[sperry]

Originally Posted by Kevin M

'06+ WRX injectors are the same (or really, really close) to side-feed STi injectors. Since '04 STi engines use topfeeds, and are smaller than side feed STi injectors, they are not directly compatible with any WRX injectors. So Scott is right, you cannot plug-and-play between WRX and STi injectors unless both engines are '06+.

The only reasons not to simply plug the STi manifold/wiring/fueling on top of the WRX long block (to get around the fueling differences) are the differences in the head, which boil down to AVCS and cam profiles as I understand it. Downgrading an engine, or pieces of it, is just never a good idea.

I don't think any STi <'07 has top feed injectors. There's a reason you can't swap STi block/heads under a WRX intake manifold. The WRX top feeds interfere with the AVCS solenoids unless you've got a Perrin fuel rail that will allow the front injectors to be clocked 90deg. That's why the STi all used side feed injectors up until the fuel rail re-design in '07 (IIRC).