If you can get 5% out of most 4 cylinder heads, without losing power elsewhere, you're doing a great job. I've tried them all over the years, and even the very best don't claim 20% (like Cosworth, for example). I'm just saying, keep your expectations reasonable at this point. I can tell you know what you're talking about from this and previous posts, but until you actually sit down and dissect a Honda head, it'd be pretty ignorant of you to make such lofty claims.

In any case, best of luck in your endeavor.