Road Racing - Interesting underhood pressure results with a cowl hood

So I started off with a string test on the cowl opening, and the string was being sucked into the cowl so air was definitely going into the engine compartment. Then I borrowed a very accurate electronic water column gauge, with the slots sealed off underhood pressure was ~.45" at 65mph, and with the cowl open the underhood pressure was .35-.40". So letting more air in from the cowl area lowered my underhood pressure. :bomb:

I'm curious in these types of measurements as well. I have a few questions though...
with the slots sealed off
What slots are we talking about?

Then I borrowed a very accurate electronic water column gauge
Where is the reading being taken?

Mark.

This will vary depending on where you took your measurements. The theory of the cowl is it 'pulls air into the engine area' after it goes over the hood. Pulling = vacuum, least that makes sense in my head.

If possible, measure MAP readings doing both tests again, and this will tell you if there is a difference in the manifold. Higher reading = more pressure (or in a NA set-up, less vacuum) = more power.

I'm curious in these types of measurements as well. I have a few questions though...

What slots are we talking about?



The slots that open up the rear of the cowl hood to the engine bay.

http://www.trufiber.com/v/vspfiles/photos/TF30020-A49-3-6.jpg


Where is the reading being taken?



Center of the intake manifold on top.

The slots that open up the rear of the cowl hood to the engine bay.

Center of the intake manifold on top.

I'm no aerodynamics expert, but I do know that a decrease in pressure could be the result of a) less air being packed under the hood (this assumes the air in the aera of the reading is somewhat stationary), b) the air velocity in the vacinity of the reading has increased, or c) something else an aerodynamics expert would know that I don't :confused: Opening up the slots may possibly be doing nothing more than just moving the air (or allowing it to move) over the manifold faster. Just my uneducated guess.

So I'm curious... what sort of intake (before the MAF) are you running? Something to take advantage of the cowl slots, or a lid in the stock position?

Mark.

I'm no aerodynamics expert, but I do know that a decrease in pressure could be the result of a) less air being packed under the hood (this assumes the air in the aera of the reading is somewhat stationary), b) the air velocity in the vacinity of the reading has increased, or c) something else an aerodynamics expert would know that I don't :confused: Opening up the slots may possibly be doing nothing more than just moving the air (or allowing it to move) over the manifold faster. Just my uneducated guess.

So I'm curious... what sort of intake (before the MAF) are you running? Something to take advantage of the cowl slots, or a lid in the stock position?

Mark.

This hood let me run a lid in the stock position. I tested the base of the windshield in front of the cowl opening and it only had around ~.5" so it's not as high of a pressure zone as I initially thought.

http://i86.photobucket.com/albums/k106/spddmn24/IMAG0175.jpg