I like to compete in the SCCA rallycross events here in Michigan because it is something to do during the cold icy winter when autocross doesn't exist. My winter/rallycross car is an '82 Rx-7 and while this is good when there is traction it is terrible slow in the snow and ice.
Being a devote rotorhead I hated seeing how slow the Rx-7 was and so after a year of thinking what to do, considering whether to convert the Rx7 like the Rod Millen cars or swap rotaries into an Audi Quattro, Geo Tracker, or Impreza. The Impreza looked to have the most potential and after taking many measurements at junk yards I bought a high mileage 1998 Impreza L AWD at an auction. The best thing about it is the body is in very good condition meaning very little corrosion.
So this is where I'm at with it at this time:
This shows S4 13B housings bolted to the oil pan with a turbo on for good measure! The more I get into this the better this installation looks. There is room in front of the standard radiator for the oil cooler, exhaust routing looks easy, no clearance issues if I run a turbo, and the standard S4 oil pan fits perfectly. I will need to modify the Subaru cross member so the rear edge of the sump can sit about half an inch lower. In addition engine mounts will need to be fabbed up to this cross member.
There will be issues with the S4 waterpump nose fouling the radiator but I wonder whether an FD pump would help because it is shorter. Also not sure if the alternator would clear the hood. Fabbing the trans/engine adapter plate and mounting the starter motor are going to be challenging.
This shows a 12A on the left and the 2,2L Impreza boxer engine side by side. Interestingly these engines are exactly the same length from transmission face to front pulley! Initially I thought only the 12A would fit but now with the 13B mocked up in position it also fits. Rather have the 13B for extra torque, parts availability, and ease of turbo installation.
Thanks for all the encouraging responses and thanks BLWFLY for the intake height measurements.
I need to place the hood back on today and check the clearance to see if a standard TII intake fits. Will also start mocking up the trans adapter plate.
If someone has an FD waterpump could they measure the distance from the face where it bolts up to the housing and the hub face where the pulley bolts on? This I will compare to an S4/S5 waterpump length and determine whether it will interfere with the radiator fans.
After mocking up an adapter plate out of wood and installing 13B dummy engine found there is about 7 inchs clearance under the hood for intake manifold. Elimination of one of the hood strengthening braces will give another 1/2" clearance.
Standard NA intake definately won't fit due to lack of hood clearance.
Took a look at how the engine mounting might look for the 13B
Next I'm going to install the adapter onto a half BP 12A and see how it looks in the engine bay. I think this engine would work well with a turbo and fuel injection. I like the idea of a top mount intercooler positioned in the std Subaru location with a WRX hood scoop.