i dont know anything about engines but i know a lot on car audio. first dont think of buying a bandpass box. each sub requires its own special bandpass box to play its best. besides over time the bandpass box will screw up the sub since its not designed for the sub. build your own box. it will cost you around $20 to build it yourself. i suggest making a sealed box. then get a jl audio 12w0. i have 2 of them and i broke my rear view mirror right off my windshield. i have to frequently glue it. a 12w0 will cost you $100. get a pioneer gm-x952 for an amp. it puts out 300x1 and sounds really good. you can get those off ebay for $130. you would have a sealed box, 12w0 and 300 watt amp for $250 total. you could spend more on carpet for the box and your wiring. that should put you right around $300.