8:1 sounds very low for the -9. That's closer to what the short-wing RV's get.
The Cafe Foundation report is probably the best place to start...
http://cafe.foundation/v2/pdf_cafe_apr/rv-9a.pdf
They measure it at about 12:1.
There are so many airframe/engine/prop combinations. Further, in amateur built, no two are the same as in type-certificated aircraft. Therefore, the only way to know for sure for YOUR airplane is to go and test it. Then enter the data into your POH.
Bevan
Thank you. The link would not work, said I didn't have permission.
Go to http://cafe.foundation/v2/main_home.php then click the "RESEARCH" tab, then on the right side menu click "CAFE APRs" and choose an aircraft.