i fitted a 328i into the ti and kept the standard 318ti gearbox. i used a 325i intake manifold and had a remap as the 328i was from an automatic car. it cost very little goes really well and pulls like a train. where i live they close part of our town centre to let us drive around a short circuit to promote motorsport. this is a clip of one of the demonstration runs when the 328 engine was fitted (i have gone back to the m44 now)
https://youtu.be/T3ORxdwVY2E