There is an interesting bit of detail in the Reducing Drag chapters of model design books.

There is an interesting picture of a number of various fuselages and their drag coefficients in the book "R/C MODEL AIRCRAFT DESIGN" by Andy Lennon. One shows a completely streamlined fuselage with an exposed upright engine sticking out in the breeze. It's just the fuselage, no gear, nothing but fuselage and that engine. No prop. And immediately under that is the exact fuselage shape with that engine enclosed in a speed cowl that actually tapers into the fuselage. Which should be a better situation than having the speed cowl standing out like a fin.

One has a Cd of .237 while the other has a Cd of .225