Complex sentence: Due to problems with the ASh-82M engines, the powerplant was changed to ASh-82FN making 1,380 kW (1,850 hp), but while reliable, the less-powerful engines caused the Su-12 to miss its top speed and service ceiling specifications.
Split into simpler sentences: Due to problems with the ASh-82M engines, the powerplant was changed to ASh-82FN making 1,380 kW (1,850 hp). While reliable, the less-powerful engines caused the Su-12 to miss its top speed and service ceiling specifications.