Measuring air box pressure?

[Corvus]

When balancing the TB you do indeed connect one to each side to detect the inbalance.Then adjust the TBs so that the fluid is the same level in both legs.

In Tapio's usage one leg goes to the airbox and the other left vented to atmosphere. Then pressure differential can be calculated in your preferred units using the SG of the fluid and the displacement of the levels.

I assumed one end of the manometer would be open to atmosphere, but yes, why not just connect each end to each tb. The objective is to equalise after all.

What about fluctuations caused by pulsing? This is quite severe at the inlet ports.

[Corvus]

Initially the use of oil seemed wrong to me as I think too much would cling to the sides and affect the reading. But in our specific example of the you tube video, using each end of the manometer to synchronise a twin cyl engine, we are expecting the levels to be pretty close to start with so I don't suppose that aspect of using oil as a liquid column is much of an issue.

What effect does changing the depth of the "U" make? Will it affect the damping properties with a fluctuating pressure? In other words, even though we are expecting a small difference in height, deliberately making the liquid column high, especially using oil, should make a difference to response. Does that make sense?

[Dai wiskers]

viewtopic.php?t=16632&postdays=0&postor ... r&start=15

Keep reading in one of my posts you will find out how to make a ballbearing manometer

[Corvus]

[quote="Corvus"..............Also, is the reading, in inches or cm or whatever, to be taken from the starting level? In other words half the total difference in height between the two sides' fluid level?
...
[/quote]

No, I think that is wrong. I think it is the total height.

?

[Merecat]

The level of the fluid at rest with the engine off represents atmospheric pressure. Any deviation from that original level + or - in one leg represents the change in pressure.
Best measured in mm so it can be readily converted to pressure units

[Corvus]

The level of the fluid at rest with the engine off represents atmospheric pressure. Any deviation from that original level + or - in one leg represents the change in pressure.
Best measured in mm so it can be readily converted to pressure units

Where I think I was wrong was in suggesting you measure one way, up or down, from the original equalised level.

Now I'm thinking it is the total height difference, but what you're saying seems more consistent with my first impression?

Confused! Heeeelp!

[Corvus]

My reasoning (which may be wrong) is that it is measure of a given pressure to support a column of liquid. That seems to make sense.

It's donkeys years since I used some manometer style carb gauges and anyway, the objective there is to use as a comparator so the actual value is not so important. I wonder if the datum line on those gauges is just as a reference to "zero" the liquid level? Then each measurement up and down from that would be doubled, or the scale would read double?

Wikipedia here I come!

[Tapio]

Update.
Done the test now. In top gear doing 200 kph, I got 11 cm of water. That would be P below ambient pressure in the airbox.

Did a reference test too. I was curious of the ram effect. So brought the bike up to 200 kph, pulled the clutch and killed the engine. Got 5 cm of water above ambient.

This gives, as P is given by: P=q*g*h: 490 Pa of ram effect pressure.

But calculated dynamic pressure at that speed would be, as P = q*(v^2)/2 where:
q = density of air
v = velocity
Calculation gives 1850 Pa.

I’m way off! Why? Water not calibrated? (No, that’s a joke). I think the problem is that the open end of the hose was sitting above the fairing, and that’s a high-pressure area. Thing is, if I tuck it in below the fairing, it will be in a low-pressure area! Where can you find a place with ambient pressure on a moving vehicle?

Why I’m I bothering with this? Well, look at the picture! I’m sure that the K&N cotton gauze filter is better comparing a given surface area with the std filter.
But see how much bigger the surface area is on the std filter! 5 times bigger? 10 times bigger?
I don’t know. All I know, is that I’m not convinced that the K&N filter is the better one of the two.

[Blackal]

If the open end of the manometer is in a high pressure area, you may be getting a venturi effect inside the end of the hose - leading to a higher "apparent" differential pressure.


Al

[Corvus]

Update.
Done the test now. In top gear doing 200 kph, I got 11 cm of water. That would be P below ambient pressure in the airbox.

Did a reference test too. I was curious of the ram effect. So brought the bike up to 200 kph, pulled the clutch and killed the engine. Got 5 cm of water above ambient.

This gives, as P is given by: P=q*g*h: 490 Pa of ram effect pressure.

But calculated dynamic pressure at that speed would be, as P = q*(v^2)/2 where:
q = density of air
v = velocity
Calculation gives 1850 Pa.

I’m way off! Why? Water not calibrated? (No, that’s a joke). I think the problem is that the open end of the hose was sitting above the fairing, and that’s a high-pressure area. Thing is, if I tuck it in below the fairing, it will be in a low-pressure area! Where can you find a place with ambient pressure on a moving vehicle?

Why I’m I bothering with this? Well, look at the picture! I’m sure that the K&N cotton gauze filter is better comparing a given surface area with the std filter.
But see how much bigger the surface area is on the std filter! 5 times bigger? 10 times bigger?
I don’t know. All I know, is that I’m not convinced that the K&N filter is the better one of the two.

Using a dyno would allow you to run on high load (therefore high flow rate) but sample still ambient air too?

If you're trying to compare the two filters, is it really vital that the open end is reading ambient? As long as the test is conducted with the same parameters is that not enough?

Also, would you be better measuring the pressure drop across the filter? ie; the pressure immediately upstream and downstream for each filter?

[Merecat]

So. If the bike gives a Vacuum of 11cm of water @ 200kph
and the ram effect is a pressure of 5cm of water@200kph
than at the sample point the engine is pulling a vacuum of 16cm of water in those conditions. 16cm of water is 15.6mBar

The simplest thing would be to repeat with the other filter and keep all the parameters the same if its just a pure comparison you're after

[Corvus]

So. If the bike gives a Vacuum of 11cm of water @ 200kph
and the ram effect is a pressure of 5cm of water@200kph
than at the sample point the engine is pulling a vacuum of 16cm of water in those conditions. 16cm of water is 15.6mBar

The simplest thing would be to repeat with the other filter and keep all the parameters the same if its just a pure comparison you're after

I think the 11cm includes whatever ram effect there is. The ram test was done separately with the throttle butterflies shut and engine disengaged. So he is literally ramming the air against a dead end. If I understood it correctly?

[Merecat]

So. If the bike gives a Vacuum of 11cm of water @ 200kph
and the ram effect is a pressure of 5cm of water@200kph
than at the sample point the engine is pulling a vacuum of 16cm of water in those conditions. 16cm of water is 15.6mBar

The simplest thing would be to repeat with the other filter and keep all the parameters the same if its just a pure comparison you're after

I think the 11cm includes whatever ram effect there is. The ram test was done separately with the throttle butterflies shut and engine disengaged. So he is literally ramming the air against a dead end. If I understood it correctly?

Indeed. From +5 to -11 is 16

[Corvus]

And what of my suggestion to measure pressure difference across the filter? No good? I thought pressure drop was the time honoured way of determining filter efficiency? Be it air filter, oil filter etc.

Maybe what tapio is trying has a potential flaw in other ways? If he went out one day and did 200 kph. Then went out the next day and did 200kph, who is to say that aero drag will be the same for both tests? More or less drag will mean more or less power to achieve the same speed. Will that equate to higher or lower pressure on the intake side of the engine?

[conkerman]

This. Use your hoover to build a mini flowbench.