Different transmissions require a different bellhousing to allow correct installation. It is bolted to the engine block and contains the flywheel and clutch assembly or the torque converter for the transmission. The transmission is then bolted up to the bellhousing to complete the installation. The starter motor is usually mounted through the bellhousing as well engaging with a ring gear on the flywheel or flexplate. The Bellhousings are available in different materials OEM style Aluminum or Heavy Duty Steel SFI approved for racing.