Sonnax turbine hub FD-HT-33HS has an updated design that improves oil flow for piston release for 4R100 units. On the factory 4R100 converter piston, release oil flows between the needle bearing and front cover. A large amount of bearing clearance is required for the oil to flow outward and release the piston. The Sonnax turbine hub has been designed for improved piston release flow. The oil exits on this hub on the outside through angled holes, like those on the 5R110W turbine hub. The needle bearing clearance can now be reduced to improve bearing life.