Can you use a 525i engine in 325i?

No, you cannot use a 525i engine in a 325i. The 525i engine is a straight-six engine, while the 325i engine is an inline-four engine. The two engines have different dimensions and mounting points, so they are not interchangeable. Additionally, the 525i engine produces more power than the 325i engine, so it would require modifications to the 325i's driveline in order to handle the increased power.