Stage 2 is where the fun really starts to begin. Delivering epic performance through the mid-range you normally wouldn’t get off a stage 1 setup, stage 2 is a great addition if you seek that bit extra without changing turbo setups.
If you havent already done so, this guide will be a follow on from our Stage 1 guide which can be found here: 1.8T Stage 1 K03s. So your going to need a healthy running engine, good 99RON fuel, strong diverter valve as well as good oil and spark plugs.
Expected power you can aim to achieve from the stage 2 K03s is typically around the 230-250bhp mark with 280-300lbft torque.
The stage 2 mods are going to add a 3″ downpipe decat with a 2.5″ minimum free flowing cat back to the list of modifications, Large oversize silicone Turbo Intake Pipe (TIP) and Free flowing Front Mount Intercooler. There are other smaller modifications you can do for free/little cost such as the Secondary Air Intake (SAI) removal, Charcoal Canister Removal and N249 delete. Its also worth adding a catch can into the system and plumb it back into the intake. These cheap/free modifications are very easy to do and will make your engine feel a lot more crisper, run better and will give you slightly better results. It also removes a large amount of the pipework that is prone to leaks on the 1.8T engine such as the PCV pipe under the centre of the inlet to the one-way valve and old vacuum lines which may have cracks/splits. Renewing these with fresh 3-4mm vacuum tubing is highly recommended.
Stage 2 is still going to be limited by the K03s turbo, so the best thing we can do is to ensure that the airflow flows efficiently both into and out of the car from the beginning to the end. The whole setup has to work as a package and is key to great stage 2 performance.
A decat downpipe that’s a minimum of 2.75″ in diameter is also needed to help get rid of the excess exhaust gases out the system. 3″ is a lot more common and easier to get hold of, especially the ones off eBay, and again, these work a lot better. As we are removing the catalytic converter, which in itself is a restriction in the exhaust system, it is necessary to get a remap when fitting these as a lot of factors such as turbo spool, fuelling and error code lights will occur as a result. Any good mapper will be able to properly code/map these out leaving the rest of the fault code table intact, this will happen during a custom remapping session at your chosen tuner.
It is worth noting that we have seen more and more people fitting lambda spacers to the primary fuelling lambda. (This is the first one in the exhaust system from the turbo) This is NOT recommended and will cause problems with all your fuelling due to the sensor not being in direct flow of the exhaust gases.
Having a free flowing exhaust system will ensure that the gases can get straight out the tail pipe without creating too much back pressure in the system which will build up and choke the turbo.
Front Mount Intercooler/FMIC
A good free flowing Front Mount Intercooler or FMIC for short is crucial to ensuring the charge air pressure is adequately cooled down before it enters the engine. Colder air is better air and more dense. Another and the most important factor when choosing a FMIC is to ensure that the flow of the core and pipework is as good as it can be. A poor intercooler core can not only fail to cool down air at all, like we have seen with the Tube and Fin versions off eBay, but can also lead to a huge pressure drop across the core. One of the best coolers you can get is called the ‘Wellycooler’ – a name given in honour of the guy who first fitted the core to his 1.8T and found the results to be great. So cheers for that one Welly!
The wellycooler dimensions are a Toyosports Type B Bar and Plate core with 600x300x76mm in size. This is the most commonly used core for the setups, and will provide adequate cooling all the way up to and beyond 500bhp. Ideal if you plan a future upgrade to some point. There is also a smaller core made by Toyosports, again Bar and Plate, which is 550x250x63mm in size.
The pipework is a massive factor aswell. Having small 2″ pipes that are full of nasty tight bends isn’t going to help the air flow in the slightest and will cause a restriction. The more nearer to straight you can get your pipes will result in faster air flow. Of course, running straight pipes isn’t possible, but tight radius bends will slow air down in its path between the turbo and the engine. We recommend 2.5″ pipework when installing your setup. You may choose to have silicone couplers or choose to get your pipes welded together to reduce the amount of joins in the system which could result in pipes blowing off.
A popular setup about 5 years back was a uprated alloy Side Mount Intercooler which was a direct replacement for the stock item. However, these were found to be extremely poor by tuners testing them on the dyno and monitoring inlet air temperatures from on-board sensors. They were seeing air temperatures of around 70-80c which is astronomical compared to a good FMIC setup which can have peak temperatures of 25-30c on the hottest of UK days.
Whilst there are no ‘proper’ ways to fit a ‘Wellycooler’ setup, a good google search will reveal plenty of decent build threads of people who have fitted them. Research wisely and make notes of how people have routed their setup and choose the best flowing versions. A little bit of creativity is required here, but making that awesome flowing kit whilst ensuring the air is as cold as possible is more than possible.
Check out our Front Mount Intercooler page for more information on FMICs and some pics of setups on peoples cars
Turbo Intake Pipe (TIP)
One of the best modifications you can do to open up the airflow into the turbo is to change the turbo intake pipe to a over-size version which vastly improves the volume of air that can flow into the turbo. These range in price from about £60-£135 for the best TIP’s on the market.
As you can see from the above photo of 3 TIPs, there is a range of size difference between the three. The lower one in the picture is a cheap version off eBay and will offer you no better flow than the stock item. We have seen differences in 12bhp when comparing the smaller TIPs to that of a larger one. The top one, a Forge Motorsport version is a good flowing TIP, however there are lots better options out there which is shown in the photo below.
This photo shows the SFS ‘normal’ tip in black (which is similar to the Forge Motorsport one) compared with the Supersize TIP in blue. As you can tell in the picture the longer length of the TIP which goes down to the turbo inlet is vastly larger in diameter. Again, this increases the flow potential to the turbo. The supersize TIPs have been tested to over 300bhp and will work the the K03 hybrid turbos should that be a option you choose to go down later on.
As our 1.8T fuel pumps are getting increasingly tired with age, the most important factor of modifying any engine is the ensure that there is sufficient fuel being supplied to the injector rail. This prevents the fuel system from being lean and resulting in a weak air/fuel ratio mixture which will ultimately lead to melted pistons or other parts melting.
For further information, please have a look at our fuel pump advice page for further advice. 1.8T Fuel Pump Advice
What about the AGU?
The AGU engine is a older and completely different management system to the newer fly-by-wire setups, so a lot of the sensors are different. There are two main ones that we need to address with pushing stage 2 K03s on a AGU, especially if you want a touch more power. There are the injectors, which max out at 225-235bhp and the MAF sensor tube.
As the AGU does a lot of the ECU calculations via the MAF sensor and Load tables, upgrading both the MAF sensor tube and injectors is recommended to be done at the same time. Plus it will make your tuners live a bit easier when he comes to live tune the car on the rolling road (there are no flash and go maps at stage 2 level for the K03s that we know of!)
The Injectors you will need are the Calibra Turbo Yellows or Saab Reds if you want to have a bit more headroom. The MAF tube you need is a OBD2 VR6 housing which measures 2.75″ in diameter. The newer 3″ versions off the LCR and S3 dont fit as the sensor fitment is different. You will need to swap your ORIGINAL 1.8T sensor over into the larger 2.75″ tube and discard the VR6 sensor which we don’t need. So to recap….1.8T sensor in the VR6 2.75″ MAF tube.
If you fancy pushing for that little bit extra, you can always change your turbo actuator and fit a Water Methanol Injection kit. See below for a outline of each.
Over time, the stock actuator can become weak and as we push for more and more power from the K03s, then the actuator cant physically hold back the exhaust gases. So what happens is that instead of the actuator holding the wastegate firmly closed, enabling boost to be held over the midrange-high RPMs is the wastegate gets pushed open allowing exhaust gases to bypass the turbine. A stronger actuator will prevent this and give your tuner more control over the turbo and the boost it can produce without requesting maximum N75 valve duty to try and get the turbo to make more boost.
As with any actutor, there is a wide range of spring pressures you can buy. These range from about 7psi which is around stock all the way to 15psi spring settings. The spring pressures are NOT a indication of the boost pressures they will give you. This is the wastegate cracking pressure as to when the actuator starts to move to allow the wastegate to open. With a small turbo like the K03s, there is absolutely no need/requirement to run such a strong spring pressure such as 15psi as this will simply stop the wastegate from opening up at low boost pressures and give poor boost control via the ECU. A 10-12psi actuator spring is the maximum you will need for a K03s as the K03s simply cant offer any more than 12-13psi of boost pressure at higher RPMs as it runs out of puff and becomes a heat pump.
A great video tutorial on setting up a actuator on a K03/K03s turbo can be found here.
The stock K03 manifold is very well designed, even from the factory. Much better than its larger K04 brother which is very poor flowing. A little cheap and simple modification to do is to port the stock manifold to open it out a little and allow the gases to flow a lot more freely. There are many companies that offer this service such as Badger5 LTD or JNL Racing who are very reasonably priced. A well ported K03 manifold will not only help with the flow of gases, but help with keeping the whole turbo setup cooler due to there not being as much restriction. Cooler the better! A ported manifold is required if going K03 Hybrid route later on.
Water Methanol Injection
Water methanol injection is becoming one of the most increasingly popular additions to have to any turbo car. Methanol has a RON rating of around 115RON. Combined with water and when this mixture is injected into the charge pipework after the intercooler and before the Inlet Air Temperature Sensor, then not only do you get a kick of high RON fuel entering the engine, the water in the mixture draws he heat out of the air cooling the charge air pressure down by massive amounts.
We wont touch on Methanol Injection much on this page, but we have a dedicated page under Engine Advice with details the whole setup in much more detail and give the advantages and disadvantages of running Water Methanol Injection. See the link below:
The next stages for more power are to look at hybrid turbos or a turbo conversion such as the K04 turbo or fit the larger K04-064 turbo as found on the Mk5 TFSI engines. We have separate pages for them and their benefits so take a look at those if your fancy that bit more power.