I've never heard of an L series getting that high, and living to tell about it. You'ld have to have a NASTY cam, Forged pistons, completely perfect balance done on the lower end, Titanium valve train etc...Triple 45mm DCOE carbs, or some seriously adjustable F.I. But, I think you might not want to try to go this route, it's not a Honda...you don't need high revs to make power. There's alot of modifications you can make for some serious ass, Turbo, Supercharger, Cam, Exhaust, Ignition. Build the right Turbo set up, hit it with about 20 Lbs of boost...and the Honda boys on the street will never touch you.
well you find you a wrecked suzuki GSXR-1300 Hayabusa (you can have mine), yank that motor, duct tape it into your Z, and presto!! might even get 13k out of that motor. warren was right, it's not a honduh, or a motorcycle. you don't see tractors pullin 10kRPM do ya? that's cause they don't HAVE to go that high for power.
If you really want to rev high, and high for these engines is like 7-8k, there is all the forementioned mod's, and there actually is a cam by motorsport auto that claims to pull from like 6-8.5k, which is nuts. go for it, I'm not the one rebuilding every two weeks!!! Those engines that can do that are desinged totaly different, like an extra cam and an extra 2 valves/cylinder, and a really short stroke, and most importantly, about a litre less engine there. You don't need that 10000 to make some grunt. Besides, those 200 hp hondas have no tourq anyway, and tourq is what makes things happen.