VAG Turbo Families – VW/Audi/Seat/Skoda 1.8T 20V R4 transverse engines

VAG Turbo Families – VW/Audi/Seat/Skoda 1.8T 20V R4 transverse engines

There are three names you will find when looking for turbos on 1.8T 20V transverse engines. K03, K03S and K04. Each one being bigger than the one before.
K04 comes in two flavours: K04-001 and K04-023.

K04-001

K03, K03S and K04-001 are direct replacements of one another. The K04-023 comes with a completely different intake system, exhaust manifold and requires a different downpipe. This difference exists because it was only installed on 4WD drive platforms, where the transmission axle makes things different in the exhaust geometry.

Be careful, these turbos are not the same with the K03 and K04 installed on longitudinal engines, like the Audi A4 and VW Passat.

Transverse engines exist in the following very popular models amongst the VAG group:

• Audi A3 8L (K03 on mechanical throttle, K03S on drive-by-wire systems)
  

  K03

• Audi S3 8L (K04-023 on all versions)
• Audi TT 8N (Only drive-by-wire system exist. K03S on 150hp and 180hp versions, K04-023 on 210hp/225hp versions)
• VW Golf Mk IV (K03 on mechanical throttle, K03S on drive-by-wire systems)
• VW Bora (K03 on mechanical throttle, K03S on drive-by-wire systems)
• Seat Leon MK I (K03 on mechanical throttle, K03S on drive-by-wire systems, K04-023 on Cupra)
• Seat Ibiza (K03 on mechanical throttle, K03S on drive-by-wire systems)
• Skoda Octavia (K03 on mechanical throttle, K03S on drive-by-wire systems)

Now a few rules so that you can identify them more easily

The first generation of transverse 1.8T 20V engines with a mechanical throttle had K03 turbos. Up to model year 2000, everything used K03.
K03 turbo on the following engine codes:

• AGU (on VW Golf 4 GTI, Audi A3, Skoda Octavia)
• AJH (VW Sharan, Seat Alhambra)

With the appearance of modern electronics and OBD2-compliant systems, throttle control became fully electronic. Drive-by-wire systems marked the appearance of K03S, which is a significantly larger turbo than the K03.

K03S turbos exist on engine codes:

K03s

• AUM (Golf, Octavia, A3, Leon – 150hp)
• AUQ (Golf, Octavia A3, RS, Leon – 180hp)
• BBU
• BJX
• BFB
• BVP
• AWV
• AWP (VW Jetta)

Upgraded versions of the 1.8T 20V engines with 210hp or 225hp appeared with OBD2 compliant electronics and Drive-by-wire systems too. They always use a K04-023 turbo because they are all 4WD:

K04-023

• AMK (210hp)
• AMU
• BAM (Audi TT and S3 – 225hp)
• APX (Audi TT – 210hp)
• APY (Audi S3 – 210hp)
• BFV