Initial installation of the 200hp engine (slightly wider than 180 hp) in my Glasair-II resulted in contact between the heads of the two forward engine cylinders and the cowling. This required modification of the cowl to increase clearance. There are probably as many ways to do this as there are builders doing it, but I thought I’d share what I have done, for other’s consideration.
Basically, I fabricated a horizontal rib out of 3/8″ thick aluminum and screwed it to the cowl about 4″ below the cowl hinge line. Rib was cut to proper curvature (viewed from above) to flex cowling sides away from the engine. The rib is approximately 20″ long x 1/2″ wide, attached to the cowl from outside with AN-5078R10 screws.
Also I applied 1 to 6 layers of fiberglass to stiffen the cowl under the rib, to help prevent dimpling of the cowl at screw location.
Resulting in horizontal clearance from the engine is >3/8″, when the upper and lower cowl are in place.
See the upper cowling modification here.