1.8 Litre Turbo Engines in Volkswagons and Audis
The 1.8T engine was basically Volkswagon's and Audi's bread and butter engine when it was originally designed. For Audi, a premium brand, it was to be base engine and for VW the mid range or premium choice. Audi has long had a history of turbo charging and with many advances in the components and design it all made sense. That being said, if you buy an Audi you almost always get all wheel drive and in a car thats full of electronics and crash protection 150 horsepower kinda sucks. The engine is very efficient and has a broad torque band but the top end is really lacking. There was an upgrade to A4s in 2001 and it made a difference but in
my opinion, not much. The nice thing about turbocharging is the aftermarket will come out with a lot of products and you can now make serious power without having to loose your shirt in the process. 
The basic Ko3 Turbo that comes in the standard A4 is small and efficient efficient with very little lag. The key to the set up is the boost (turbo pressure) is regulated by the engine computer. As is the ignition and fuel basically like all modern vehicles. Just basic software upgrades that increase boost and adjust the fuel and ignition timing accordingly increase performance dramatically. A lot of people ask me why Audi does not provide the car with more horsepower if all it needs is a software reprogramming. The answer is simple. 1. Reliability of the engine now does down. Stress on the engine internals as well as transmissions, driveshafts, final drive, axles and its splines now becomes an issue. The cost to upgrade these parts would influence the price of the vehicle too much.2. Increased maintenance. Since there is all this extra stress of all these driveline components, the fluids now need to be changed more often. Yes, even the synthetic oil needs to be changed more often. Once the car is modified the service recommendations are now more frequent.
3. Economy. All vehicles must meet emissions emissions and fuel economy standards and this software would increase consumption and decrease economy too much.
The software is considered the most basic of upgrades. It is easy, does not require any major tools or hard labour. But when you want more is when it all starts to add up. Because of the increased boost you will need a diverter valve. The OEM one is rubber and eventually fails anyways when the rubber falls apart causing a vacuum leak. Piston types that are rebuildable are for sure the way to go. I have had excellent experience with Forge units.
Next is the factory exhaust. The catalytic converter on 1.8Ts are very restrictive and the mufflers are very large and heavy. Just replacing the large mufflers makes a noticeable difference. If the Converter and system is replaced the turbo lag will be reduced even more along with increased power through the rev range. 1.8Ts run very hot and the exhaust on a tuned 1.8T is extremely hot. I have had excellent experience with thermal coating and ceramic products that keep the heat inside the exhaust system. DEI makes a silicone ceramic product that looks good and is easy to apply yourself. Intakes that eliminate the large and restrictive air box and turbo inlet pipe are also important to keep the system consistent. Most of the power found with installing an aftermarket intake is at the top end.
With just those upgrades you can expect around 230- 245 crank horsepower on just the stock engine.
That is basically a stage 1 set up and is limited to the factory turbo. The Ko4 turbo is then the obvious choice for a stage 2 upgrade. The Ko4 is commonly found on S4, RS4 and TT 225 horsepower models. It has the same exhaust housing and turbine as the Ko3 but a larger intake compressor. It is identical in fitment to the Ko3 making installation easy and painless (as a turbo replacement can be). I have done the install and its not that bad. A front mount intercooler that replaces the small side mount intercooler is important. The side mount is not bad even though it is small, it is just placed in a poor spot for maximum air flow. Stock A4 bumpers also have little air flow through them. Consider adding an intercooler fan as well. A Methanol water injection kit works EXTREMELY well with the 1.8T mainly because of the heat the engine naturally makes from a highly tuned smaller turbo engine. You will also need colder range spark plugs for this application. With a maximum tuned Ko4 setup with meth inject and ignition timing to match you potentially see 280 to almost 295 crank horsepower on a stock engine. This is a very common setup and probably the best when you compare performance to dollars spent.
Upgrading to a ball bearing turbo like the units produced by Garrett are also common. Many tuners claim 350 horsepower on the stock engine with larger GT30 or GT35 units. One must consider reliability when switching to these setup because these are basically race car products.
Many consider the AEB engine code the best production 1.8T. It was designed before stricter emissions came into play so it was larger intake ports and track. It is widely renowned for reliability and it is also exempt from electronic throttle problems as it was the generation of 1.8Ts that had a cable throttle. Many drivers say that consistently run 26 or more PSI through these engines with out a problem.
3. Economy. All vehicles must meet emissions emissions and fuel economy standards and this software would increase consumption and decrease economy too much.
The software is considered the most basic of upgrades. It is easy, does not require any major tools or hard labour. But when you want more is when it all starts to add up. Because of the increased boost you will need a diverter valve. The OEM one is rubber and eventually fails anyways when the rubber falls apart causing a vacuum leak. Piston types that are rebuildable are for sure the way to go. I have had excellent experience with Forge units.
Next is the factory exhaust. The catalytic converter on 1.8Ts are very restrictive and the mufflers are very large and heavy. Just replacing the large mufflers makes a noticeable difference. If the Converter and system is replaced the turbo lag will be reduced even more along with increased power through the rev range. 1.8Ts run very hot and the exhaust on a tuned 1.8T is extremely hot. I have had excellent experience with thermal coating and ceramic products that keep the heat inside the exhaust system. DEI makes a silicone ceramic product that looks good and is easy to apply yourself. Intakes that eliminate the large and restrictive air box and turbo inlet pipe are also important to keep the system consistent. Most of the power found with installing an aftermarket intake is at the top end.
With just those upgrades you can expect around 230- 245 crank horsepower on just the stock engine.
That is basically a stage 1 set up and is limited to the factory turbo. The Ko4 turbo is then the obvious choice for a stage 2 upgrade. The Ko4 is commonly found on S4, RS4 and TT 225 horsepower models. It has the same exhaust housing and turbine as the Ko3 but a larger intake compressor. It is identical in fitment to the Ko3 making installation easy and painless (as a turbo replacement can be). I have done the install and its not that bad. A front mount intercooler that replaces the small side mount intercooler is important. The side mount is not bad even though it is small, it is just placed in a poor spot for maximum air flow. Stock A4 bumpers also have little air flow through them. Consider adding an intercooler fan as well. A Methanol water injection kit works EXTREMELY well with the 1.8T mainly because of the heat the engine naturally makes from a highly tuned smaller turbo engine. You will also need colder range spark plugs for this application. With a maximum tuned Ko4 setup with meth inject and ignition timing to match you potentially see 280 to almost 295 crank horsepower on a stock engine. This is a very common setup and probably the best when you compare performance to dollars spent.
Upgrading to a ball bearing turbo like the units produced by Garrett are also common. Many tuners claim 350 horsepower on the stock engine with larger GT30 or GT35 units. One must consider reliability when switching to these setup because these are basically race car products.
Many consider the AEB engine code the best production 1.8T. It was designed before stricter emissions came into play so it was larger intake ports and track. It is widely renowned for reliability and it is also exempt from electronic throttle problems as it was the generation of 1.8Ts that had a cable throttle. Many drivers say that consistently run 26 or more PSI through these engines with out a problem.
With A4s available on the market for $4000 to $10000cdn for decent maintained examples it is becoming a very appealing car to tune. Tuning a naturally aspirated engine from 150 horsepower to 250 on a BMW or Mercedes could cost tens of thousands of dollars and still not make the torque that a 1.8T does. Of course the car is not bulletproof as it does have its service and maintenance issues but if you are looking to go fast on budget, 1.8T may be your best bet.
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