How many CFM of air will flow through a duct measuring 1"x9" at 60mph?

60mph =63360 inches per minute.
A duct 1"x9" is 9 sq. in.
Cubic foot of air is 12x12x12 or 1728 Cubic inches of air.
1728cu in / 9 sq in = 192.
So one cu foot of air is 192"x1"x9".
192x1x9=1728 cu in or 1 cu foot.
63360 inches per minute / 192 inches = 330 CFM.

Now did I figure this out correctly?

So if my duct opening is 9 sq in and my SMIC is 204 sq in (12"x17").
Then I'm passing 1.6 cubic feet of air through each sq in of SMIC per minute at 60mph barring any obstructions or .026 cubic feet of air per second or 44 cu in of air through each sq in of SMIC surface area. So the SMIC has 44 inches of air going thru it each second barring any obstruction.
I’m traveling 1056 inches per second at 60 mph and 44 inches per second of air is going through the SMIC.
That tells me my small duct opening (1”x9”) is a bottleneck.

I guess that is why FMICs are better for cooling the IC.

Am I right on these calculations?

Ken

 

So if I'm getting 1.6 cu ft of air going through each sq in and my 1630CFM electric fan is pulling 14 cfm per sq in. The fan is pulling way more air through than the duct is at 60 mph. 12" fan(6x6x3.14) = 113 sq in surface area. 1630/113=14cf per sq in.

That explains why the fan sucks hot air from the engine side of the intercooler that is not covered by the electric fan into my duct area and through the IC where the fan is. I guess I should get a switch to turn the fan off at cruising speeds or at least get a switch that regulates the speed of the fan. No sense sucking hot air from the engine thru the IC.

I'm experimenting with some paper that covers the back of the IC that is not exposed to the fan. When the fan is on it just sucks the paper to the IC and prevents hot engine air from being sucked into the duct and going through the IC where the IC fan is.

Oh well, I guess I should not have gotten such a powerful fan. It sure will help heat soak on the dyno or in stop and go traffic.

 

Thats why I made my duct opening 24 square inches. The duct opening should be roughly 20% of the core. My core is I think 11x12 = 132" (roughtly M2 med) and at 20% my duct should be 26.4". Well, I think mine ended up being abount 24" but still, thats close enough.

The reason it only has to be 20% is because a large % of your core is metal and it doesnt flow air.

BTW - You might want to double check that duct opening, I was thinking even the stockers opening was bigger than that.

STEPHEN

 

SCC saw 158F intake temps, 12 psi, 90F day, with m2 med at track, due to that duct restriction.

I had similar thought of some 'flapping louvers' too ... kinda crude. But the 10 sq in duct throat is still a big problem ... will throttle down a 12" fan to 1/2 capacity or less.

For short power bursts, just need to precool the core mass, and small duct inlet is ok. A shroud behind the IC, mabe 1/2" off IC face, would prevent recirc and core preheating. But for big track events, need to open the throat as close to 30-40% of core size as possible.

Ken ... see my post on hp calculator with h20 injection? mabe pg 2-3 now.

 

Sorry, I missed that one. Did a search and found it, THANX.

I'm thinking about using my spare Aquamist pump and run another line from my water fuel cell and use my extra injectors to spray water in the duct to the SMIC. Have a switch and when on it would spray a mist of about 300cc a minute of water on the front of the SMIC. That should help cool the sucker down.

Ken