The parts listed on that "upgrade" will not give you 430 hp !! Xcceleration is xagerating the hp improvements. First of all, the US Spec '04 STi has a couple of limitations : the injectors are only 480cc and the turbo is good for 370 hp (turbos are pumps and as all pumps they have limits as to how much volume they can circulate). This is from a very reputable company that bases its claims from detailed dyno runs and alot of research. You can get alot of info from their site - you probably have heard of them : www.aps-wrx.com they go a bit more in-depth than most other companies so it's great info. I have been following the updates since I talked to one of their engineers at a meet in California - he was very informative as well. Now - their prices are xtremely high :-( it will cost you about $9000 in parts + whatever installation the shop charges you + you have to "tune" your car on a dyno ! I'm going to start saving soon .. so I can afford the 400 + hp upgrade for my '04 STi !!
Hope that helps
i agree with the engineer...i found out that they dyno'd the car in second gear only......it needs to get to fifth gear for an accurate measurement.....just got back from being dyno'd at my shop....272 hp at the wheels(up from 245 base stock) 285lbs torque...i thought it was fast before!!!! remove those cats and see what happens....BAM!