The 185 horsepower from the Olds 403 sounds meager—especially for a Trans Am—but few other contemporary engines were making more power from similar displacement.Click to see full answer. Thereof, is the 403 Olds a big block?403. The 455 “big block” Olds V8 was replaced in 1977 with the 403 cu in (6.6 L) “small block” V8. It used a wide 4.351 in (110.5 mm) bore, the largest ever used in a small-block V8, with the Olds small-block standard deck and 3.385 in (86.0 mm) stroke. what is a 403 engine? The Oldsmobile 403 was a pretty short run engine produced from 1977 through 1979 and while it appeared in some performance minded cars of the era like the Firebird, Buick Riviera, and Olds 442, it has never really been looked at as a serious performance engine but the larger hot rodding populous. Also, is the Olds 403 a good motor? Most of us would like to keep the Olds 403. With what you guys at Car Craft have done before with other oddball engines, we know you could build good horsepower and great torque. The stock Oldsmobile 403 enjoys the benefit of a giant 4.351-inch bore diameter with a relatively short 3.385-inch stroke.How much horsepower does a Oldsmobile 307 have?It has a peak horsepower of 230 hp at 4,600 rpm. The engine has a peak torque of 285 ft. -lbs.