Dan Olsen wrote:

I’m early in the stages of building my IV-P (piston) kit and am looking for advice on whether I should use the standard e-glass cowl that came with the kit (circa 1997) or if I should pay to upgrade to the carbon cowl.  I know there will be some weight savings.  Do any of you know how much?  Are there any other differences or advantages for the carbon version?

Dan,
I have a carbon cowl on my IV-P. I just looked at Bill Harrelson’s almost-completed fiberglass cowl on his IV. They are both effective, and the weight difference is small. (a couple of pounds?). For my money, the carbon cowl is not worth the extra money if you already have the regular one. There are a  couple of things you should do to either cowl—assuming you are using screws, Dzus or similar fasteners to attach it to the fuselage: First, put a two-inch strip of 2-3 bid carbon or fiberglass inside the back edge of the cowl where it meets the fuselage. This both strengthens and adds thickness where the fasteners penetrate. If you plan to use Dzus or screws to attach the cowl, countersink stainless Tinnerman washers (available through Aircraft Spruce) at each screw hole flush with the surface, and overlay with 2 bid of carbon or fiberglass. This will make the hole/fastenings almost permanent. If you just countersink and fasten through the fiberglass, it will wear through in a thousand hours/thousand removals or so…

I used regular aluminum hinge to tie the top and bottom cowl parts together. Carbinge works well also, but if you use screws, you’ll want to use the same treatment above on this area.

My two cents…

Bob