AdrianM

this comming season in the UK we are running 19T Stock one day and Mod the next,some of us have been practicing and the different types of 19t motors have been from 47mm per rev to 54mm (sorry not sure of rollout in inches).
Bear in mind this is indoors on carpet,the difference in lap times between mod and stock have been minimal.
Hope this is of some use to you.

Alan