The G90 with the one piece crankcase with the larger rear bearing and the smaller intake passages is considered to be the lugger. But I still like the 14-6 or 13-8 on the G90's. I've tried the 15-8 and 16-6 on them and they perform like the book says but spool up from idle is slow. They would perhaps, work 'OK' in a scale situation where you were trying to get out beyond the cowl. I get 11,000 with a 14-6 APC and the 108 carb. The 40 carb only gives you about 10,000.

The S90K is the one you are talking about with the two piece crankcase and the squarish head. They look somewhat more massive than the G90.

The S90 is the one with a crankcase a lot like the S90K but it has a round machined head that is sunken in the middle.

The last truely Italion made G90's to come from Italy had a '40' carb on them for some reason. They do a lot better even with the big props when using a ST carb with the flat sidded spray bar or by using a Magnum 108 carb which bolts right in.

They all seem happy with a 14-6. prop

In a diesel situation, the round sided spraybar '40' carb would be better.

Enjoy,

Jim