Multiple Hybrid Equations.

[Alucard]

I'm going to start this off with the Phase 1 SOHC EJ22E's.

EJ22E Version 1 (90-96 EJ22E block).
Chamber cc: 41.
Bore: 96.9mm.
Stroke: 75mm.
Head gasket thickness: 1.3mm.
Piston cc: -14.5cc.
Deck clearance: 0.03mm
Compression ratio: 9.52:1.
Compression ratio: 9.82:1 w/1mm head gaskets.

EJ22E Version 2 (97-98 EJ22E block)
Chamber cc: 41.
Bore: 96.9mm.
Stroke: 75mm.
Head gasket thickness: 1.3mm.
Piston cc: -12cc.
Deck clearance: 0.03mm
Compression ratio: 9.86:1 (This is stock even though Subaru claims 9.7:1!).
Compression ratio: 10.2:1 w/1mm head gaskets.

EJ22E Version 3 (EJ22E head/EJ221/2/3 bottom. This is a hybrid that is not factory).
Chamber cc: 41.
Bore: 96.9mm.
Stroke: 75mm.
Head gasket thickness: 1.3mm.
Piston cc: -3cc.
Deck clearance: -0.03mm
Compression ratio: 11.27:1 w/1.3mm head gaskets.
Compression ratio: 11.71:1 w/1mm head gaskets.
Compression ratio: 12.03:1 w/0.8mm head gaskets.

The DOHC EJ22 hybrid approach is a bit more difficult with nomenclature as Subaru used different letters than "E" for each of it's 4 camshaft cylinder heads.
Though there were early EJ20 heads with pentroof chambers, we will be using the equations for the 46.6cc clover chamber heads since they are more plentiful and will be easier to obtain.
The EJ20 heads that possess the 46.6cc clover chambers are the following: Version 2 EJ20G (NOT to be confused with Version 2 WRX), EJ20H, EJ20R, EJ20K, Version 2 & 3 EJ20D, and USDM Version 2 & 3 EJ25D (along with Version 2 JDM EJ25D).
That being said, the Phase 1 head stage of DOHC EJ22 hybrid equations will be called "Stage 1 EJ22D" to keep things simple.
However, said particular hybrid can also be called "EJ22D, EJ22G, EJ22R, EJ22H", and so on to identify the heads being used on the EJ22 block if you want to go into detail within conversation.
Also, to keep things clear, no one should be using Version 1 (1996) EJ25D heads on an EJ22 block, as the chambers have a 99.5mm circumference vs the EJ22's 96.9mm bore.

EJ22D Version 1 (90-96 EJ22E block):
Chamber cc: 46.6.
Bore: 96.9mm.
Stroke: 75mm.
Piston cc: -14.5cc.
Deck clearance: 0.03mm
Compression ratio: 8.7:1 w/1.5mm head gaskets.
Compression ratio: 8.85:1 w/1.3mm head gaskets.
Compression ratio: 9.1:1 w/1mm head gaskets.

EJ22D Version 2 (97-98 EJ22E block):
Chamber cc: 46.6.
Bore: 96.9mm.
Stroke: 75mm.
Piston cc: -12cc.
Deck clearance: 0.03mm
Compression ratio: 8.92:1 w/1.5mm head gasket.
Compression ratio: 9.13:1w/1.3mm head gasket.
Compression ratio: 9.41:1 w/1.0mm head gasket.

EJ22D Version 3 (EJ221/2/3 block):
Chamber cc: 46.6.
Bore: 96.9mm.
Stroke: 75mm.
Piston cc: -3cc.
Deck clearance: -0.03mm
Compression ratio: 10.08:1 w/1.5mm head gasket.
Compression ratio: 10.3:1w/1.3mm head gasket.
Compression ratio: 10.6:1 w/1.0mm head gasket.
Compression ratio: 10.92:1 w/0.8mm head gasket.

This concludes Stage 1 EJ22D setups.