New member, first bench plans, some Qs

[Old School]

Hi all,

been reading (very informative) threads over here for some time, but now it looks I've got bitten by the DIY fb bug...
I have plans to stroke my 350cui to 383cui ('71 Camaro) and perform a good porting job along the way. This could especially pay off, since I've got a pair of World Products Sportsman II heads. These are some of the first aftermarket performance heads from the '80s and seem to respond very well to porting.

My plan is to build a 'simple' flow bench first, then step up to a complete PTS bench, when all works out and/or I get more heads to do.
I've done quite some reading last few days and came across many designs and ideas with related problems and advantages.

Here are some questions I've got:

Thinking of replacing both (analog) manometers with 2 affordable digital manometers, like this one:
Digital Manometer
I understand it's not a very precise (high quality) piece, but so is not a home made manometer/scale/correct calculations diameter & SG/zero-ing etc...

My first Q = will it work the way I think? It will show a pressure drop which can be compared to/calculated with the known numbers of the orifice...?

Second Q = how easy can the PTS bench be adapted to be used this way (and later converted to the original design when I want to step up)?

I'm sure more Q's will follow, but this will give me a good start.
Thx.

[Brucepts]

Welcome to the forum!

I would see no reason that meter would not work you will just have to do the math for CFM which can be done with a spreadsheet/chart.

What I would do is get the 55" one for static pressure and find a lower rated one for CFM without looking I think I once saw some 20" ones? The PTS flowbench is designed to work around a 16" differential pressure on the orifice plates so matching as close to that would be a big start on allowing you to move over the the PTS Digital Manometer and it's features.

They would make an excellent starter flowbench and would adapt to the PTS Flowbench design with no problem.

Actually after seeing your post I might just pick some up and give them a try myself!

[Old School]

Hi Bruce, thx for the welcome and quick replay!

That's the 'power' of internet I guess: even a noob can come up with good idea....
Maybe this thread will be a good start for a 'new' entry level PTS bench...

Based on your knowledge of the design - what parts from your store would you suggest to make this bench the way I'm planning?

[Brucepts]

I just rolled out of bed and checked the forum and your psot was there . . . so yes the power of the internet I guess LOL

First thing I would do if you have not already is get a set of plans, having them in-hand helps you "see" what you are building and how it can be changed to suit your needs. Yes, they are $50 which can be costly but the cost goes to supporting this forum and all it's vast resources and access to some of the best minds in the world! It also allows you access to the forum area where the plans are discussed in detail by those who share thier builds. This gives you ideas on what can be done given each one's $$$'s to spend.

From there it's up to you what you buy from PTS or what you source or build to suit your desire. I'm not one for spending someone else's $$$'s as I would simply tell you to buy everything and make your flowbench once and then get testing

I do understand some like to "tinker" as I am one of those people and that's where this whole forum came from, other "tinker'ers"

[Old School]

That's why I've asked how 'easy' your bench is to first build as I plan, then step up to a full digital design...I think I'll be ordering the plans soon...(BTW - you've now offered the plans for $50 to an overseas buyer... )

Took a look on Ebay - but can't find a 0-20 manometer. I understand what your thinking is - like with an Volt meter - adjust the values to the Voltage you're measuring, but with an (claimed) accuracy of 0.01 - this shouldn't be a problem, would it?

[Tony]

Welcome to the Forum Old School.

Probably the very best first thing you can do is get yourself a set of flow bench plans.
The PTS bench design has slowly evolved over a number of years, and the current plans are the result of a great deal of testing and thinking and many clever ideas.
It will be the best $50 you ever spend.

By the time you have gathered together all the basic parts, manometers, an orifice plate, a bunch of motors, and a way to control them, you might as well assemble it all together based on the PTS design, because the PTS design is a "simple" bench.
It may be simple, but it is a very well proven design and well worth copying.

Those e-bay manometers should work fine, the only disadvantage is the requirement to physically enter and manually convert every pressure reading.
Slow, but it will certainly get you off to a great start.

It would also be planning ahead if you start off from the very beginning using 16 inches design orifice pressure drop as your 100% flow calibration figure.
That is the figure the Forum digital manometer is based on, and it will then make a future upgrade a very smooth transition.

[Old School]

Welcome to the Forum Old School.
It would also be planning ahead if you start off from the very beginning using 16 inches design orifice pressure drop as your 100% flow calibration figure.
That is the figure the Forum digital manometer is based on, and it will then make a future upgrade a very smooth transition.

The only thing I have to do for this, is to buy the 16" Pd orifices - am I right? It won't change or influence the bench design or the choice of manometers, will it?

[Tony]

The only thing I have to do for this, is to buy the 16" Pd orifices - am I right? It won't change or influence the bench design or the choice of manometers, will it?

That is true, it is not really an issue.
But it would be so much nicer if you can just connect up the air lines to the digital manometer and get the exact same figures and readings that you are used to seeing.

[Old School]

So how would a formula look which can calculate the flow using digital manometers?...

Something like:
Let say orifice plate = 200cfm@16"
I measure 14.4" Dp on the manometer
14.4/16x100= 90%
So the actual flow is = 180cfm

Thx all for your inputs so far!

[Tony]

It's not that simple.

Pressure increases square law with flow.
If you double the flow through a hole, the measured pressure goes up four times.
To triple the flow, measured pressure goes up nine times.

If the "hole" flows 200 CFM at 16 inches, and we measure 14.4 inches we have 0.9 times the calibration pressure, as you have already worked out.

We need to take the square root of 0.9 = 0.949 and multiply that by 200 CFM

So a reading of 14.4 inches = 189.7 CFM

Just to make this a bit clearer, our basic orifice calibration point is 16" = 200 CFM
Half that flow would require only a quarter of the pressure.
So 4.0 inches = 100 CFM.
And 1.0 inch = 50 CFM
And 0.25 inches = 25 CFM

The way this is done with a sloping manometer would be the 16 inch rise point would be called 100 % flow on the manometer scale.
A four inch rise would be marked 50% flow, and a one inch rise marked 25% flow.
You would just read direct off the sloping manometer scale (which already has the square root function built in) where at 14.4 inches rise would come close to the 94.9% flow graduation on the manometer scale.

With a digital manometer readout in inches, you re going to have to first work out the percentage pressure, square root that, then in this example multiply the result by 200 CFM.