Connect a spring scale to the tail wheel, hold the scale with one hand, open the throttle, see how many pounds of thrust the engine will pull....Have a helper handy in case your grip slips on the scale..

A normal G26 will pull 17 lbs at 9000 rpm with a Mejzlik 18-6 if the muffler is not too restrictive...The stock muffler is.....Only 8200 rpm....