The TT, in both 180hp and 225hp flavors, comes stock with a dinky turbocharger that has propelled it into being the butt of jokes stating that "TT" stands for "Tiny Turbo." Indeed, a lot of TT owners wonder about the feasibility and benefit of OEM turbo swaps, especially 180 owners out there looking for a little extra oomph. So let's get a rundown of the turbos used in the TT:
The TT uses a single turbo manufactured by KKK, Kühnle, Kopp & Kausch, which is owned by the larger company Borg Warner. 180hp models use a variant of the K03 turbo, whereas 225hp models use a variant of the K04. A lot of people get confused with the K03/K04 because they don't realize that there are many variations of the two. A good breakdown of K04's can be found here:
A quick breakdown...
The K03 comes standard in some early 1.8T engines. Check out the Vortex 1.8T FAQ to find out which yours has. Variants of the K03 are used on other cars as well, such as the turbo Mini Coopers.
The K03 sport (K03s) comes standard in later model 1.8T engines. It can make slightly more power and is a direct bolt on for any K03 based car.
The K04-001 uses some K04 internals and a K03s housing. It is a direct bolt on for any K03/K03s car but makes a fairly small power difference above a K03s.
The K04-020 is the stock turbo for the 225hp TT. It requires a new manifold, downpipe, oil/coolant lines and turbo inlet pipe to use, however. It makes decent power over the K03s, but most people say it's not worth the work/money for the conversion and they would have rather just gone with a big turbo.
To get the most out of a K04, one will need a set of bigger injectors and software for them as well.
Power wise, the K03s typically sees 220whp with lots of bolt ons. The K04-001 might make slightly more than that. A maxxed out K04-020 can see around 250whp.
A thing to watch out for when buying these turbos is whether they are made for longitudinal engine cars (A4, Passat) or transverse engine cars (TT, Golf, Jetta).
Fortunately, they're not hard to identify. This is a pair of longitudinal turbos...the outlet of the compressor housing is stubby:
Now this is a transverse K03 (bottom) and K03s (top). Note the elongated outlet on the compressor housing compared to the longitudinal turbos above. Easy way to tell the difference between K03 and K03s is look for the muffler on the compressor outlet, most K03s turbos have one, most K03 turbos don't. More reliably, you can count the number of fins...K03 has 12, K03s has 8:
This is a transverse K04 kit. Again, note the elongated outlet on the compressor. Also note the inlet pipe and exhaust manifold required to install it.
Here's an email from Borg Warner. Notice how they don't call it a K03s...however they offer good info on the specific model designations of their turbos:
thank you for your interest in our products.
First of all, we don't produce any turbo that we call K03S. But I hope I can
answer your questions with the following explanations.
All the following turbos have the same installation dimensions and
thermodynamical performance. The differences are only in the actuator that
opens the turbine bypass valve:
K03-011 (5303 988 0011) 150 hp, 65 N actuator
K03-026 180 hp, 85 N actuator
K03-035 180 hp, 85 N actuator
K03-044 150 hp, 65 N actuator
K03-045 156 hp (Ibiza Cupra), 85 N actuator with 2 ports
K03-049 150 hp (Sharan/Alhambra), 65 N actuator
The 180 hp versions have an actuator with a higher opening force due to the
higher exhaust gas pressure (which is a consequence of the higher boost
pressure). Otherwise the valve would be pushed open by the exhaust gas
The following turbos are a further development (since 2000) and have an
improved and slightly larger compressor while using the same turbine (still
with the same installation dimensions):
K03-052 180 hp, 85 N actuator
K03-053 150 hp, 85 N actuator
K03-058 150 hp/180 hp, 85 N actuator
Consequentially, putting a 180 hp turbo on a 150 hp engine will not bring
about any change in performance, but putting on a K03-052/053/058 instead of
the older versions will bring a slight improvement in engine efficiency.
Additionally, with re-mapping the ECU you can achieve about 215 hp without
danger of overspeeding the turbo. With the older turbos, 195 hp is the
With the K04 that's also commonly used (5304 950 0001) the power output
should not be more than 220 hp. That means, changing a K03-052/053/058
against a K04 does not make a lot of sense.
I hope that these details answer your questions. If you need more info, one
of our service distributors will be glad to help you. Their addresses are on
our website www.turbodriven.com.
Mit freundlichen Grüßen/Best regards,
BorgWarner Turbo Systems GmbH