im trying to make a ringer d15 for our shop that we can say is all stock factory parts... dont ask. So are there any differences in head design from one generation civic to the next? Is there any advantage in using a newer head? We've heard (heresay) that newer heads are more efficient, as they make similar hp numbers as the older motors, with a smaller cam. Is this simply compression making the difference, or is the head actually better flowing?