Complex sentence: This produced noticeably more power thanks to an increased effective compression ratio; however, Mazda engineers discovered that when changing the exhaust port to the side housing, a build up of carbon in the exhaust port would stop the engine from running.
Split into simpler sentences: This produced noticeably more power thanks to an increased effective compression ratio. However, Mazda engineers discovered that when changing the exhaust port to the side housing, carbon would build up in the exhaust port and stop the engine from running.