I just flashed my gp1800 stage 1… 8300RPMs… on the riva site it says to go with the 13/20 solas impeller… Iv read online some people say 13/18 may be better… riva only says use the 13/18 for higher mods! Not sure which route to go! 13/20 solas still has great reviews!
Personally I’d go 13/18 and pitch tune it as needed. The 13/20 is a little tall for the stock tune.