I tried to research this a bit, the info I can find is scarce. Assuming this has the stock 248 CI, The best answer is probably around 100 HP, maybe a bit more if this has been bored out. This is because wiki only lists the HP from 120-168 HP, for three different size engines, the 120 HP being from a 263 CI. The 248 bore/stroke specs: 3.0938 in × 4.125 in The 263 bore/stroke specs: 3.1875 in × 4.125 in It seems silly to me that no one seems to have the actual HP rating for this engine, good luck on your quest. -Jerry

Sources: Wiki has several- https://en.wikipedia.org/wiki/Buick_Special https://en.wikipedia.org/wiki/Buick_Straight-8_engine https://wikivisually.com/wiki/Buick_Straight-8_engine