Hi all; First post, 30 year subi owner.  I have a good short block 01-2.5 sohc.  I could buy valves and repair the original heads... But since finding this forum I'm hearing about using 2.2 heads.  Just so happens that I have 2 sets for sure and maybe another in the motor barn. All from the early 90's .I have read that they do not flow as well as later models, but slightly increase compression.  Will they bolt on and work ? I'm not wanting a race car ...(well at least not this one ) Just wanting to put together an extra engine on the cheap ,in case one of ours decides to be a problem. 

Works. People do it all the time. Search for Frankenmotor.

 

You need special head gaskets from Cometic or have to make some holes in a set of 2.5 gaskets for the coolant ports in the 2.2 heads.

 

This setup also requires premium fuel because of the compression jump.

They bolt on as a functional motor. If you use 90s heads on a 2001 block it will bolt into any 90-99 Legacy/Impreza and 97 Forester.

 

The motor will not be compatible with 2000 and newer without quite a bit of modification. (Double the workload if you want to make it work without a permanent check engine light)

 

http://www.ultimatesubaru.org/forum/topic/150509-97-ej22-into-99-forester/?hl=2000&do=findComment&comment=1263527

 

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Thanks for the reply's guys ; Modifying a head gasket seems easy enough but ...What is the difference in the heads that will cause a cel problem in a 2000 + ?  Everything (intake ) would be swapped from that year car. A lit CEL wont bother me on a car that is sure to have 200,000 + miles on it... but i'm curious how heads alone would cause an issue. 

The difference isn't so much in the heads as it is the intake manifold.

The electronics on the manifold (TPS, IAC, fuel injectors,etc) all changed in 99, and the manifold bolt pattern around the ports changed. Because of the physical differences in the manifolds and the sensors, you can't put a 99 or newer manifold on a 98-older head. (Not without a custom made adapter) Nor can you use the 98-older manifold with the 99-newer electrics.

 

The manifold has to stay within the year range of vehicle that it came from (90-98) or (99-04ish) so the wiring and electronics match. The heads then have to match the manifold.

 

 

A workaround for this if you want to bolt the 2.5 block into a 99+ car is to use 99-01 2.2 heads, but those are basically the same as the 2.5 heads anyway, so not much point.

Thanks Fairtax;  That was the information I needed.  I'll just fix the set of 2.5 heads .