I planned to use a pitts style muffler and let the exhaust stacks extend out of the bottomof the cowl like the full scale. This is the G-17 model. This model has a cowl vent flap on the bottom of the fuse just behind the firewall. You hardly ever see it in all of the photos on the internet unless you are looking for it. This will require a "tunnel" cut through the firewall about 3 inches wide and about one inch high. Since there are no external vents on the cowl (G-17), the tunnel will also serve to ventilate engine and muffler heat from the cowl. It may not be enough so the hole in the side that is cut for the OS 1.20 valve cover may be used for additional ventilation.

I may just install the cowl vent on the bottom of the cowl (only 2 inches forward of the scale location). This all depends on how close to scale I want to get. If you are building a D-17, there are other vents on the cowl.