The engine is a wide deck angle valve. The plans call for buying the cowl - with no cowl available for my engine scratch build is a reasonable deviation from plans. Below I show that this is _not_ efficient or cost effective; if you can use the Aero Composites / Featherlite cowl, by all means do so. I had to start with the requirements. The cowl has to - provide a streamlined shape to the fuselage, - have a stiff and resilient surface durable enough to handle the proximity to prop wash and engine vibration, - be secured with reliable and easy-to-remove fasteners and - facilitate engine cooling, with efficient and properly sized intake and exit areas. Shape and Fasteners. Cowls should have minimal drag and ideally complete an airfoil shape over the fuselage. I've chosen to have a) an upper - lower join that matches the wing trailing edge, b) a boat tail on the lower surface, and c) exhaust exiting through an "eductor", an effort to have exhaust gases pull air through the cowl. I secure the cowl to the attachment flanges built into the wings and fuselage. I will use Dzuz fasteners every 4 inches on the top and bottom arch, and piano hinges at the wing-cowl mating surface. This is contrary to the builder group discussions, which prefer Camlocks. I have 85 year old Dzuz still working well in a PA12, and I'm comfortable with the simpler install - I'll go with Dzuz and use more of them. For the long straight joins I'll use my RV experience and go with piano hinges. I'll pay up for the extruded hinges, just in case it's a strength issue. Construction method. The shockwave of prop passage will hit the cowl surface at 2700 rpm x 2 blades = 5400 times a minute, 90 times per second. The closer to the prop the harder the hit. To handle that force I decided to make this cowling from carbon fiber cloth with a Coremat center. This is consistent with a presentation for the Cozy builders group. The presentation is at https://docs.google.com/presentation/d/1vTyFMM8RQ9PijpZ07AT6vDHU164KCHXY/edit?usp=sharing&ouid=111349802257488370268&rtpof=true&sd=true Intake area. Per _Tony Bingelis on Engines_, the rule of thumb for inlet areas is .35 x engine hp (p.87). At 200 hp, my IO-360 should have an inlet area of 70 in2. The cross section at the end of the ramp of the NACA inlet is 15 x 2.75 = 41.25 inches. Unless the NACA in nutty efficient and has an effective area 1.7x the cross section, I need another 30 in2. My oil cooler has a face of 30.8 in2 - if I feed the cooler with an armpit scoop sized to match the inlet area is 72 in2 and on target with the Bingelis guidance. But most Cozy fly without the armpit scoop feeding the oil cooler. I will build and make initial flights with no armpit scoop, knowing I can add one. I will focus on having an efficient NACA intake, using the corner tabs that keep air from tumbling out of the intake. Exit area. I have not found a standard for outlet area. Per Bingelis the outlet is at least equal to the inlet. Per the Vans forums it should be around 1.6x the inlet area. Above I plan for 72 in2 of intake, so I target an outlet of 115 in2. The area around the prop flange is a diamond of total area = 119, less the area of the extension prop flange for a net 80. My exhaust pipes exit through the lower cowl; I am shaping my exhaust pipe exits as eductors, hoping they will pull air out of the cowl. The area of the eductor is 23.8 in2, less the area of the exhaust pipes is a net of 17 per side = 34 total. Total exit area is 114 in2. On target. Construction steps. 1) Install the (purchased) exhaust on the dummy engine, and any eductors. If not done already, install the cowl mounting flanges, keyed to the expected thickness of your cowl. Wrap the engine. (Eductors are a lower cowl feature, and need to be fitted and secured before the lower cowl layup. I determined the target radius and pop riveted stainless steel shim stock. I then wrapped this in a sandwich of fiberfrax, CF+ Coremat + CF. I let the epoxy set in a frame that gave me a targeted oval shape, matching the exhaust pipes.) 2) Mount the prop extension - the cowls will need to converge and terminate 1-3 inches forward of the mounting flange. The front face of the extension is the back face of the prop. 3) Mount the wings and copy the edge profile required at the cowl-wing join. Securely attach the profile to the spar, but knowing it will be removed after final cowl casting. Remove and store the wings. 4) Surround with foam STRIPS. The cleaner the curves of the foam strips the less time and money you will spend on filler. [A better approach is to build a cardboard shape, then fill around that with the foam.] The cowl is laid up on a casting surface, and the better the surface the better the cowl. Plaster and sanding, epoxy squeegee on the plaster, then packing tape. After all this work I finally have a good casting surface. 5) An armpit scoop was laid on a core carved from a block of pour foam. CF + Coremat + CF for the scoop. This will be held in reserve for use if required. Materials: 4 sheets of foam sheathing @ $28 each = $112 6 cans gap fill = $24 2 gallon kit of pour foam x 2 = $125 x 2 = $250 1 quart PVA = $26 1 tin miracle glaze mold release wax = $22 10 yards 3k 4hs carbon fiber (needed 7, bought extra) = $182 (Soller Composites) 5 yards CoreMat XM = $0 (the manufacturer sent a free test roll) 1 gallon West resin + extra slow hardener = $120 + $60 = $180. I buy this as I run out, and it was time to get more. 1 gallon acetone to clean arm hairs of gap filling spray foam = $25. As with the epoxy, buy it when in runs out. Total ~ $825. Chris at Aerocomposites offers a full set for $650 - if you can use a purchased cowl, it's the smart way to go! https://aerocomposites.aero/