Dick, the engines in the 421B are Continetal GITSO {Geared, Injected.Turbo/Super charged/Opposed} Ours are 385 H/P, Ram conversion. I can only remember two cases of intake ice when in non airframe iceing conditions in about 3000hrs on type, in order to see the ice inside the intake one has to get ones head way forward and look back into the scoops. Both times I recall took place in about plus two degC air temp when the precip was very close to turning into freezing rain. Hope this helps and check your PMs.