Yeah thanks mate Iam in the middle of designing one That's similar but got all these things and a round bottom so air can flow easier. I was needing basic dimensions to work around I haven't got a blaster in middle of purchasing one just buying and making things to all go one once I get it. I will post my designs and finish product once complete. The lid that goes over the box how much of a gap does it leave at each sides when on its not flush to the side with a tight seal?
Let me point out he CFM box flows plenty for a 32mm or smaller carb on a 200cc 35hp motor. It seals well, but could be better in the flow and tune department for larger motors.
I am using my gasketed seat bottom as the lid, and the only gap is at the front. The gap needs to be about the same area and needs not be any larger than the carb venturi. The carb is dealing with high velocity pulsing air. The same diameter opening will flow much more constant smooth flow air. So for a 39mm carb area is about 1200mm2. A 6mm (1/4") lid opening 200mm (8") long would more than do the trick, or about a 35mm square opening or any combination getting about 1200mm2.
Where I live is very wet and muddy. Very hard to keep that stuff out of the intake so a good seal and filter is important.
The goal with any intake ducting is generally a gentle trumpet shape up from the smallest obstruction, which should be the carb venturi. Some work I have been doing with piston ported motorized bicycles show a powerful effect from straight duct and a sharp taper at just the right distance from the intake port window. Piston port engines are more affected by intake tract tuning. For reed valved engines distance to the reed is most important and should be about 7"-8" for 8000-9000 rpm.
Don't reinvent the wheel if you don't have to. I buy a lot of stuff and try it out just to know. Some amazes me, some disappoints. I can give you measurements later, but have some photos of the stock airbox and the mods I made to mine for the larger carb.
I've also worked with port dividers both before and after the carb and into the reeds. There are some impressive part throttle gains to be had and these dividers are very effective for maintaining constant port area at the reeds.
It is a big field with lots of room for experimentation and gain. I can almost guarantee you that the first airbox design you build will not be the best. Fab something up cheap and simple to test designs before you build a beauty.
Steve