I hate to break peoples hearts on this, but the amount of free HP that sealing ducts might translates to isn't measurable. A pretty good estimate for calculting dynamic pressure is 1/2pV^2, and even assuming that 100% of the dynamic pressure is converted to static pressure in the plenum, the pressure is small. If you estaimate that typical air density (p) is around .076 lb/Ft^3, the theoretical maximum static plenum pressure you could get at 150 mph is .3 psi. A small leak at that small a pressure increase doesn't amount to much pressure loss. I used to log air box pressure a couple of years ago. I think the most I saw on my ZX12 was around .4 PSI at 200 mph if I recall. My point isn't that .3 psi doesn't generate HP. It does. But with that much air at that small pressure, a leak doesn't matter much.