I have a 67 Mustang with a mild 351w underhood. I have recently been experimenting with different air filters, mainly a cone style filter adapted to connect up to a carb and the original stock style 14" round filter. I built up a little piece out of sheet metal that goes over the top of the carb (edelbrock 1405) and it has a 3" diameter inlet tube to it. I then connected a 3" diameter flexible tube to the inlet and ran the tube to a conical air filter located on the fender well. The conical filter has the same effective filtering area as the standard 14" filter I have always been using. Funny thing happened with the conical air filter setup, at high rpm's, past 4000rpm, it would surge and just basically lose all its umph. I thought "hmmm, I wonder if its restricting air flow?" I disconnected the "carb bonnet" and tried it again with no filter..... did the same thing, surge/loss of power above 4000rpm. I went back home, figuring I must have broken something, and put the old standard 14" filter and its assembly back on the motor and went out and tried it again. Goes like a rocket all the way to 5000rpm! Huh? I can understand that my design might do more harm than good, but shouldn't no filter be better than a standard 14" round filter?!??! What is going on? I am very curious as to what is happening under the hood. If anyone has any past experience or knowledge of this subject, I want your insight! I am just plain dumbfounded by what happened. And I repeated the tests atleast 3 times with each setup, and all the times with the conical filter and no filter it ran out of steam at 4000rpm, but with the stock filter it flew to the moon!