Well, both solutions are quite free so there is no restriction at least on normal carbs or mild tuned engines.
As I see it , K&N types draw air vertically which means mostly heated air from the block. On the other hand , foam types with the help of hood scoop can have more cold air , especially at high speeds which might benefit.
The only reason that i wouldn't fit foam type is the fact the carbs throw gas upwards that might dissolve or damage the material which certainly will drop back to the intakes. In racing conditions this might not be happening as before or after each race the foam is maintained and cleaned for optimum performance but this cannot be done for road use . In the few times i have left the K/N opened i could see the yellow mark on the hood and i had to clean it at some point.
Sprint 1.7 '85
Last edited by Greek; 07-12-12 at 12:32.