Here are some more numbers. Rossi R5 plug, Standard muffler, 15% Omega, 75 degrees and humidity of about 73%. Yesterdays numbers were with a humidity of about 50% and a temperature of 72 degrees. All readings were done without a spinner and safety nut only. I don't know if that makes a difference or not. I might try some more readings with the pipe and header I used on my Speed 50.

M/A 11x7 (for comparison of yesterday) - 13,900

All of the following are with APC props:

11x7 13,400 (I was hoping to beat the OS 55 with the Ultrathrust but I guess it wasnt meant to be. [])
10x10 12,240
10x9 13,350
10x8 14,350
9x10 15,100
8x10 16,320
9x9 16,200
8.75x8.00NN 17,800

More props of different makes:

Rev up 11x7 13,450
Zinger 12x6 11,250
Zinger Pro 12x7 10,230
Zinger Pro 13x5 10,740
TF Wood 13x6 9100

The new Webra carbs have a bore of .372" (plus or minus a couple of thousandths) as opposed to the .310" bore of the carb on my Webra Speed 50. When using the larger props a smaller bore carb would have helped a little I think.

An interesting side note. When I was testing props the first APC 11x7 I tested I only got 12,400. I tested it again in the middle of the rest of the testing and got the same results. Remembering David's comment about the RPM's I should get with that prop I tried a different APC 11x7 and got 13,400. I am assuming that the first prop was actually an 11x8 and incorrectly stamped 11x7. ???

OK fellows, that exhausts my usable prop supply for this engine. Your mileage may vary.
Rob