With the kind of drag and weight air boats have you may need to go up a size or two to get your 40+ mph.

The size and weight of these .90 class engines is not much different then the .60-75 class. In fact the G90 uses the small crankcase. The O.S. weighs less then other brands .75's.


For the PRICE and POWER you will have a hard time doing better then a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXFV79&P=0]G.90[/link] from Super Tigre.

It will turn a 13x9 at 12000ish on the ground once fully broken in, running 10% nitro.


If you are wanting more RPM it will cost you more. An O.S. 95 AX will rev higher turning even bigger props. I have seen the AX turn a 14x8 at 13,200 on the ground. That is impressive.

http://www3.towerhobbies.com/cgi-bin...?&I=LXXMU4&P=0

Either one of these engines with the right prop are going to get you real close if not over your speed goal.

Another option would be Thunder Tiger PRO in the 90 range. I am not real sure but I am guessing it is somewhere in the middle between these two.