Inside Look: KO4 Turbo Upgrade for TSI Engine Audi / Volkswagen’s

If you spend any time on the Audi/VW platform you will at some point come across turbo upgrades. The infamous Ko4 turbo upgrade path being one for the MK5/6 GTI’s and select Audi’s. So what are these popular turbo upgrades? What cars are they for? And more importantly should you take a look at this before fleshing out your next project car build?

For the sake of this article we will discuss the TSI engines. There are other kits which work for the FSI model years (MK5 GTI’s with BPY engine code). But for fitment and performance output we will use the TSI applications

Above is a fitment chart for a typical Ko4 turbo upgrade kit on for the TSI engine cars.

At the core of the Ko4 turbocharger kit from pretty much every brand is the Borg Warner Ko4 turbocharger. This turbo is found in select Audi S3 models in Europe at the time. So larger flow backed by OEM quality is what makes this kit the perfect aftermarket option for the tuner who wants a reality daily driver with some extra power behind it.

Now some of the first questions we usually get around turbo upgrades comes price and install. P

The actual turbocharger kits can vary by brand as some manufacturers such as Unitronic offer their kits combined with tuning software but if we look at the core Ko4 turbo kits from brands such as CTS Turbo you are at around $1950 or so. Labor rates can vary but if you are a do it yourself like ourselves this is not that hard of a job to swap out. Full installation guides can be found on

Now one thing to consider with price is the ko4 turbo kits will require you to buy some supporting mods. Some you may already have and some you will not.

High Flow Downpipe

The Ko4 upgrade path is going to require you to not have that restrictive stock downpipe and rather a high flowing downpipe. Many options are on the market and at Modded Euros we have a whole slew of them. Now if you are already running a modified stage 2 car you most likely already have this part. The downpipe required is no different than any other downpipe you would run on your car. Its not specific fitment to the Ko4.

Tuning Software

One other key factory when adding a larger turbo to your car is making sure your car’s software is tuned for this new turbocharger. For cars already tuned by popular tuners like Unitronic or Integrated Engineering it is a simple tune upgrade which can be done on For those of you running stock cars looking to jump right to stage 2+ and run the Ko4 you will need to pick which tuning software you want to run as well as get that brand’s at home tuning cable.

Unitronic’s at Home Tuning Cable

At Modded Euros we offer tuning options from both Unitronic and Integrated Engineering which you can flash right at home.

Quick video on how easy it can be done is seen here in our Unitronic UniConnect+ cable overview video:

Now generally if not the first but the next question becomes “How much power?!”

Power can vary slightly by model car but to give you an idea a MK6 GTI can expect to pick up a whopping +140hp and +123TQ over the stock numbers. That’s enough to churp your wheels while rolling and put a smile ear to ear.

Here at Modded Euros we are always striving to pump out content and with our Project Car series we have filmed what it takes to go from Stock to Stage 2+ on a MK6 GTI. Below is episode 5 in our MK6 video series highlighting the Ko4 turbo upgrade we went with. Check it out and let us know in the comments what you think:

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