i own a 87, the year they made 53-55hp, the other years made 51-53hp, mainly a larger reed area, and larger tranfer ports. if you take a stock 87 against a 88-90 zilla, you will FEEL a difference in power betwwen the two, that is why the 87 cylinders crack when ported, the walls are already thin.i have raced shees, yfz's and 450r's at the strip,(i own a alky shee too) and i have never got beat by any other gas shee, a zilla hooks up unlike the tire spining shee, and it the zilla IS the fastest stock bike ever made in top end speed, .go on and race one on ashalt in the 1/8 mile and you will feel pretty dumb ,and the weight on them is 390lbs, 4 more than a shee!
the fmf pipe is a good around pipe for them, however they run alot stronger with a trinity outframe or ct pipe