Just to compare the exit areas to what my 1955 Cessna 180 has, here are some photos. The 180 has cowl flaps which are VERY effective both for cooling and for speed.
Here's the inlet area. Pretty large, eh? Also notice the diverging duct to the large air filter. Somewhat spoiled by the edge of the lower lip, though.
Here's the cowl flaps open:
And again from the side:
Here's the cowl flaps closed. Note the relatively small exit area and the position and length of the exhaust pipe:
Here's what they look like inside the cowl. Note that the sides are effective even when the flaps are closed, to channel the air into the exit:
As you can see from the cracks and doublers, there's a lot of vibration down there. For reference, this airplane has about 3,600 hours TT.