Bro, in the first place are you going to register it after changing your engine. If you are, than you are in for trouble as Puspakom will not approved it. You can only increase power to a car not more than 25% of the present cc. Therefore if yours is at 2000 cc at the moment, the maximum you can do it would be a 2.5 litre BMW engine. that too you will have to write in to JPJ for approval.
Now if you are NOT intending to do all of the above but just keen on getting a bigger cc, than be prepared to face the full law when you do get into trouble in the near future. As for a good mechanic, who does well in conversion, i would recommend Blue Green Motor Werks, based of the federal highway after the Sunway double bridge heading towards Subang on your right hand side of the federal highway.
I have done my conversion there and i am satisfied with their werks. :cheers: