LFE's

[cboggs]

I understand the FlowData flow bench uses an LFE
or laminar flow element.

I know where to buy these, .. are they good to build a home bench
with? If so, how would the bench be built?

Would this be good if you want a really accurate bench?

I don't understand how they work, .. how DO they work??????

Curtis

[Mouse]

Curtis,

LFEs are very accurate, but very delicate. They are basicly a stack of straws that create a pressure differential, just like an orifice. If something gets in there, it will wreck the element or throw it off calibration. They require calibration and may require recalibration at times. They must not be allowed to get dirty. You MUST also account for temperature, humidity and Baro in your calculations, but if you get all that correct, the flow formula is linear.

My opinion... while they are an excellent high precission flow element, there are better options for the home builder.

John

[86rocco]

You might find some useful info here

[Thomas Vaught]

I use an 8 inch diameter LFE to calibrate orifice plate benches I
have built but I totally agree that the elements must be kept
clean with great filtering, the sintered bronze elements at the
tap locations can be clogged if you have trash in your manometer or fluids, and you must make the corrections Mouse mentioned.

Ford Motor Company can buy any bench they want and used for
years LFEs for carb flow lab work.

Today the Engine Engineering people use a Turbine wheel type
suction device to pull through Precision Nozzles for flow stand work
on intakes and cylinder heads.

At the Scientific Research building where I work we have a multi-
million dollor venturi element type bench for our work.

Here is the link:



Once you are in the Technical Area, click on PRODUCTS, then
AUTOMOTIVE, then Intake and exhaust flow testing

There are 6 ranges. Each venturi is in the properly sized pipe
and the bench is completely computer controlled with very good
data acquisition and report capability.

I will try and post a link to a picture of the bench.

You could make a similar bench that mounts on one vertical wall
but with pitot, orifice, or venturi measurement orifices.

Tom V.

[aleaskp2]

I'm a total newbie at this so please forgive my ignorance. Per Mouses post regarding temperature, humidity and Barometric pressure. Do these corrections not have to be made for the other types of benches as well (Venturi, orifice etc.)? Aside from the cost of the LFE (I was quoted $2037.00 for a 6" unit by Meriam) and the cleanliness issues, why would the LFE system be a less than ideal setup?
I realize that the orifice style bench seems to be the most popular, but it also seems to create a large amount of problems for the builders and users.

[larrycavan]

Here is link to what superflow has to say about temperature, humidity and it's affect on their orifice type benches.



Larry

[aleaskp2]

Thanks for the link to the SuperFlow FAQ pages. I must have missed them when I was looking at their benches a while back. While reading through the literature that they sent me, I noticed what appears to be some contradictions regarding their claim that their benches are unaffected by atmospheric conditions.
It's the little things, like the fact that the SF600 has a thermometer measuring the airflow temp on the bench. If temp has no effect then why spend the money to include it?
The FlowCom unit that is optional on most of their benches and standard on the SF1020 (Which uses no manometers at all)"...is an accurate, easy to use digital airflow measurement system that takes pressure and temprature measurements on the flow bench and shows calculated and corrected flow in real time..." Again, why is this necessary if atmospheric conditions have no effect on the readings?
I understand that the ratio between the pressures across the orifice and the valve are unaffected by atmospheric conditions, but the airflow that is calculated from the pressure drop would be. The air flow of the test piece is expressed in CFMs, rather than as a ratio such as 12% increase or 19% increase (or decrease).
I also took a look at the Merriam Instruments website. I see that the manometers are affected not only by atmospheric conditions but by variations in gravity due to differences in lattitude as well. SuperFlow never mentions any of these things with regards to their products, but they are quite happy to trash an LFE bench.
Perhaps a talk with someone from FlowData is in order.
[U]

[Mouse]

We do make many assumptions when flow testing. Yes, you need to get a copy of the US Geological Survey map of your local gravities to compenstae your manometers. Mountainous areas are particularily effected by gravity variations.

[larrycavan]

To me, the whole concept of measuring airflow can be taken to such and extreme that it becomes overkill for engine performance improvement applications. [common porting uses]

To begin with, air temperatures and qualities are perpetual variables. Granted, the finer you can calibrate any mixture delivery system to the ideal for a given engine, under a given load to maximize efficiency, the better off you are.

There are concepts that I had dreamed up regarding the intake tract of 4 cycle internal combustion engines that would include, variable port volumes controlled via vacuum or celenoids. When used in combination with an elaborate fuel injection & ignition system with multiple injectors and variable cam timing, it would be possible to achieve the ever elusive ultimate A/F mixture, velocity & volume to match load and rpm. We'll leave compression as a static value for the moment although cam timing is cylinder pressure related.

Constant Velocity carburetors are the simplist form of a variable, engine demand A/F delivery system that comes to mind. They do however only control the mixture delivery at the fixed sized port entrance. What if the entire port roof or floor or both could be varied to match the demand of the engine for any and all rpm and loads?

We have all the intracacies of variable cam timing and fuel injection / ignition systems that are computer controlled to deliver the optimum. What's left in this puzzle is the variable port.

What we're all shooting for in our intake delivery improvement methods is to increase BMEP through transitionally sized, non flexing ports and that has all the natural inheritance of being RPM limited in effectiveness.

To me, the variable port would be the system where the extremely fine grained airflow measurments would begin to be practical in application and worth the effort to measure.

Just my thoughts at the moment...and ALWAYS subject to change and debate...

Larry