According to the road tests of my actual car when it was new in BMW CAR August 97 and Autocar July 97:
The engine is bored and stroked to give a capacity of 2114 by fitting different crank, rods and pistons, larger valves and modified ports giving:
170 BHP instead of the standard 140
0-60 7.3 seconds
Top Speed 139
I cant confirm these figure but did a rolling road test in 2009 which measured 140 at rear wheels.
In 1997 the engine modifications cost £5,653 plus wheels, suspension, exhaust and some other bits the Total cost of modifications was £7,228 on top of the price of the car.
I have never driven a standard one to compare.