If you can read japanese, you can get all of the jdm specs here: http://www.subaru.co.jp/impreza/wrx/

 

yah the different engine is a start

 

2004 Subaru Impreza WRX STi Sedan
Initial Specifications
Body 5-passenger sedan with blister-fender design
Engine
Configuration Horizontally opposed ("boxer")
Block Specially reinforced die-cast aluminum with integral cast iron cylinder liners, five main bearings, semi-closed open deck cylinder design
Cylinders 4
Displacement 2,457 cc (150 cu. in.)
Bore x Stroke 99.5 x 79 mm (3.92 x 3.11 in.)
Heads/Valvetrain Aluminum alloy cylinder heads with double overhead belt-driven camshafts (DOHC) four valves per cylinder, Subaru AVCS (Active Valve Control System) variable valve timing and sodium-filled exhaust valves
Compression Ratio 8.2:1
Horsepower 300 @ 6,000 rpm
Torque 300 lb-ft. @ 4,000 rpm
Fuel/Induction/Engine Management Resin composite intake manifold, sequential multi-port fuel injection (MFI) with multi-spray injectors and Tumble Generator Valves, electronic "drive by wire" throttle, high-boost turbocharger, intercooler and manually operated intercooler water spray

Emission Control System Low Emission Vehicle (LEV) standard, 50 state certified
Fuel Requirement 91 octane minimum
Drivetrain Subaru All-Wheel Driving System with DCCD (Driver Control Center Differential), Suretrac limited-slip front differential and mechanical limited-slip rear differential
Transmission 6-speed manual transmission with cooler
Gear Ratios *a little confusion-these gear ratios were supplied by Subaru-it was pointed out that 6th gear was missing
1 3.636
2 2.375
3 1.761
4 1.346
5 0.971
R 3.545
Final Drive 3.9
Chassis Unitized body construction with Ring-Shaped Reinforcement Frame structure, hydroformed front subframe and tailored blank-welded side sills and B-pillars
Suspension 4-wheel independent, sport tuned
Front MacPherson-type inverted struts with aluminum-alloy lower L-arms, liquid filled L-arm rear bushings, crossmember stiffener bar, coil springs, stabilizer bar and negative-scrub geometry
Rear MacPherson-type inverted struts with coil springs, crossmember stiffener plates, trailing arms, twin parellel links and stabilizer bar and negative scrub geometry
Brakes Power assisted 4-wheel disc with 4-channel, 4-sensor Super-Sport anti-lock brake system (ABS) with g-sensor; Electronic Brake-force distribution (EBD)
Front disc size 12.7 x 1.2 in., ventilated with four-piston fixed position calipers
Rear disc size 12.3 x 0.8 in., solid with twin-piston fixed position calipers
Steering Quick-ratio rack-in-pinion with engine speed controlled variable power assist, load-sensing valve and variable capacity power steering pump
Ratio 15.0:1
Turns, lock-to-lock 3.0
Turning Circle 35.4 ft
Wheels 17 x 7.5JJ BBS brand aluminum alloy
Tires 225/45ZR17 Bridgestone Potenza RE070 summer/directional
Exterior Dimensions
Wheelbase 100.0 in.
Length 173.4 in.
Height 56.7 in
Width 68.1 in.
Track (front/rear) 58.7 in./58.5 in.
Ground clearance 5.7 in.
Curb weight (lbs) TBD
Interior Dimensions
Headroom (f/r) 38.6 in.
Legroom (f/r) 42.9 in.
Hip Room (f/r) 53.3/51.9
Shoulder room (f/r) 52.7 in./52.9 in.
Trunk Volume, sedan 11.0 cu. ft.
EPA total interior volume sedan 98.6 cu. ft.
EPA class Subcompact
Capacities
Fuel 15.9 gal.
Engine oil capacity 5.0 qt. w/filter
Coolant capacity 8.1 qt.
Fuel Efficiency
EPA city mpg TBD
EPA highway mpg TBD

Go on babblefish and try to change the stuf from the *** site to english.