i believe that stock vortecs are 170cc intake runners, now to what you mentioned. typicall 2 valve relief flat top pistons are about -4cc's now as long as you are setting your quench to about .040" then with those heads and those pistons you will be sitting at about 11.6:1 not 10ish:1. the experiment you are planning to do has been done many times before with all kinds of 305 heads, and to let you know they dont have 1.88" intake valves, from the factory those heads came with 1.71 intake valves. and those heads started off life as about 150cc intake runners with tiny exh runners, and if you do those heads it would be stupid not to use a dual pattern cam so that you have the exhaust valve open for longer to compensate for the crappy exh flow from the heads. back to what i was saying about a 383 with 305 heads, sure it will bump up the compression but you will be loosing so much top end it will be crazy, the 305 heads on a 383 wont be able to handle over about 4000-4500rpm and at that point the cam you chose would only be starting to make power.
i just reread you last post about the 305 heads flowing more than what a set of vortecs do, are you sure about that have you had them flow tested and if you have what numbers did you get, dont forget that head performance is not defined by maximum air flow, it is more defined as flow across the curve say .300-.500 lift as well as velocity during this time. when you go cutting a set of heads up you may be able to get the head to flow more air but you will loose velocity as you increase the cross sectional area of the port, this will drastically affect power from 2000-4500rpm where most vehicles do most of their driving
and your goal of 500hp is no where near realistic, like i mentioned before i think you will be hard pressed to even get 350hp from those heads, if people could just take a set of garbage heads and turn them into 500-600hp heads with just some machine work then that would be all people would do instead of looking for the proven performing GM head or a set of aftermarket heads. i have a something i like to day when i see someone trying to work a set of garbage heads here goes "you can polish a turd all you want but in the end you'll still just end up with a turd"
not trying to attack you but i still say that even though this is an "experiment" that these parts have been put together with absolutely no regard as to what actually works TOGETHER
Last edited by my87Z; 04-25-2010 at 05:46 PM.