I've measured the crankshaft and port timings on 34 of my engines and most sport type engines have the exhaust opening at about 75 degrees BBDC with the transfer at around the 60 degree BBDC mark (about 15 degrees of blow down). But this is just in general because there are some surprises. The Rossi 45 for instance is actually very mildly timed at 75/66 while an early ringed ST S45 is 80/60. Engines timed for CL stunt are generally around the 70/60 mark which, surprisingly, is what the venerable OS 40/46VF is. One engine I have (actually 2 different versions of the same make) have virtually no blow down period at all yet they're quite powerful.

Crankshaft timings though are all over the place and I haven't been able to find any rhyme or reason with them. Opening times vary between 32 to 50 degrees ABDC and closing from between 30 and 58 degrees ATDC but most have a total open time of about 190 degrees.