i have these notes from a previous thread....the horse power rating is most likely due to the chips were a tad different to comply with emissions laws
i watch that documentary every night before i go to bed.... ...never seen the special features part though...kool....There was no difference in engine calibration between '86 and '87. The engine made the '87 advertised power the first time they put it on the dyno for certification. They underrated it in '86 because Buick knew the Corvette was getting a 10hp bump for '87, and they held back 10hp in the published numbers so they could go up 10hp along with the Vette. It was all marketing.
If you have a copy of Black Air, the entire story is on the disc in the special features. A recording of a lecture two of the Buick Powertrain engineers did puts a lot of the myths to bed, and is fascinating.
I have a wh1..... very highly optioned.... touch climate, power seats, concert 2 sound, astroroof... I love the 86 because of the rarity... and in reality they all made the same power... a college near me dyno'd a 86 base model regal that was stock except a chip to keep it from detonating its brains out, and it made 298 hp and 367 ft-lb torque.... bone stock, i saw the pull and looked over the car... so if you want one over the other for the hp... you do a couple bolt ons and the 10 hp difference disappears! Just my two cents!If you want something special look for a nice 86 WH1 T-type . Same motor / trans as 86 & 87 GN , but only 463 made in 86 and none in 87 . I love the 2 tone paint .