Larry, I presume you have an O-200 in your Coupe? The STC for putting the O-200 in Coupes calls for the regular C-150 prop to be used. (Many installations on LSA eligible 415-C and 415-CD planes used that STC as "accepted data" even though they didn't actually use the STC to authorize the installation.)
On a Coupe, the pitch called for makes it a climb prop with a cruise of only about 108 mph but with quite good climb. Sorry I can't remember which pitch is called for in the STC. The first number is the length of the prop. The second number is how many inches forward the plane would move (with no slippage) on each turn of the prop. (Slippage usually runs around 5%. http://edburkhead.com/Ercoupe/enginepropeller_efficiency.htm ) Thus, a pitch of 50" goes forward farther than would a 48." The flatter 48" is better for the low speeds of a climb so it gives you greater climb. Ed
