11,000 is very close to the revs usually turned with piped engines in CL stunt. An OS 40VF with a pipe at these revs (set at about 18" from the plug to the first baffle) is considered by the experts as having roughly the power of a muffled 60. In this application the pipe is boosting torque at around the peak of the torque curve which means you can turn a bigger prop. This is what was done with the old OS Hannos to make them turn a 12x12 prop (at even lower revs, something like 9,000). The other thing the pipe then does is if the engine tries to speed up when prop load decreases in a dive then it goes off the pipe and holds the revs more constant so it's a governing device as well.