New Member - have question about flow

[superlen]

Hello,

I'm a new member here and just wanted to introduce myself and thank Bruce for putting all this together.

First a little background. I'm in the final stages of designing a replacement ECU for older Bosch L-Jetronic equipped vehicles, and I'm running my 1977 280z with it. The L-Jetronic system uses a vane type Air Flow Meter(AFM) and they have of course drifted over the years with weakening springs and such. I have collected several to check the output vs air flow and of course need a flow bench. Well NEED is probably not the exact word as I could farm out the data gathering, but I really want one, particularly after seeing some of the awesome designs here.

In the future I will definitely want to be setup to do heads as well, but for now my immediate need is to knock together quickly a system that can check the airflow on these AFMs as well a few stock MAFs. I'm just trying to get a baseline on the older AFMS to see what the average drift is from where they were when they left the factory. I don't mind re-building or making another bench later that will be a nice useful daily driver (sucker in this case), but again just for now, I'm looking for down and dirty... but accurate. For checking calibration on these AFMs I need accuracy, not just repeatability.

I am soliciting advice on what direction I should head on the design. FYI, I have a complete woodworking shop & machine shop so I'm set for tools. For potential vacuum sources I have multiple 1,2 & 3hp dust collectors available, a complete industrial car vac from a commercial car wash that has I believe 4 motors in it as well as a large 15" cast iron blower with 3hp 3phase direct drive motor. My initial thought was to just connect the hose from the car wash vac up to a pitot style bench and use a simple gate to control the flow, but after doing some reading on the orifice design, that may be a better/easier calibrated/more accurate solution.

Thoughts/comments are greatly appreciated.

Thanks,

Len

BTW, I've ordered the plans of course and can't wait to review them once they arrive.

[Hotz]

Hello supelen welcome ...
When you look at the plans Bruce, I believe will direct you to build, how you prepared your workshop, very easy to do.

[Brucepts]

Thanks and Welcome, I've had alot of help from forum members I could not do all this on my own

Build the plenum side of my design and attach your blowers as required.

Would be a dead simple build, John did something like this on his flowbench build and used 2 shop vacs if I recall?

I'm sure he'll be here later on with some input, he's not awake yet. Think he's on MT time.

[jfholm]

CRAP NO! I wasn't awake. It was 4:30 am my time . Bruce is correct as the first bench I built was just the chamber side from the plans. Just plumbed in a couple of shop vacuums, controlled them with Harbor Freight router speed controls and away I went.

[superlen]

Cool.

Thanks for the info already. While I think my Buffalo City Forge with the 3phase will be a cleaner install long term, I think my first pass I'll use the car wash vac. I need to go look but I think there are four vac motors in the top of it.

With the Car wash vac I was just planning on using a bleed valve to control the flow being sucked through my MAF/AFM. If I go with the Forge blower I'll hook a VFD to it which would be nice as then my software can set different flow levels while logging the output of the AFM.

I'll go and snap some pics of what I have.

Lenny

[superlen]

As promised, here are some pics of my possible air sources. The Car Wash Vac only has three motors, not four, and I haven't looked at any of the ratings/numbers on them. For my simple AFM only test I'm sure either of these would be fine. However, if they cast iron blower would make a more suitable long term solution and get me set up to flow heads later, I should use it I think.

The cast iron blower has a 3.25" inlet, roughly 16-18" diameter (i forgot to measure) & has a 2hp motor (forgot to look at RPM on name tag, crossing fingers it's 3450). Any ideas on rough guess of CFM @ 28" with this thing? I'll measure the diameter and check RPM tonight. It will be driven by phase converter.

Thanks for looking.

Len

[Tony]

Hi Len, and welcome to the Forum.

My immediate need is to knock together quickly a system that can check the airflow on these AFMs as well a few stock MAFs.

Now that is something quite different to flowing a cylinder head, because you don't really need to set a test pressure. All you want to know is the actual airflow through the MAF, and the pressure drop across the MAF (which will hopefully be very small) is of no real direct interest.
There will never be a requirement for blow testing, and you have access the wood working facilities to knock something simple together very quickly.

There might also be an advantage of turning the whole thing around, so that the test hole is at one side, and airflow horizontal through the flow bench. That would make fitting the MAF to the test hole a lot more logical.

I am thinking that just the left hand half of a PTS flow bench with a pair of vacuum motors fixed to the bottom with a router speed contol would greatly simplify the whole thing, and do everything required.
That, plus a digital manometer and a selection of orifice plates for calibration would meet all the requirements for MAF testing.

The electrical output of the MAF could also be fed into one of the unused inputs to the data acquisition system provided by the digital manometer, which opens up a lot of interesting possibilities....

[superlen]

Tony,

What you described is exactly what my plan is. I keep looking my big blower because at some point I will want to flow a head but my immediate need is just to get accurate Volts Out/CFM through the AFM/MAF so the vac motors will probably win out. I've got a full woodshop so the cabinet is a no brainer & I will design it to mount the AFM/MAF sideways. The MAF doesn't care but the AFM is spring loaded & has some weight to the flap. Vertical vs Horizontal may make a difference. I'll check when I get it operational.

To play with this weekend I have two Dwyer 475 mark II DMs that a friend gave me. They are 200" so they may not give me enough resolution at the bottom end. Long term, I'll change the code in my ECU & use it for the final DM, but currently it has a 100kpa gauge sensor so that's no help at all now. LOL. I ordered some 10kpa's today and I have 16bit ADC so that will give me enough resolution. I'll just attach them to a couple of the other analog channels for data acq and logging.

This setup will allow me to measure simultaneously the AFM & CFM realtime and show them on the GUI.

This forum has been great to allow me to quickly wrap my head around the physics. It has sucked from the aspect of now I want to build a kick ass flow bench and thus added another project to my list.

One thing I'm still a little unsure of is chamber size. If I understand it right, I need a large enough chamber so that the orifice's CD isn't sensitive. (CD going up if orifice diameter is close to chamber diameter such as one in a piece of 4" pvc). My gut instinct is to build a chamber around 16deep x 16 tall x however long is convenient and splat an orifice in the center. AFM/MAF on left, Vac on right,measure the DP. Since the pressure needed to flow through the MAF is small, I may need a fairly small orifice anyway to get an appreciable DP.

I'll fab an orifice this weekend. I've got some 1/4" AL stock and some 1/8"AL stock, lathes and mills, ect. Would one thickness be any better than the other? I'm leaning towards the 1/8, but I can chamfer the internal radius as needed on some 1/4".

Comments are welcomed as I'm a relative neophyte on the physics going on here.

Thanks again,

Lenny

[jfholm]

Here is what I threw together in a couple of week ends of spare time. I just needed something quick and I did not have a lot of money at the time and want to just use what I had. I bought Bruce's plans and just did the chamber side like Tony and Bruce have mentioned. Works great! With two shop vacuums it will pull 12" H2O test pressure through a good Small Block Chevy head.

It is not a super clean job but it works great!

John

[Tony]

To play with this weekend I have two Dwyer 475 mark II DMs that a friend gave me. They are 200" so they may not give me enough resolution at the bottom end. Long term, I'll change the code in my ECU & use it for the final DM, but currently it has a 100kpa gauge sensor so that's no help at all now. LOL. I ordered some 10kpa's today and I have 16bit ADC so that will give me enough resolution. I'll just attach them to a couple of the other analog channels for data acq and logging.

This setup will allow me to measure simultaneously the AFM & CFM realtime and show them on the GUI.
Lenny

I would still prefer the PTS digital manometer.
The pressure transducer that measures the flow orifice differential pressure is 16 inces full scale, and the digital manometer uses all of that range for highest possible resolution and accuracy.
The software that comes with the DM also displays CFM directly on screen.
Its really the perfect off the shelf solution, and as you wish to get this going fairly quickly, would be the most straightforward and least troublesome way to get it all up and running.