VALVE / BORE Ratio 

The valve to bore ratio should be:
52-52.5% of the bore for Wedge heads. 
53-53.5% for Canted valve, rotated canted valve (Mopar P/S hemi) and true Hemi. 
If you decrease intake exhaust ratio down to 70-71% you can move both intake and 
exhaust valves over to the exhaust side and increase intake valve size by .5-1%. 

Anytime you increase valve size over the above stated Valve/Bore ratio you will see 
a small gain in CFM but the discharge coefficient drops and takes your power with it. 
An over shrouded valve instills a host of nasty scenario's, the two worst being 
decreased discharge coefficient and increased reversion below and above intake 
tuned power band.
(according to Darin Morgan)