When it comes to EJ22s, there are 3 Phase 1 variations here in the USA.
They are also all SOHC as the USA did not get a DOHC version. Ever.
All have the same bore, stroke, & forged internals (rods, crank) with slight differences.
These engines have open decks, SOHC, & dual exhaust ports per head.
Pretty problem free for the most part of they're taken care of.
They share rods w/Phase 1 EJ20s & EJ18s & generally produce about 130-135bhp.
Compression ratio is about 9.5:1 max.
The 2.2 engine was further upgraded with higher compression, molybdenum coated pistons.
They also received valvetrain changes in the cylinder heads to reduce friction & single exhaust ports per head.
The block is open deck, the same as the first EJ22E.
The piston crowns in these engines are different than those in the earlier variations.
The compression ratio in this variation is about 9.7:1 max.
It produced 135bhp but there were a few dual ports produced in 1996 as Subaru was overstocked w/EJ22s @ the time of mass production.
The only turbocharged variant of USDM Phase 1 EJ22s.
These have closed decks, piston oil squirters, deeper dish pistons, slightly thicker rods, & their heads are drilled/tapped for turbo.
The camshaft has a profile that's set up for turbocharging & the valves are smaller than that of the 22E variant.
These are very strong but like all other things, can & will be destroyed if they are put under too much stress.
Now onto the EJ25D.
We got 3 variations of these in the USA (the last variation actually being a cross between Phase 1/Phase 2) & they produce 155-165bhp.
They have larger bores & higher strokes than the EJ22 along with thinner piston rods that are NOT forged.
As such, they naturally produce more power & tq but are not nearly as reliable due to their habit of blowing head gaskets like its their job.
The cylinder heads are variations of JDM heads but have lower RPM limits & lesser valvetrains.
These came equipped in 1996 Outbacks, GTs & LS/LSi & were bolted to an automatic only.
They could not be had any other way.
The 25D of this year had 9.5:1 compression, domed head chambers which were cut to the bore of the block, & high compression pistons.
These did blow head gaskets but not nearly as much as their later variations.
The cylinder heads had hydraulic lifters & larger intake ports than its later variations.
This engine made peak tq @ 2800rpm, which I personally think is awesome.
The peak bhp was 155 max.
This engine recieved changes to its valvetrain, Subaru got rid of the hydraulic setup to produce more power at higher rpms but lost the ability to produce peak tq @ low rpms.
The chambers are cut into clover shapes & are not domed as the earlier variant was.
The intake ports are larger than that of the 96 DOHC heads.
The pistons are also deep dish & square cut.
Rods & crank are the same as the 96 variant.
These were prone to head gasket leaks, which would lead to compromised & destroyed internals.
These were now in autos or manual transmission equipped cars.
Peak bhp is 165 max.
The factory "hybrid."
It has Phase 1 1997-1999 heads on a Phase 2 block with 1996-1999 internals (pistons) but the crank is Phase 2.
Came in auto or manual transmission equipped cars.
This engine produced the same power as the variant before.
Peak bhp is 165.
All EJ22s have 52mm rod journals & all EJ25Ds have 48mm rod journals.
This is the gist of what you're working with when you're dealing w/Phase 1 USDM EJ engines.
This is all of the general info that I have been able to gather from personal experience as well as others who have worked w/Phase 1 Subaru EJs. Don't let the horizontally opposed architecture of the engine surprise you. It's actually a really simple concept. Just another 4 stroke engine with an extra cylinder head. That is all it is.
I also request that this bit of information be stickied so that it is easily accessible at all times so the new guys know what they've been introduced to. I'll get onto hybrids in a short while.