Siting Cold Air Intakes on a SOARER

Sunday November 18 2001

I used the manometer today to measure pressure areas at different speeds at three bumber locations.

I used a small red funnel on end of the hose and with just the tube taped to various locations. As expected the funnel didn't make a lot of difference since we are measuring static pressure (or trying too). The funnel also made the readings bounce around a bit (turbulence?).  I didn't like reading the manometer with the funnel - just the tube gave nice smooth readings.

The manometer with funnel attached:

Here are some pics of the pickup locations;

1. Funnel below licence plate

2.Replacing funnel with just the tube taped there.

3. Taping the tube near headlight

4. Funnel to the side below the headlight (where my stormwater inlet was sited, or where the TT intercooler inlet is - next to the bottom lights).

The tube was routed through to the car

Manometer in passenger compartment. So at 100 km/hr the average pressure available is about 4.5 cm of water. The SS inductions unit and the stormwater inlet easily got this. Doesn't really matter where you get the air from.

Pressure is force divided by area. Sticking your hand out the window at 100 km/hr you feel a force on your hand, part of it is drag and the other is this small pressure times the area of your hand.

The BFI gets about 3 cm of water at the moment - it leaks everywhere - but it delivers huge volumes of air and doesn't impede flow at wide open throttle - that's why it outperforms piped inlets to the standard airbox hole.

So I need to seal the BFI to raise the pressure - then increase the intake area to raise the volume.

Under full throttle nothing touches a BFI.

And the pressure available at 100 km/hr is the same as the pressure at the bottom of this glass of blackcurrent juice - not much is it?

The best cold air intake will deliver a pressure (closed throttle) of say 2 inches (5cm) at 100 km/hr.

This is equivalent to a Supercharger or turbo cranked up to 0.07 psi - wooHooo!

It's not much but combined with volume and coolness it does make a difference.

I reckon taking the air from below the licence plate is as good as any. From Bernoulli's equation a funnel will have no affect on the stagnation pressure as it relates to airflow speed. The funnel may however serve to create a full stagnation point, as opposed to a straight pipe on the front of a curved car nose where the flow would not be completely stopped.

The pressure recorded by tube and funnel didn't vary that much. The manometer is measuring equal pressure all along the tube. No air is moving in the tube at all. It is still(not moving) air, at a higher pressure.

The funnel serves to collect a still reservoir volume of air, but the air spills out causing tubulence - much like a toy parachute with no vents - it rocks side to side spilling air. Since no air is passing through the funnel, the air is not compressed - it is nothing like a jet engine. This is purely a measure of the pressure available at the front of the Soarer.

I doubt we will get any Venturi effect with a cold air intake. WHAT IS VENTURI (Bernoulli Principal) EFFECT?

In physics, the concept that as the speed of a moving fluid (liquid or gas) increases, the pressure within that fluid decreases.

Originally formulated in 1738 by the Swiss mathematician and physicist Daniel Bernoulli, this principle states that the total energy in a steadily flowing fluid system is a constant along the flow path. An increase in the fluid's speed must therefore be matched by a decrease in its pressure. In other words, in regard to temperature, as pressure decreases gas expands and heat is dissipated (temperature drops) because of lower pressure (less density) at greater volume dispersing the kinetic energy.

The above is why air leaving a nozzle or discharge port of an air tool often feels cold. Condensate may also be seen because of a lower dew point.

I was measuing the pressure build up in front of the car while it was moving and it was not total pressure, just the difference over atmospheric pressure.

I was using "static" to describe the increased pressure in a sealed container (no air movement). The sealed container I am interested in is the one just before the airfilter. I measure it by plumbing a tube into it, the pressure equalises in the tube and I can read the pressure build up just before the air filter.

Maximum you can get is 5cm of water pressure or 2 inches at 100 km/hr. This is a good test to see if you are getting maximum pressure in the airbox - has to be done with throttle closed. Not related to volume. The other test is to measure maximum vacuum in cm in water during wide open throttle. This is the killer test - this is related to volume. If you can't provide enough volume of air you get a vacuum.

This is where the SS inductions and Stormwater pipe (both giving excellent high pressure (max available) during closed thottle at 100 km/hr) fell over. Neither of them could provide enough volume at wide open throttle - big nasty vacuums develop in both of them (-4cm of water).

The simple elephant snorkel didn't develop hardley any positive pressure as it stopped under the headlight - but it delivered plenty of volume (-1.5 cm of water). A big improvement over the piped intakes to the standard hole.

But I wanted more, I wanted at least 0 cm of water during wide open throttle so the elephant snorkel was abandoned.

The BFI was astounding in this regard. It went better than zero - it was developing +ve pressure even under wide open throttle. I didn't believe it at first - had to recheck everything and do test again and again. Always the same. Under wide open throttle the pressure was +1.0 to +1.5 cm of water. As the car accelerated more air went into the scoop than was needed.

I then tested the vacuum behind the filter and it had dropped markedly too.

I plan to rig up the funnel and manometer on he dyno and see what sort of pressures can be generated with the little dyno fan (and then compare to the 100 km/hr pressure).

The moral of the story is that you can develop pressure in airbox taking air from anywhere.

The real test is the pressure before the filter during wide open throttle.

Note: When you make your own manometer, if the liquid in the tube connected to the airbox goes up (vacuum) to, say, 2cm of water, the liquid in the other tube will go down by the same amount.

The liquid in both tubes should be level before testing. Anyway, up by 2 on one side, down by 2 on other side, total vacuum is 4cm of water - the difference between the two tubes is the important bit.

I eagerly await anyones results - surely I'm not the only one testing intakes like this...

another note: I am talking about a U-tube manometer - measures pressure and vacuum, is lighter, easier to make, doesn't spill, more accurate etc. (a single tube manometer is like putting one tube into a coke bottle, it can measure vaccum only, you measure how far up the tube the water travels - but the level in coke bottle goes down a bit as well - so you have to measure from inside the bottle - what a pain.)

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