1835cc is about 115ci and 2180cc about 133ci, Cont. A-65 170ci (O-170) When you go liquid cooled and propeller reduction the dynamics change but people seem to overdo it and expect to much with not enough displacement. It isn't a straight hp swap and I don't know what the curve or factor is but empirically it could be figured out with as much data as is available. I mean think about it put an engine in place of a 3600rpm 60hp that has to do 6000rpm to push 60hp and it obviously hasn't the same torque, and yes that does matter. You can use a smaller displacement engine but maybe to compensate to some degree for torque it has to put out 70hp (just throwing out a number) to be equal in reality, it isn't the same.