yes a b18a1 will fit in your car. yes you have to change the tranny. it is worth the change, but you should stay with something that is newer. like a k20, or an ls vtec b18. the horsepower gains are for the most part, similar, it just takes a little money. im not too sure what the horsepower stock on a d16y8 is, but a b18a1 is about 130. oh, and by the way, all b series engines/trannys, will all fit together and are interchangeable with parts.