I just used this page for air velocitiy in the pipes :
FLAT4EVER.COM - VW Aircooled Cox Coccinelle Karmann-Ghia Volkswagen Buggy Beetle - Calcul de la Vitesse des gaz
it is made for Beetle engines so I had to convert my valves equivalent surface to a single valve equivalent.
Anyway, going from 72mm bore to 79mm bore (DR 350) meant an increase from 76m/s to 92m/s @ peak power (as well as an extra 50cm3)