Best way to measure airflow of a running engine

[49-1183904562]

[color=#000000]I would think you would need to picture the engine as the Vacuum source and then configure a measuring device on top of it. The trick is you will need to generate some depression at first then work toward zero depression (No airflow restriction) to calibrate your device. Many dyno's use LFE's but they are very expensive. SO if you used one of Bruce

[ThomasVaught]

We do testing quite often with mass air meters. Many, many OEM vehicles (like Ford Trucks) come with large (80mm) mass air meters. There are 4 terminals on the typical mass air meter. The Mass Air Meter is powered up by a 5 volt power source. Two of the terminals go to these terminals +5V and Ground. The two other terminals go to the + and - terminals on a volt meter.

If you generate a "Transfer function" using your Flow bench for different air flow increments you will at some point be able to install the same mass air meter on a vehicle and read air flow while the engine is running.

Tom V.

[wfolarry]

Would it be possible to connect a mass air meter & use it on the flowbench so you would get a direct readout of the mass flow while the bench is giving you cfm?

[Tony]

The big problem with standard vehicle mass flow meters, is that they are all deliberately made very non linear.

A very small change in airflow at around engine idle, produces a fairly large change in output signal voltage. Up near maximum flat out airflow, a fairly large flow change only produces a small additional change in output voltage.

This is ideal for controlling the fuel flow into an engine, but the very curved and non linear signal output, makes these extremely inconvenient for use as a stand alone flow measuring instrument.

[wfolarry]

Thanks. I've often wondered about it. Now I know.

[ThomasVaught]

I have generated transfer functions where I could read anywhere on the mass air meter flow curve with-in 5 cfm. Now 5 cfm is probably not the most accurate for a flow bench measurement device BUT 5 cfm on an automotive engine to determine air flow is more than close enough. I believe the question originally was reading engine air flow.

Tom Vaught

[Tony]

Yes you are quite right Tom.

But measuring some test reference figures on a flow bench, then generating a polynomial with curve fitting software, and then applying the same polynomial with yet more software is probably a bit much for the average person with limited resources.

[ThomasVaught]

Totally Agree Tony.

The deal is most Hobbist type people have limited resources but do have time. Given enough time over a few days you could generate a data sheet in 5 cfm increments for the full range of the meter and put the "polynomial with curve fitting software" requirement for others with less time.

I have personally done this on a home built flow bench so I know it is possible to do.

The hardest part of the deal was getting a realible 5V source to drive the mass air meter. With today's computer equipment it is pretty easy but I used a fully charged battery and a old car computer to generate the required voltage.

Tom V.

[Tony]

The simplest solution to measuring engine airflow is probably an orifice plate and sloping manometer. Exactly the same idea as used in an orifice flow bench, but placed ahead of a carby, or whatever.

If the pressure drop across the measurement orifice is kept low, say no more than four inches of water, you would only lose roughly about 1% of air density going into the engine. That may perhaps be insignificant enough to ignore?

I have never actually tried this, but it may be practical.

[larrycavan]

[color=#000000][quote="1960FL"]I would think you would need to picture the engine as the Vacuum source and then configure a measuring device on top of it. The trick is you will need to generate some depression at first then work toward zero depression (No airflow restriction) to calibrate your device. Many dyno's use LFE's but they are very expensive. SO if you used one of Bruce

[49-1183904562]

[color=#000000]I guess I was not really clear in my thoughts but when you go back and reread your post after you get Quoted, sometimes the light bulb goes on. The wife always reminds me she does not know what I

[bruce]

[color=#000000][quote="1960FL"]Question to Bruce can you do an Averaging Pitot for a 4