if you also polish your intake and intake runs, if not the difference will be minimal. What that does is improving the volummetric eficciency of your engine - that means it will "inhale" more air for each cycle so then you can increase your fuel amount = more power. You will also need a larger throttle body (quite a bit of threads here about that) and a cold air intake with a high flow filter (otherwise there will be a bottleneck there). Once you do all this you can increase your fuel delivery by either larger injectors (lots of info about that on this site also) and/or an adjustable fuel pressure regulator (fuel return valve) - but here you are on a guessing game unless you use a wideband O2 sensor to monitor and log you air/fuel ratio. If your engine is not apart yet i would start with all the other mods before replacind valves and polishing intake runs. You can also add a performance cam as well if you rebuild your engine if you want to have even more power. Hope this helps.
