration. Both turbos should be rebuilt as a set -- replacing only one leads to asymmetric boost delivery and accelerated wear on the rebuilt unit as it compensates for the degraded twin. The 2.7T is known for oil sludge accumulation in the valley between the cylinder banks, which directly impacts turbo oil feed quality.
Search by model, turbo designation, or engine code. Use this table to identify your turbo before submitting a rebuild request.
| Turbo | Application | Engine / Code | Mfr | Notes |
|---|---|---|---|---|
| K03 | Audi A4 B5 1.8T 150hp | AEB / ANB | KKK/BW | 11-blade compressor, 65N actuator |
| K03S | Audi A3 8L / A4 B6 1.8T 150hp | AUM / AWW | KKK/BW | 8-blade, drive-by-wire |
| K03S | Audi TT 8N 1.8T 180hp | AWP / AMK | KKK/BW | 85N actuator, higher boost |
| K03S | Audi S3 8L 210hp | AMK / BAM | KKK/BW | FWD only; AWD gets K04-023 |
| K04-001 | VW Golf / Jetta / A3 1.8T upgrade | Multiple | KKK/BW | Direct K03 replacement, bolt-on |
| K04-023 | Audi S3 8L Quattro / TT 225 Quattro | AMK / BAM / APX | KKK/BW | AWD platform only; different downpipe |
| K03 (BWA) | VW Golf Mk5 GTI / Jetta GLI 2.0T | BPY / BWA / AXX | BorgWarner | EA113; K04 upgrade needs injectors |
| K03 (EA888) | VW Golf Mk6 GTI / Jetta GLI | CBFA / CCTA | BorgWarner | EA888 Gen 1; chain-driven cam |
| K03 (EA888) | Audi A4 B8 / A5 / Q5 2.0 TFSI | CDNB / CAEB | BorgWarner | Longitudinal; water-cooled bearing |
| K03 (EA888/2) | VW Passat B7 / CC 2.0T | CBFA / CCZA | BorgWarner | Gen 2; similar to Gen 1 turbo |
| IS12 | VW Golf Mk7 1.8T / Jetta 1.4T/1.8T | CPMA / CHPA | IHI | MQB 1.8T; baseline MQB turbo |
| IS12 | Audi A3 8V 1.8 TFSI | CJSA / CJSB | IHI | MQB platform |
| IS20 | VW Golf Mk7/7.5 GTI | CHHB / CHHA | IHI | Stock 220hp GTI; upgrade to IS38 w/ tune |
| IS20 | VW Jetta GLI A7 / Tiguan MQB | CHHB / CZPB | IHI | Same unit as GTI |
| IS20 | Audi A3 8V 2.0 TFSI / TT Mk3 2.0T | CJXB / CJXA | IHI | MQB longitudinal; IS38 bolt-on |
| IS38 | VW Golf R Mk7 / Mk7.5 | CJXC / DKZ | IHI | Factory 310hp; thrust bearing wear on tune |
| IS38 | VW Arteon 2.0T | DNUE | IHI | Same family as Golf R |
| IS38 | Audi S3 8V / TTS Mk3 | CJX / CJXB | IHI | Factory fitment; IS20 upgrade target |
| 2.5T IHI | Audi RS3 8P / 8V / TT RS Mk2 | CEPA / CZGC | IHI | 5-cyl twin-scroll; single unit |
| 2.5T IHI | Audi RS3 8Y (2022+) | DNWA | IHI | Updated 5-cyl; 400hp factory |
| K03 Twin | Audi S4 B5 / B6 2.7T | AGB / AZB / BES | KKK/BW | Rebuild as matched pair |
| K03 Twin | Audi A6 C5 2.7T / Allroad 2.7T | AGB / AZB | KKK/BW | Oil sludge inspection required |
| BW 4.0T Twin | Audi RS6 / RS7 C7 4.0T TFSI | CGTA / CTBA | BorgWarner | Hot-vee; both turbos rebuild together |
| BW 4.0T Twin | Audi S6 / S7 / S8 4.0T TFSI | CGTA / CTBA | BorgWarner | Same twin as RS6/RS7 |
| BW 4.0T Twin | Audi RS6 / RS7 C8 (2020+) | DGGB / DDYS | BorgWarner | Mild hybrid; updated turbo architecture |
| BW VNT | VW Jetta / Golf / Passat 1.9 TDI | ALH / BEW / BRM | TDI | Variable nozzle; actuator failure common |
| BW K03 TDI | VW Golf / Jetta 2.0 TDI PD | BKD / BMN | TDI | Pumpe Duse injection; different oil spec |
| BW 2.0 TDI | Audi A3 8P / Golf Mk6 2.0 TDI CR | CBAA / CBAB | TDI | Common rail; revised bearing housing |
| BW 2.0 TDI | Audi A4 B8 / Q5 2.0 TDI | CAHA / CAGA | TDI | Water-cooled bearing housing |
| BW Twin Seq. | Audi A6 C6/C7 / A7 / Q7 3.0 TDI | CLAA / CRCA | TDI | Low-pressure + high-pressure stages |
| BW Twin Seq. | Audi A8 3.0 TDI / Q7 3.0 TDI | CCWA / CRCD | TDI | Full cooling circuit inspection required |
A turbo out of the car is an opportunity. Both of the most popular VAG performance upgrades are direct bolt-on swaps requiring only a tune -- if your turbo is already coming out, the incremental cost of stepping up is low.
The K04-001 is a direct bolt-on replacement for the K03 and K03S on transverse 1.8T applications. It flows more and supports higher boost levels than the K03S. If your 1.8T K03 is out for rebuild, stepping to a K04-001 is the same installation effort with a meaningfully different power ceiling.
Important: On EA113 2.0T applications (BPY/BWA engine codes), K04 upgrade requires injector upgrades as the factory injectors cannot flow enough fuel at K04 boost levels. EA888 engines do not have this limitation.
The IS38 is a direct bolt-on replacement for the IS20 on all MQB 1.8T and 2.0T applications. Factory fitment on the Golf R and S3 means it is a production-proven unit at significantly higher output. The IS38 flows more on the top end while adding only a small amount of spool lag at lower RPM -- a trade most tuned GTI owners find worthwhile.
Tune required: Running an IS38 on IS20 software causes boost control issues. A proper tune is required before driving the vehicle with the IS38 installed.
Start a rebuild request online. Ship your turbo to Dade City, FL and we handle the rest.