Will a 240sx transmission fit a sr20det motor?

Yes, a 240SX transmission can fit a SR20DET motor, as both components are designed for Nissan's S chassis. The SR20DET engine is commonly swapped into the 240SX, and the stock 240SX transmission (usually the KA24DE transmission) can be used with the SR20DET with some modifications. However, it's often recommended to use a transmission specifically designed for the SR20DET, like the Silvia or 180SX transmission, for better performance and reliability.