The fourth generation Golf GTI, known as the MKIV, is one of the best GTIs VW has produced over the years. After losing a bit of the plot with the third-generation GTI, the MKIV returned to the GTI’s roots: being a fun-to-drive three- or five-door car. Part of its appeal is the 1.8-liter turbo engine that was available in 1997 through 2006 models. There are two variants of this engine, the 138 hp and the more powerful 178 hp. Both engines are well suited to tinkering.
As with many turbo cars, this engine is perfect for modifications. It’s easy to get over 200 horsepower and there have been MKIVs prepared with over 500 hp. GTI owners can take several steps to get more horsepower out of their particular model.
One of the most common and effective ways to get more power from a 1.8T engine is by reprogramming the ECU (Engine Control Unit). This changes the ignition and fuel injection maps to give them a more aggressive curve, as well as raising the rev limiter and top speed limiter. The ’99 through 2001 models will end up with 195 to 200 hp, while the 2002 and later models will get 220 hp. Companies like Neuspeed offer this service (which requires them to have your car’s ECU) for around $400 (September 2009 prices).
You can also replace the 1.8T’s restrictive standard air intake with a cold air intake like the one Motorsport Evolution offers for $189. This adds 8 to 12 hp. The $299 V-Flow intake adds 10 to 15 hp. Most companies that make parts for the GTI offer air intakes.
Turbo cars benefit greatly from a free-flowing, larger-bore exhaust, and the GTI is no exception. A sport exhaust, such as the one produced by the APR firm, generally guarantees another 10 to 15 hp.
Heat is the enemy of horsepower, so a larger heat exchanger is also a good idea. By providing more cool air for the turbo, the engine gains more horsepower. Adding a heat exchanger is also an important step if you decide to fit a larger turbocharger.
By far the biggest increase in horsepower on a 1.8T engine comes when the relatively small factory turbocharger is replaced with a larger one. GReddy makes a turbo kit that uses a TD04H-19T with a larger turbine and compressor wheel. This is also the most expensive modification and costs over $3,000, not including installation. Turbo kits usually come with a software upgrade, larger fuel injectors to provide the proper amount of fuel, as well as any related piping or oil lines.