[Ranma]

There are a lot of reasons for an under preforming engine. You need to do a check of the engine to see what could be causing it. I have a 7MGE and it does ok for my needs. I am not destroying my car in the juvenile and so male thing of drifting. My guy performs best at about 4200 rpms and does not like to run under 2500 or so. He gets very slug like doing this.
So you need to do all of those things like checking pressure in the cylinders, spark plugs and all of that other stuff. I would suggest buying a good repair manual for your car. It will help you perform all of the diagnostic tests. Just changing out the engine is probably a waste of money.