what exactly do you want to know? you'r going to have to read through pages of shit to get a real answer with such broad questions...

98 - 2005 wrx has ej205 not quite sure on earlier models.. somewhere there was 1.8l??

98- 2005 STi has ej207

2006 wrx on has ej 255


2006 STi on has ej257

207 are probably known as the strongest. 257 are bigger, potentially more power but are a bit weaker.

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Twin scroll Pig Bi-Squeeling