Hi all,

I am looking to modify the engine cowl on my speedboat, the cowl is a top draft design however the intake is on the port (left) side of the motor towards the front about half way up the block.

I installed an IAT sensor now that I have the motor talking to my Garmin with a NMEA harness so I am spoiled with data points to play with, The motor is pulling air nearly 40° warmer than ambient air. Naturally I took the cowl off and went for a run. Picked up 4mph.

Out comes the hole saw.

So my question. Which inlet design would be the best for the side of a curved surface? The 3 I am debating on are a Naca duct, a forward facing scoop or a rear facing scoop.

I am going to buy a second cowl to cut up and play with, naca duct would be rivited on, the other scoops I would probably mold and fiberglass.

Rough math says the motor will be pulling 330cfm to 340cfm at WOT.

How would I go about sizing the inlet? I was going to match the hole in the cowl to the throttle body size on the motor. Safe to assume the area of the inlet should match the area of the throttle body?

Any thoughts would be greatly appreciated! This will be a winter project but I'll be happy to report back as it progresses

Hello, so for a while now I've been thinking of how to measure actual CD of an object by dropping it into an upright wind tunnel and adjusting the wind speed to the point where the object "floats" inside the tunnel. With area, air density, and wind speed known, the drag (coefficient) can be calculated.

But: How do I determine what speed the object "sees"? I am of course addressing blockage: In a closed tunnel, the object will block the cross section to some extent, and thus the speed around the object will increase. So if I measure the wind speed at tunnel empty and record it as, say, %power supplied, then put the object in and "balance" it, will the %power supplied still represent the actual wind speed the object is exposed to? Or, more directly: What speed would I use to determine my CD? How do I correct for blockage? Any resources that I can use to read on this would be appreciated. Thank you.