Hi shalo, O.S. makes more than one .15 buggy engine. There is even a large block .15. The best thing to do is go to the O.S. website and get the specs there. The car engines will not have any problem lifting the heli. They also have large heatsinks because when the car body is on there is not a lot of airflow over the engine. Do you also to have locate a clutch assembly? There are several makes that should work as well......with your choice of gear size.
Mark