Most test bores used for the test in ? 4.060 that of a stock ls3.....340 to 360 cfm is typical depending on how in depth from porting...Hogged out 400's with +.125 bore size. What's spoke on in terms of porting is the norm...So, bone stock, #821's i'm coming up with 284 cfm @ .700 lift, 280 @ .600 this is using a 4" bore test plate. I have read people post much higher #'s. but this is on my antique bench, at 10" I have read claims of 320+ plus at this lift with this head? Don't get me wrong, 280 seems good to me at bone stock. And maybe there getting the bigger numbers with a 4.155 test plate.? So now on to some gasket matching, thin the guide boss down, some simple bowl blending and remove some funny bumps in the intake runners. Whats the norm on what i should be getting for improvement with such mods? Can I expect 25-30 cfm improvement?