2004 – 2007 USDM STi breakdown:
Rev. G (2007)
2007 US-spec Subaru Impreza WRX STi Limited. Only 800 were produced.In 2007, quite a number of changes were made to the US-spec model. Due to Subaru’s decision to reduce costs by cutting the amount of aluminum used, the US-spec STI no longer receives the J-spec Spec C control arms. The control arms are now the aluminum ones used on the Japan-spec revision A and B non-Spec C STis.
The high caster angle has been reduced, which in turn reduces the wheelbase from 100″ to 99.4″. The rear sway bar has decreased in size from 20 mm (0.8 in) to 19 mm (0.7 in). The gear ratios of second, third and fourth gears have been made longer (higher ratio) in order to improve fuel economy and driveability, which inadvertently reduces 1/4 mile drag racing times due to the ability to trap 114 mph (183 km/h) in 4th gear, without the shift to 5th. The EJ257’s cylinder heads have been redesigned to improve cooling, and the sodium-filled exhaust valves have been deleted. Pistons are the same as previous years.
The alternator is changed from a 90A rating to 110 amps. The rear Limited Slip Differential is now a Torsen unit, considered an upgrade over the previous model’s clutch type unit. The turbo has also been changed to the VF43, which has a different wastegate actuator than the VF39. The side cowl braces are stiffer than the 2006MY. The engine mounts are once again the hard rubber mounts used prior to 2006. On the interior, there is an audio jack that replaces the ashtray, a rear center armrest with trunk pass-through and a 120 W audio system.
The ECU was completely re-engineered in order to meet US LEV2 emissions requirements, which has caused throttle and timing issues. A secondary air pump was also added to help meet LEV2. Top Feed injectors replaced the Side Feed from the previous models.
The WRX STI Limited was introduced with fog lights, leather interior, lip trunk spoiler, and optional moonroof. It is similar to the Japan-spec WRX STI A-line, except the mechanicals of the car are based on the 2007MY US-spec WRX STI.
2004 – 2007 USDM STi breakdown:
GC chassis comparison to the GD chassis
Pros:
Subaru claims that the GD chassis is 10 percent and 82 percent stiffer in torsional and beam rigidity, respectively, than the GC chassis. Due to the increase in stiffness, the car has much better stability in corners and is easier to control at the limit.
In terms of safety, the GD chassis scored much higher than the GC chassis and earned a “Good” rating (highest mark) from the IIHS’s offset crash test. 4 stars front driver, 5 star front passenger and 4 star side safety ratings from the NHTSA.
In a magazine article from the December 2005 Firehouse magazine (a periodical written by and made for firefighters), Ron Moore writes how it is well-known that the Impreza chassis has great protection in its B-pillars. This side structure has 8 layers of high-strength, high-tension steel including a round steel bar running through the middle. The author notes how drivers simply walk away from horrific side-impact accident.
Cons:
One of the biggest complaints with the GD chassis is that it gains nearly 200 kg (441 lb) in weight over the GC chassis. Much of this weight came in the form of chassis stiffening as the car was made to meet every country’s crash standards. The weight also hampers the cars maneuverability, transitions and turn-in capabilities.
The GC Imprezas were notable for being very lightweight despite having AWD, the WRX Type STi Version VI, at 1,260 kg (2,778 lb), was lighter than the concurrent Mazda RX-7 type RZ (1270 kg) and Honda NSX type S Zero (1270 kg). In this fashion, the GC chassis has a better advantage. However it still remains at a slighter weight by shaving 200 pounds off of its biggest competitor, the Mitsubishi Lancer Evolution.