you could start with the Jim McFarland formula:
Jim McFarland's formula for calculating the torque peak in and engine. The formula is: the smallest CSA of the intake track x 88200 divided by the cubic inches of one cylinder.

From MaxRace Software:
a more accurate Formula is

RPM = ( 614 * CA ) / ( Bore * Bore * Stroke * .00353 )

where RPM = point of Peak HP
614 feet per second (.55 Mach)

There is a whole thread on this here:
http://speedtalk.com/forum/viewtopic.php?t=771