there is 2 diff types of plugs..there is the ones with the lil crush washer on the end and then theres the ones with out..the crush washer ones are like a 1/4 of a turn after there hand tight and the others are an 1/8th of a turn.

you aint going to get 2% hp gain from just changing the plugs or turning one a 1/8th or 1/4 of an inche more.

hope this helps