The elliptical inserts move the incoming air over to the side and over the spray bar, to help with low speed/ off idle runability...

I have been using the Nitromizer inserts for a while and did notice that with the normal insets, cruising around at just off idle, the engine loaded up. Now, this isn't ideal during a race to drive like that, I just wanted to see if some of the claims were true..... and they were