little more than 12 hp, stock si 108, stock 97 ex, 127 give or take 3. if you get the correct ecu it should work fine. but your best bet is to go with a z6 head and bolt it on your block. y8 will give you more compression than z6. i believe its like z6 = 10:1 and y8 = 11:1 or something around there with the a6 block. its all up to you weather you want a project to work on, let me tell you its an experience to change the head.