well idk i just dont understand exactly why u couldnt chenge them out the whole point of the dual over head cam is so that one can work the intake manifold and the other work the headers but on a d-series engine its job is to work both but like i said there both 1.6 liter idk in my head it makes sense but yah any other ideas???
http://auto.howstuffworks.com/engine.htm
You cannot put a DOHC head on a SOHC block, they are completely and ENTIRELY different, sorry
Also, your car is automatic. Civics have crap low end torque and good high end torque, they are rev happy. Your AT transmission shifts before you get most of the power out of your car, so it's useless doing most/any of this. Only situations where I saw any real pull in my old '94 EJ1 with a JDM D15B AT (comparable to your D16y8 in terms of power) was when I was about 30 and put it in WOT and it downshifted and surged/pulled. But then it shifted right after it hit VTEC, and again, leaving me in the slow.
Want it to be faster? Go do a 5spd swap, then boost. You have a D-series, they are not made to be fast, but respond very well to turbo. Or get a b-series.
I think what people fail to realize is that Civics are economic gas savers, always have been, minus the Si. They are not made to be fast cars OOB or with I/H/E, it's the civic community that make them fast because we love our cars and like speed, and they are a great base to work on.
Anyhow, hope this helped.