Stage 1 K03s

Typically, we don’t really use the term ‘Stage’ when tuning a car, but for use with a K03/K04 turbo, its a good indicator for the level of power you want and what modifications your going to need.  We outline the best 1.8T Stage 1 K03/s advice below.

Stage 1, is generally remapping a totally stock engine, or having a few basic modifications such as uprated air filter or cat back exhaust system.

The early K03 engines, which don’t have the K03s turbo, such as the AGU engine code, will typically remap to around 190bhp and 220lbft at stage 1.  Unfortunately, the K03 turbo is the restricting factor, so should you want more power, then its advised to upgrade to a K03s turbo, which is a direct bolt on replacement (minus a slightly different stock intake pipe).
A list of engine codes which have the K03 turbo are: AEB ,AGU ,AYP, ARZ, APP, AJH, AJL, APU, AQX ,AWT, AWU, BFB

The later engines, found in cars after ~2001 all come with a K03s as standard.  With just a stage 1 remap, this setup will typically remap to around 210bhp and 245lbft, which is huge delta gains over stock performance even from just a remap.  Which will give you a huge grin when you take the car out on a test drive after its just been mapped.
A list of engine codes which have the K03s turbo are:  AUM, AUQ, BBU, BJX, BVP , AWV.

As with any level of remap, its vital that the engine is performing as it should be otherwise any issues which might not be present at stock level, will be highlighted once tuned such as tired N75 valve, MAF sensor, poorly connecting boost pipework, quality of fuel.

Health Checks

During your remap session, your tuner should be doing a full health check of all engine pipework, a smoke test to identify any split or leaks in the charge/vacuum pipework, and data logging on stock hardware to ensure everything is running correctly prior to adding more power from a remap.  A healthy running engine is key to making power from a remap.  The remap software isn’t going to fix any hardware issues you may have.


We advise running a good quality fuel, such as Shell V-Power or Tesco Momentum 99.  The standard supermarket fuel at 95RON is no where near good enough to run in a remapped engine and could see power levels drop in a range of 10-25%!  This is because the fuel is more prone to knock, so the ECU picks up on this and reduces ignition timing.  A great insight into this is the Fifth Gear Fuel Test which was shown on TV a few years back done with R-Tech Performance who noted gains of 13bhp and 13lbft just from different brands of fuel.  This was on a completely stock engine, so on a tuned engine, this will be even greater!  Its a no-brainer for unlocking extra power.  A fresh fuel filter is also recommended as over time, they can get clogged up, which reduces fuel flow to the injector rail.

Diverter/Dump Valve

Another thing to check or replace prior to your stage 1 remap is the dump/diverter  valve.  This valve recirculates air back through the turbo intake pipe when you let off the throttle.  A airtight valve is crucial for making power as if its leaking boost pressure then this can cause power loss and turbo lag.  A great option for stage 1, and even stage 2 and above, is a Forge 007p valve or even a genuine stock replacement from the main dealers.  Part number: 06A 145 710 N at a price of around £30.  The 710N is a revised unit over stock so for the sake of £30 its definitely recommended to change your old and tired valve out for a newer replacement.  If you know the history of the valve you have, you need not change it if its known to be airtight.
Keep away from anything that dumps the pressure to atmosphere.  Commonly known as a Blow Off Valve (BOV).  These release the air into the atmosphere and are generally favoured because they make a ‘Whoosh’ noise.   However, since the air released has been accounted for via the MAF sensor, the ECU has adjusted fuelling for the amount of air that’s past the air flow sensor, so you will get fuel trims increasing due to a air leak in the system from the BOV.  Also, blowing off the air to atmosphere increases turbo lag and makes the car much ‘flatter’ when tipping in the throttle between gear changes or accelerating.

Spark Plugs

Spark plugs are another key factor.  A fresh set certainly won’t go amiss before a remap.  Two of the best plugs you can get for the 1.8T are the NGK BKR6E (copper)  or the NGK BKR6EIX (platinum).  If you want to go a step cooler then the numbers are NGK BKR7E (copper) and NGK BKR7EIX (platinum).  Stage 1 will be fine with the 6 or 7 heat range however if stage 2 then we recommend the 7 heat range which is a step cooler.


A good quality oil such as Quantum Platinum 5W-40 from the main dealers or TPS from as little as £20-25 is recommended.  As we mentioned above, a healthy running engine is also a happy engine, which will make power.  A simple oil and filter change along with the above can make the world of difference.  Also, don’t forget to CHECK YOUR OIL!!!  It’s no good turning up for your remap with oil that’s 20,000miles old and sat a tiny bit above minimum.   Remember, your engine will be working a lot harder with a lot more heat than before, so ensure its well looked after.

Want a little more?

If your after a little bit more from your stage 1 remap, or looking at making the transition into stage 2 for more power, then the best way forward is to improve the flow of air through the turbo, across the engine and out of the exhaust.   The greater the flow of air, the more power you make.  Don’t forget that the flow of air has to be efficient and non-restrictive with the modifications otherwise, you may find yourself hitting a brick wall during tuning and your search for more power.  Don’t worry though, we have a list of all the best flowing modifications to get so you get the best performance!


One of the best modifications to do at stage 1, either before or after a remap is the turbo intake pipe.  There are a wide range of silicone pipes on the market and the quality varies vastly.  Keep away from the £50 specials on eBay which are more restrictive than stock and don’t offer any more flow.

Three of the best on the market are the Forge, SFS supersize and the R-Tech Performance versions.  These are around the £130 mark and are a great addition to stage 1 and for the transition into stage 2.   With a Turbo Intake Pipe, the greater the size, the better airflow it can deliver.  In the last 5 years or so recent developments by the top U.K 1.8T tuners found that increasing the size of diameter of pipe onto the turbo resulted in great gains across points of the rev range and gave much better top end performance.  This is how the term ‘supersize’ came about and the size is typically around 70mm or greater all the way to the turbo.  The Forge TIP isn’t supersize, however, if you just want a great quality intake pipe for a stage 1 map, this is a great option.

As with any modifications, doing too much after a stage 1 remap, can cause issues with how the car runs, such as 3″ decat downpipes which change how the turbo spools etc.

If you have the tuning bug and want to get more power, then take a look at your 1.8T K03s Stage 2 Guide Here.

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