Rev. E (2004)
This was the first Impreza STi model to be offered in the United States. Subaru unveiled this model in the Detroit International Auto Show, only 1 month after Mitsubishi announced the arrival of the 271 horsepower Lancer Evolution 8, which out-performed the 2.0L WRX.

The 2004 WRX STi is considered to be the lightest (3263 lbs, official brochure and tested by Car & Driver Magazine) and rawest among 2004-2009 models. The car was sold without a radio or floormats. The car was rated at 300 bhp and 300 lbs-ft torque, although many feel it was under-rated on purpose. What made the car so special to most is the level of performance offered for a mid 30 thousand dollars car, that still has a back seat and a big trunk.

Since its launch, many upgrades became available to increase power, handling and braking capabilities.

Some weak links were discovered in most 2004-2007 models since the 2004 debut. The IHI VF39 turbocharger wastegate may develop cracks that may or may not affect performance.

The oil pickup line inside the oil pan was shown to develop a crack leading to oil starvation and engine damage due to the lack of lubrication when the part fails. Several aftermarket vendors have addressed this issue by re-designing factory oil pickup units with beefier welds/materials.