Here are some, starting with a little Diesel: (all in C.I.D.) and a maybe why?
.009,
? tooling?
.010, .020, .024, .039, .045 tooling, power, .010 was the hottest engine of any size by hp/cu.in. for quite awhile
.049, .051, Free flight classes, .06
?
.061, 1cc
.074, .075, .09, .098, .099, .10, sport power
.11, .12 probably cost.
.14 Herkimer- who knows???
.15 convenient size, 2.5cc
.19, .201 Free Flight class
.20 sport power
.21, 3.5 cc
.23 O&R
a convenient size?
.25, sport power
.26 probably power in a small case
.28 probably power in a small case, sport flying
.29 free flight class
.30, .31 free flight class
.32, .36 two engines in one size case
.33 O&R?? Johnson SS?
.34 Garofoli wanted more power in a 21 case
.35, .8 x .7 bore and stroke Fox Stunt
.36 combat class when some engines came out in slightly off sizes.
.40 more power for sport RC RC Pylon
.45, .46, .48, .49, .50, .51, .52, .53 .56, .59 more and more power
.60, .61 FAI class 10cc
.65, .70, .72 .74, .99, 1.08 power, power, and more power, mostly RC
Just as an aside- it seems when motors were built in different sizes in one case casting the smaller displacements seemed better suited for high rpm, the larger bores better for easy handling
Fox 29-35-40 Supertigre 29-35-40-46 and others.