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I used the Zenith cowl on a 750 cruzer with a lyc 0-320. Fit was pretty good except for the lack of space for the airbox on the 320. My first try : (the white cowl) was still short of room for airbox. So, I enlarged it again and now have the room and an air entrance for the airbox. (the same cowl, modified, and in primer.)
Ok....glad to help...this is what I did......
1. mount the cowl with engine carb and exhaust off. (no baffling)
2. decide the spinner you will use (I used a 13 inch Vans spinner kit)
3. make and install a plywood exact rear spinner copy bulkhead on prop flange (or, use the prop flange itself)
4. Cut the opening for the nosewheel strut, install the cowl, cleco together. Watch the gap at the spinner plate and keep cowl tight at firewall station. (Be aware of the motor offset to the right) ( and top plug clearance)
5. Now, install fasteners, and, with the cowl firmly installed, all fasteners tight, proper relation to the spinner plate, measure the distance from bottom of cowl to carb mount.
6. With cowl off, install carb and carb box air intake, measure the depth and you will know if or how much you will need to modify the bottom of the cowl (allow an extra inch)
7. Exhaust clearance can be cut later, last thing before paint. (Vetterman exhaust worked very well)
If cowl modification is needed, take lower cowl, and enlarge the bottom - photo will give a hint on how:
Glue urethane brown foam to bottom, carve and sand (sculpt) to proper size needed, glass over the finished foam block. Fill the contours with micro glass bead/epoxy mixture (I used West System) and sand smooth.
Turn over cowl and on inside carefully cut away the existing cowl material to just where your new fiberglass attaches to the cowl. Gouge out and remove all brown foam. Lay up several fiberglass layer strips as re-enforcement .
Note that my first attempt gave clearance for the carb and airbox, but did Not give adequate clearance for the rest of the duct work....hence the "snorkel" and a piece of 3 inch tubing to duct air to the airbox.
I used the compressibility of 3 in scat tubing to allow cowl removal - alum ring (ACS) was fit for appearance and screwed in to 2 nut-plates in snorkel. Take of the alum piece, unscrew the clamp holding the scat tubing on, and cowl comes right off.
Questions? just ask.
Super job Mark. pics are very helpful I'll gather up the materials and give it a go. Did you modify the airbox length or just attach the 3" tube to it and if so how? John
I used the same 3 inch ACS adapter I used on the cowl. I riveted it onto a plate made to attach to the air cleaner. Added the proper length + 2-3 inches of the 3 inch scat tube to be able to remove and "stretch" it to release the band clamp holding it to the cowl.. It also makes up for any misalignment and engine movement and vibration.