Complex sentence: Although superficially similar, it was longer and heavier than the A40 Devon engine with the advantage of being bored out, whereby the piston cylinders diameter was increased to provide a larger capacity if needed.
Split into simpler sentences: Although superficially similar, it was longer and heavier than the A40 Devon engine. A major advantage was that it could be bored out, whereby the piston cylinders diameter could be increased to provide a larger capacity if needed.