Sometimes our airplane wants to be driven by another engine. Maybe it’s not quite happy with the available horsepower, the running characteristics, or the power system. When looking for the new engine it’s advisable to consider the dimensions in order to prevent a time consuming or even unnecessary rebuild.  
I have collected dimensions of aerobatic suitable engines for a long time. Some are taken from my own motors, some from my friend’s. Where not available the numbers came from manufacturers catalogues or websites. Since their designation of dimensions vary a lot, I have used my own specification ( based on the most widely used system ) given in the table below.  
         
A length
B overall height
C dimension from prop hub to front mounting hole
D longitudinal distance between mounting holes
E height above mounting lug bottom
F crankcase width
G lateral distance between mounting holes
H weight in Gramm
 

Dimension C "prop hub to front mounting hole" is seldom given in the specifications. However this number may be quite helpful when planning the modifications to the engine bearers. In some cases I had to calculate these from the numbers given by the manufacturer. I hope these were correct ! Also the weight numbers may not be correct down to the last gramm. These figures usually include an RC carburator, so the true weight of the engine ( and your airplane !) is a liitle less.
Engine A B C D E F G H
RoJett 76Re BSE 79,3 91,5 50,8 17,5 73,5 36 44,1 371
PA 75 85 89 51 21 71 36,7 44,5 349
PA 65 86,4 88,4 54 15 71 36 41  
PA 61 SE 86 87,6 52,2 15,2 70,5 35,4 40,8 318
Jett 61Re cast 83,6 107 50,8 17,2 87 36,3 43,7 320
Stalker 61 SE 95 95   20 75,5 39 44  
Super Tigre 60 86 96 52 21 76,5 37 44,4 356
Double Star 60L 85 102 53 21 78 37 45 300
Irvine 61 94 103 53,5 25 81 43,5 52  
Saito FA 56 104 105 51,5 15 87 34 46 405
Rossi 53 90     24 71 37,5 45 430
Magnum 53 85 85 52,5 17 69 33 42  
Magnum 52 85 89 53 18 70 32 45  
ST 51 81 86,5 49 19 70 34 42 320
PA 51 86 87,6 52,2 17,5 70,5 35,4 43,7 318
Jett 51 91 83 51,8 14,8 64,8 34 41 285
Double Star 50 78 91 48 15 70 33 41 244
Moki 50 90 90,6 50,6 25,7 72,4 35,8 44,4  
MVVS 7,5 86     18 69 35 41 378
Magnum 46 85 87 52,5 15 69 34 44 446
ST G 21/46 71,5 86,5 44,5 15 70 32,5 41 260
OS 46 VF 85 87 51,6 17,5 69,4 35 44 362
OS 46 FX                
OS 46 LA 74,5 84,7 42 17,5 70 32 40,5 260
Stalker 40/46 79 86   15 69,5 35 42  
Engine A B C D E F G H
OS 45 FSR 84 93 52 17,4 66,7 33 42 295
ST GS 45 83 85 48,5 19 68 34 42 377
Rossi 45 90     24 71 37,5 45 430
Thundertiger 42 75,8 82,5 43,5 17,4 65,5 32,5 40,5 252
Irvine 40 84,5 89,3 53,3 17,5 70.5 36 44  
Webra 40 GT 88 86   18   34   360
HP 40 GoldCup 78 79,5 45 17,5 63,5 32,5 39,5 250
OPS RE 87,3 86,5 54 18,5 69,5 34,2 42 316
Enya 40 BB 73   47 18 85 33,5 43 330
OS 40 FP 74 82 44 17,5 65,5 31 40,5 234
Double Star 40 62 86 30,5 16 65 31 38 190
Enya SS 40 73 84,5 45,5 18 68 33,5 42,5 286
Irvine 36 74,5 79,8 45,5 15 64 31,6 38 260
TT 36 Pro 74,5 75,3   15 59,5   38 313
ST G 21/35 72 83,5 46 15 67 32,5 41 270
Webra 35 75 79   15   32   268
Fox 35 57 83 29 16 62 30 38,4 182
OS 35 S 65 80,6 36,5 17,4 64,5 30,7 40,4 190
Super Tigre 35 67 78 41 15 62 32 41 232
Engine A B C D E F G H
Enya 35 65,5 82 43,5 15 65,5 32 42 226
Webra 32 75 79   15   32   268
OS 32 75,5 72,5 45 15 57,5 30 38 240
Magnum 32 85 72 47,5 15 61 30 40  
Enya SS 30 67   44 15 74 29,5 37 210
Magnum 25 77 78 42,5 15 62 30 38 297
OS 25 FSR 75 74,5 45 15 60 29,5 38 222
OS 25 61 71,5 35 14 57 28,2 35,8 165
OS 15 FP 56 63 31 14,4 50 25 33 132
Magnum 15 61 68 45,5 13 53 30 35  
PAW 15 61 66 29,2 23,4 53 25,8 32,8 180
                 
                 
You will discover a few empty cells. This is where I couldn’t find the respective data. If you happen to have these numbers available I’d be grateful if you can help to complete the table. Data of other suitable stunt engines can be added, too ( I hope the computer will cooperate with me ).