things seem a little slow before the holidays so thought i would throw this out.
two diff occasions  two identical planes, (two mouse 2 racers,and two Barten B Team racers)
 i built 2 identical upright pan based cyclon powered mouse racers with the ventures modified for suction the first one worked great the 2nd one would stall on take off .tried swapping motors ,same thing. i covered up the air intake in the cowl of #2 and presto ,perfect take off and the same top speed as #1
 Dave Platt built 6 Barten B Team Racers . all motors stock Irvine 25's on suction.#4 had the same problem as my M,racer.i talked him into blocking his air intake as i had done and the same results perfect take offs with good top speed
  i think there is more involved than just the size of the venturie but don't know where to start.