Troy/Frank,

If I may...... In Sacramento we're racing warbirds with these motors on 20-30% nitro and APC 13x13N props. The RPM's are a little higher than Troy's recommendation of 9.2K-9.5K, but for the most part I've found that the motors will turn this prop about 10K-10.3K on the 30% fuel and they seem to run very well...... this is using the header set up as well.

Hope this helps.

Jimmy Skids