wye/delta switch on q100h?

I am powering a q100h 260rpm (on the front) with 48v and 20amps with a Kuteng controller. Already for several years, running fine.

I am achieving a top speed of around 40km/h on 700c wheels. I see that, at that speed the wattage drops down to 400-500W (from around 700-800W), due to the battery voltage and back emf.

I am thinking how to get a better speed with the q100h. Would a wye delta switch help on this case? or I misunderstood how it works?

Thanks!