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I am hoping someone on the group will be able to help Johnnes.
Gary
Gary/Johannes,
I think that you are making a very common mistake in reversing what you actually want. Remember that Total Pressure is a constant, and:
Total Pressure = P+1/2 x rho x Vsquared,
where P = static pressure, rho = density and V = speed.
The result is that static pressure increases when airspeed decreases, and vice versa.
So what you want is low airspeed on the forward face of the cooling fins, and high airspeed behind them. This way you have a positive pressure differential which reduces cooling drag and improves the cooling. This is the opposite of what we intuitively feel, which is that high speed before the cooling fins is desirable. We generally reduce the speed by having expansion room in the manifold, so that the air gets a chance to slow down. We can increase speed behind the fins by restricting the airflow through a nozzle, but you do need some room for the air to stabilize before restricting its outlet, and it is difficult to arrange in practice.
EAA published a good explanation of this some time ago, and I posted it on the List under "Engine, Prop, Cowling" in the Attachments section. I just checked and it is still there.
By the way you have made a really good looking manifold. Larry Henney did something similar on his 360, and achieved excellent results. I hope that this helps.
Jerry
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