SVX,

I'm running the 16D 18.6" 3-blade with a 120SP on my Corsair. I have the pitch set at 12". The 120SP turns it at 4660 rpm (9320 engine rpm). With a 90SP, I would think an 18.6" 4-blade would be a tough chore. Remember, RCV does not recommend going below 10" of pitch with the SP engines. However, I do think the 90SP would turn the 16D 4-blade hub with 16.6" blades. These engines will pull larger props than recommended by RCV. When the engines were developed, only the smaller multiblade props were available for testing. I would get the 4-blade hub with both sizes of blades and just try and see what performance you get from each. If you don't like the 18.6" blades, I may buy them from you. I've also had very good luck buying oversize props and bobbing them to the correct scale length and tip shape for my 60SP. I'm sure this would work for the 90SP if you feel you may want to run something between the 16.6" and the 18.6" blades offered by VarioProp.