PTS Flowbench Forum

Another newcomer, looking for info

I had a brain storm about building a flowbench for my own use to get a general idea of how much I am actually gaining by porting.

As Title, I have a laptop & ELM327 USB ECU reader. Is it ok to use a MAF along with a MAP connected to an ecu powered up from the bench and connected to the laptop via the ELM327 to get the airflow?

Would the MAF give the wrong readings (for power calcs) or would it be only useful for general playing?

Also, would the MAP readings give me enough to calculate pressure drop? or would I be better off having a proper vertical manometer?

Diagram of layout attached.

Thanks...

I see where you are going with this but it seams to be a long way around the block. As I see it you are just using the ELM as an A to D converter and the ECU like and eprom. The problem I see is that the ecu is looking for parameterized DATA IE within a specific range, so how will it act when RPM is 0 and MAP is 28” and MAF is +.5VDC????

I get what you are doing but if your electronics and PC skills are at this level then why not find a cheep ADC and build it from scratch to do what you want it to do.

My interpretation of the above is that it would be a convoluted WATER gauge as you still have to take the data and plug it into a spreadsheet or some program.

There are many ADC out here that are VBA friendly and will support what you are doing within the MS Office framework.

I suggest you build the PTS bench for the box and vacuum source then you can experiment with the electronics (I perceive your forte’) at your own pace.

Just a thought.

Rick

PS that is how I started.


And by the way welcome aboard it is nice to see some fresh ideas.

Hi Rick, thanks for the welcome and response

I could have and probably should have elaborated a little more in my OP.

Scantool.net do an ELM327 program that reads and records the ecu data and converts it to something readable in CFM from the MAF and I think KPa (dependent on ECU being used) from the MAP. So basically it's the same as reading the data from the car itself. The reason I was looking to go down this route was for speed - I am very busy at the moment and I was just looking at doing it this way to "get my foot in the door" with a view to building a better bench next year...at some point

The Scantool.net program is available open source which a friend of mine could re-code to enable me to just have the readings important to me. A button could be put in to take a "snapshot" at intervals of my choice and send that data to a spreadsheet. All pretty elementary for a geek apparently

With regard to your comments about the ECU, I don't envisage any problems with it but I could be wrong. I don't see that it could corrupt any readings but it may put a block on a max CFM or block the MAF input if the RPM is 0. I could always rig up a trigger wheel on one of the bench motors with a CKS connected to the ECU . However I remember a few months ago - on a Vauxhall Omega - the MAF was reading 600CFM at 0 rpm and inlet temp was -49*C <- The MAF was completely dead. Could this mean that it doesn't matter???

I guess there's only 1 way to find out. Worst case scenario is I'll have to bin the ecu and associated unusable items and go down a different route as per your post. Not dismissing your input, but curiousity is a crazy *ahem* as I'm sure you know

Thanks again.

J.

I started out flow benching a long long time ago with a leaf blower and a MAF feeding into a digital multimeter.
You will very quickly discover the shortcomings, and then go on to try something different.
Its all great fun and very instructive, but if you wish to build a practical, usable, accurate, and repeatable flow bench it will all be a great waste of time and money.

First problem is that a MAP sensor measures absolute pressure, but the air going into your test piece is at atmospheric pressure which constantly changes with barometric pressure.
The errors will be small, but they will be there, and are something you can do without.
The test pressure reading will never be accurate or repeatable. You definitely need a differential pressure measurement, such as a water manometer or a proper two port differential pressure transducer.
No more difficult to do, and no more expensive, you just need to start off with the right type of transducer.

Most MAFs produce a highly non linear output. The resolution is far higher at the low flow end than at the maximum airflow end.
That is ideal for many things, but the problem with using it for a flow bench is that you need to calibrate the MAF and generate some kind of lookup table for the output to be at all usable.
And you can never be sure how accurate all of that process is going to be.

Rick has the right idea.
Start out with a set of Forum flow bench plans, and by the time you have assembled the bench you will have a much better idea of how to go about measuring the flows and pressures in a simple practical way that is known to work well.

Hi Tony,

Thanks for your input and your backup of Rick's input. I think it is probably best to do it right first time. I'll order the plans soon along with the required items (digiman, OPlates, etc.) Motors I can probably get here in the UK easily enough.

With regard to what you said about the MAP sensor, I was going to have that on the depression side (motor side) of my test piece...I thought that would work OK Maybe I was just being hopeful and my usual cheap@$$ self :p

What do most of you more experienced people use - digital manom or fluid? just curious

jimbo39 wrote:Hi Tony,

With regard to what you said about the MAP sensor, I was going to have that on the depression side (motor side) of my test piece...I thought that would work OK Maybe I was just being hopeful and my usual cheap@$$ self :p

What do most of you more experienced people use - digital manom or fluid? just curious

A very few people here that already have fluid manometers continue to use them.
But the Forum digital manometer is so vastly better, and has so many great features at such an affordable price, I don't think anyone starting out totally from scratch would ever consider going to the trouble of fabricating their own home made water manometers, it just is not worth the effort.

A MAP sensor would certainly work, and you could even use software driven solenoid valves to first measure atmospheric pressure, then measure pressure within the flow bench, and subtract the difference.
That is cumbersome, prone to errors creeping in, slow, and a real nuisance. But its possible.
Nobody ever does it that way when you can just buy a proper low dollar differential pressure transducer and be done...

Another thing to think about.
An absolute pressure transducer needs to operate against full atmospheric pressure, so you are measuring roughly 400 inches above perfect vacuum before you even start measuring test (or orifice) pressures, which are quite low in comparison.
In the Forum flow bench we use a 16 inch range differential transducer, which is going to be far more sensitive and less prone to drift and errors than maybe a 450+ inch absolute range sensor.

As far as flow measurement with an orifice plate goes, mother nature provides us with a perfect square law output of flow versus measured differential pressure drop across the orifice plate.
So its pretty easy to convert measured orifice differential pressure to exact flow in software.
That is the great power of the digital manometer, it reads out directly in CFM on your computer screen.
And you can order orifice plates from Bruce here at the forum to suit whatever measurement range you need.
It solves the problem of calibrating a home made flow bench very neatly.

With fluid manometers you need to use a pocket calculator or spread sheet to do the square law thing with every water manometer reading you take.
Its slow, but it certainly works and is accurate, just a real pain if you are going to be doing a lot of flow bench work.

Digital here. I feel digital is the way to go.

John

This is a great opportunity for a flowbench forum history lesson on the PTS Digital Manometer . . .

Couple year back all we had was PT, FP for digital products, neither was willing to offer support to my PTS Plans so knowing Tony (Electronic Guru) and Rick (Software Guru) I posed the possibility that we could come up with a PTS Product (I'm not a guru just the guy with the idea ) they both said well maybe lets see . . .

So we start in on the project and it progresses along to where we are now, a digital product designed by flowbench people for flowbench people, I kept the price affordable for everyone (one of the deals with the guru guys on what they wanted out of the project). All my parts are priced so most anyone can afford to build a high quality flowbench and not pad someone else's wallet!

I do make a profit on my parts but not a million $$$ profit, you the end user gets quality parts that allow you to build a professional flowbench for alot less $$$'s

So thank Rick and Tony for engineering the PTS Digital Manometer . . . I just put it all together.

Funny thing is we all did this without ever meeting each other in-person, other than Rick and I getting together a few times since we live somewhat close.

I'm all digital

There have been some other members/threads on the MAF setup in the past, they seem to come and go but we never get any good feedback on what they end up with???

Thanks again for the input. Looks like I'll go digiman. I prefer digital anyway

Bruce - I tried ordering the plans online but there's no buy button I created an account in-case it was that but nope, can't purchase.

Bottom of this page:

http://www.flowbenchtech.com/plans.html

My shopping cart does not allow you to make a direct purchase at this time sorry about that