It's small compared to a 400. Not comparing a 383 to a 318 but just saying that if you have the choice to build an engine that's externally the same but one has a larger bore, you do that.
I drive a 383 Magnum all the time in my '68 Coronet, it's nothing to write home about. Has headers, dual exhaust, "RoadRunner" cam, Performer intake, 452 heads... meh.
