I notice some differences in the top silhouette of the RV4 cowl. Referencing the picture below, the left shows cowls that bulge on top, and the right shows cowls with a smooth transition. I wonder what this bugle means, if anything. Are their different cowls for different engines? I just don't see how this variation can be achieved if all cowls are the same, unless some engines have a higher crankshaft centerline, or the instrument bay cover is angled differently? For what its worth, 2 examples I know of with a bulge have o320-D1A. I understand that these aircraft are all hand built and all different, but even with respect to that, this variation seems strange, as if an engine was installed higher, or leaning upward slightly. I have seen stronger examples of the bulge, but I can't seem to find pictures. Yes a fairly unimportant topic, but I am curious.