Thank you all, for your helpfully replies.

Very interesting and curious the reading proposed by bem. In it, Hanno says that his top turtle deck is made with conventional balsa structure.[X(]
Also, Hanno states his no need for engine pump, very curious.
I think that the "multi little hole" solution (RFJ) and the "only a great hole" solution (dave), will be used according to the exact size of the engine used.

Finally, dave, what is the use of that silicone tubing that runs with the pipe and exhaust?