Engine Cover & sundeck

Alright so my 1986 Celebrity 210V is getting lots of works done on her... I've ripped out all the rotten interior pieces and I have to re-build my engine cover and back seats. How much room do I need to leave from the top of flame arrestor/carb to the bottom of the cover? I was thinking about 3"-4" between them.. Is this enough? I was planning on building it out of marine plywood and covering with upholstery. Any ideas of sound dampening materials? Any other suggestions on this project? Thanks in advance....

 

They usually don't draw air from the top so you only need clearance to keep the cover off anything if it flexes when someone stands or jumps on it. Make it as light as possible but still able to withstand the above. The foam-lead-foam sheet stuff works OK, padded upholstery helps. Filletting the inside corners, rounding the outside and FG taping both makes a strong cover without the cumbersome framing, but does interfere with stapling the upholstery so you have to plan ahead.

 

Ditto what Sam said. Engines run a bunch better if they can get a cold air supply to the flame arrestor. This can be as simple as a near by vent, though intake noise can be bothersome. I like to duct outside air to the arrestor. This would generally be a large vent in the transom or back of the engine box lid, with a sheet metal or plywood duct that delivers cold, fresh air to the arrestor.

In fact if the duct encloses the arrestor at the carb top, you don't need an arrestor (just a filter), because sparks or back fires will shoot out the duct, not into the engine bay where gas vapors may have collected. This particular trick is currently being used on all new cars as a free way to generate a couple of extra HP.