Hey Tim , I getting 13,000 rpm's on an 12.23x3.75 apc on irvine 53 with stock muffler, fuel is cool power 15%. I have a few friends that run the irvine 53. you can see some here
www.theprofilebrother.com
I have several supertigre 45 with mouse can pipes that turn an 11x4 close to 15,000.
Hey I work at ew james in produce if you are ever in there. If you want to come over here and fly sometime , we are out on sunday's now that time has change.