Thanks guys for your answer, at this moment I tried only an 18x8 on my sv26, the plane is a high wing of 84 inches and a lenght of 63 inches, the max rev I got is 6200 0r 6400 rpm at the full throttle, but nothing change from 60% throttle to 100%

In my hand now I get a 18x6 and 16x8, so I should try the 18x6 first?