What does cutting the defuser ring off do?

[zx14]

say for a 27 cat I/0.
On a bravo prop

 

[hallett21]

say for a 27 cat I/0.
On a bravo prop

Taking it off reduces stern lift from the prop


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[farmo83]

The diffuser is to help keep water pressed up against the blade when the boat is coming on plane. After it's planed out it creates stern lift and drag as it's basically like dragging a mini trim tab. Cutting it off will make the boat have less stern lift, possibly faster, and in theory slower to break onto plane. I know Teague mentioned in his podcast on props you can add them or have them cut off of any prop(or at least he will).