I have a 94 WRX and Ive just bought a forged 2.5 with STI V5 heads which I plan to throw in, now I know my present management and most of the ancillary components aren't compatible with these heads. I need to know what my options are, do I stick with these heads which would require a fair bit of modification mechanically and also to the wiring loom, is the wiring loom from ecu to the 2 grey plugs on the N/S inner wing separate from the main wiring loom?

Or option two, do I swap to STI V4 heads? I believe they are the ones to have? I also have a spare set of 95 UK turbo heads, could I swap the cams, valves and buckets from the STI V5 heads in to these with a little porting? Would these heads need any other modification to make them compatible with the 2.5 bottom end?

 

from what i remember the version 5 had solid lifters not sure if the v4 had them as well,there was a reason i couldnt use a V4 bottom end on my V5 heads but pm david@api and he'll point you in the right direction

 

You could.

1) Use version 5 heads and have your existing manifold cut and welded to suit.

2) Change the heads for phase 1 -1.5

It’s also not just a case of swapping the cams etc this won’t work as there are differences between the two phases. Also the heads are shimmed not solid


Failing that you could possibly adapt the version 5 engine loom to your car but this would depend on your ecu and other things would need to be considered. Not a very straight forward option.

 

Im leaning towards STI 2,3 or 4 heads, Im not to keen on adapting the engine loom to accommodate phase 2 stuff. I plan to use and early Apexi for the management, cutting the std inlet to fit sounds interesting, who could make a proper job of this?