l do not care about the suspension because l do not plan on road or rally racing, I am just trying to figure out what the sti engine has in it that gives it the extra horspower the wrx does not.
as far as components. l know wrk has 225 and sti has 305

WRX=Turbocharged
-''Single''Active Valve Control System
-Aluminum Alloy Block & heads, open deck design, with
-cast iron cylinder liners
-Composite resin intake manifold
-Sequential multi-port fuel injection
-Redline 7000 rpm, speedomter to 150 (numbered to 140)


STi= Turbocharged
-Dual active valve control system
-Sequential multi-port fuel injection
-Alum alloy intake manifold
-Cast-iron exhaust manifolds
-Reinforced cast aluminum block, cast iron cylinder liners, semi-closed deck design, five main bearings
8000RPM redline
Speedometer to 160mph
(Basically the Sti is built to handle high boost)

Along with Michael is list, I'd like to add that the ST l has a larger blower than the WRX and appears to have a bigger air intake.

Nothing.

Biggest reason for the difference is the turbo. The VF48 in the ST l flows quite a bit more air than the TD04 in the WRX. They also have better flowing heads with dual AVCS(kind of like Honda is VTEC). Plus u get a virtually bullet proof 6 speed tranny compared to a 5 speed that u can not abuse nearly as much. DCCD in the ST l allows u to control the torque split between the front & rear tires.
And after reading the list above l am not sure where u r but in the US the ST l does NOT have an 8000 RPM redline. The block itself of the two cars r identical. Deffinitely does not have a closed deck block. We have not seen those since the early ninties in the 2.2 liter. l do not know where Michael got his info but lot is of wrong there.

if you r talking about the 2007 or 2008 model
the sti has the 2.5 engine and the non sti is 2.0

there is a sti wrx and a wrc the wrc is the rally car the sti is not as fast as the wrx the sti is more basic than the wrx the sti may look more dun up than the wrx but the wrx has a bigger engine and there for has more horse power and tourqes hope that answerer ur question