EJ20: This engine was stuffed into every mainstream Subaru car since 1989. This 2.0L engine comes in both DOHC and SOHC, open and closed decks, as well as being available in turbocharged and N/A formats. It has a 92mm bore and a 75mm stroke. This is the first engine of the EJ family to be produced by Subaru. It has proven to be a very durable engine in some variants, and temperamental in others. A good engine overall. The crankshaft and rods in these engines are forged.

EJ22: This engine comes in a few variants and was also stuffed into almost every mainstream car that Subaru produced in the 90's. Only TWO variants came turbocharged with closed deck blocks (EJ22T and EJ22G, which is a bored out EJ20G closed deck RA block). The rest, designated with "E" or "1, 2, 3" as the fifth digit, were all naturally aspirated engines. They all had a 96.7mm bore and a 75mm stroke, as they shared crank and rods with the EJ20 series. They are 2.2L. This engine series is known as one of the toughest to ever come out of Subaru.

EJ25: This engine is the overstroked/overbored variant of the EJ20 yet literally so different that it can be considered it's own machine. They had a 99.5mm bore and a 79mm stroke. The crankshaft and rods used were totally different from the EJ20's, the crank being heavier. This engine never came in a closed deck format. It DID come in DOHC/SOHC, turbocharged/naturally aspirated, and open/semi-closed deck formats. This engine was either REALLY good or REALLY bad, as it is known to develop horrific bearing and piston clearances over time, as well as blown head gaskets, which can create more trouble than one is willing to spend to fix.