well...no replacement for displacement. the b20 is going to move a lot more air and will give you the potential for more power down the line. if its a street motor just use a gsr or a b16 tranny. IMO the best tranny that balances economical fuel milage with good gears is the usdm itr tranny. same gears as a b16 with a diff. if u want shorter gears u can get the jdm r tranny....but i would not want to drive that on the highway.