Hello all, first post. Fluctuating manometer q

[ThePinnacle]

Glad to be a part of this forum. Lots of great information here.

I got started on this flowbench thing after reading the article on Gofastnews.com about the super cheap flowbench. After I built it I found that it was just about impossible to get any meaningful measurement out of it.
So from there I did more reading and I added an orifice plate to my setup. I also happened upon some legit Dwyer manometers that my machinist happened to have that he was no longer using.

Right now I just have kind of a cobbled together system just to get an idea of how it all works and see if I can get some valid measurements. It is powered by two 6.5 horsepower shop vacs.

My problem right now is that taking manometer readings is extremely difficult due to the fluctuations. My latest idea is to simply take a picture of the manometers while running a test to get a freeze frame of both of them no matter where they are moving. I'm not sure that's going to work.
I'd really like to get rid of these fluctuations and as far as I've read there seem to be no simple answers. I have added needle valves in line with the manometers to try and dampen them but this still doesn't work very well. I bought another valve to add to the high pressure side of the orifice plate manometer to see if that helps. We will see.

I made a little video of it here


A few comments on the video, this is in my shed which happens to be against the fence with my neighbors yard. My neighbors apparently think a suburban house should have chickens and roosters so that's what you hear in the background
Since the video I added a second 6.5 hp shop vac that i bought for 25 bucks on craigslist. This didn't really improve the amount of vacuum as much as I thought it would. Maybe a couple of inches at full tilt. It also didn't affect the fluctuating manometer readings.

The heads I'm working on are 3.8 V6 turbo Buick heads that flow a terrible 155-ish cfm on the intake stock. Most aftermarket head porters get only a few hairs past 200 cfm with them.

Right now the orifice I use is not a precision machined piece. I used a turret punch to create a 1.25" hole. I then flowed the stock head and played around with the c.d. in the equation of the orifice flow to match the flow seen by most of the documented flow tests of these heads. I now use this number to do the math on my other readings to see what cfm I am at. I'm not too concerned with absolute accuracy. I really would just like a repeatable and accurate (in the relative sense) method of comparing port changes.

Any advice on the manometer problems or anything else would be appreciated. I'll be building something more permanent when I work out the kinks on this.

Thanks,

Pablo

[bruce]

Welcome to the forum!

Nice video and explanation of your bench. You'll notice that a few members from here have already discussed the Gofastnews.com bench design in a few posts both here on this forum and over on GFN and offered their ideas of the design. ???

There probably is no easy way of saying this but . . . dump the orifice in a pipe design

You will chase your tail for sometime and then finally realise it won't give repeatable numbers. There is a good thread here on the forum about orifice in a pipe. Now that you have a pretty good understanding on a simple bench (don't think the orifice in a pipe design is a simple bench) take sometime and build an orifice style bench. It will take up less space than your pipe laying all around and work much better. Since you have the vacuums all you need is the plenum area. Go over to the orifice area and do some reading, Jholm a member here has some pics of his build over in that area and I'm sure others will be along to offer some advice.

[106-1194218389]

Pablo,
Let me just say I would take Bruce's advice. I actually worked on this type of Flow device for a long time trying to make it work. What we found is you need a settling chamber. Your orifice diameter needs to be less than 40 or 50
% of the tube ID. Also we found you need at least 6" ID PVC pipe. Then you also need honey comb air flow straightner way before and after your orifice plate. The one thing I did also notice was that your pressure taps seem to be at least two or three inches from the orifice plate if your orifice plate is indeed in the middle of the two pressure taps. Your pressure taps need to be within 1/2" for the orifice plate to get in as much dead air space as you can be. That is where I think your fluctuation is coming from. But even after you have done all of this it still will not be as good as an orifice bench. I spent all of my time just chasing after PVC pipe and parts to make it work. The size you need is hard to find. I threw together my orifice bench just to see if it would work better. IT DOES! You would not believe how repeatable this is. I used my 2 shop vacs at first and if you notice in the pictures, I designed it to reuse the head adaptor and stuff I had used with my FlowQuik and orifice in a tube bench. This thing is ugly, but accurate and repeatable. I now spend my time porting and not trying to get my bench to be accurate and repeatable. go here to see it and if you need more pictures I will post them. Do yourself a favor and buy Bruce's plans and build one of these. You will then have a "real" bench. I will guarntee it will be as cheap if you count all the running around and PVC I bought. Actually much cheaper.

John

[ThePinnacle]

Thanks for the replies guys.

Bruce's bench definitely seems like a good investment, but what can I say, I am stubborn. For better or for worse (mostly worse) I like to figure out things for myself. I'll probably break down and buy the plans soon anyway.

I went ahead and moved the pressure taps to right up against the orifice plate, I also added another needle valve to the high pressure side of the orifice plate to try and dampen the readings.

This really didn't do anything for my pressure fluctuations. I will no doubt need to build a settling chamber to get this to work right.
In the meantime I tried taking pictures of the manometers. I take 5-7 pics of them and then average the readings. This actually seems to work somewhat ok. Every average I have done is pretty close despite some of the individual readings being way out in left field.
So I started flowing a stock head and wanted to see what individual changes did. I've already learned some interesting things. Mainly that you don't need to do a whole lot to increase flow significantly from stock, just opening the valve throat and blending it out gained me "26 cfm" at .4 lift. I then ground away from the biased side of the valve guide and shaped it like a 9. That netted me another 10 cfm at .4. This port already flows more than another port I did where I just started hogging things out like crazy. I've hardly removed any metal on this one.

Anyway, what do you think about using two 5 gallon drums stuck together as a settling chamber? I'm talking about the kind of drums you buy your race fuel in. I have a few of those laying around and was thinking about cutting out the bottom of one and then placing the orifice in the bottom of the other, sticking them together, and then putting an inlet and an outlet on the thing. Think that may be too small? Does it matter where the air enters? I was thinking that it might not be a good idea to have the inlet pointed directly at the orifice but rather curved toward the wall or something so the orifice doesn't see any "ram" effect from the air coming out of the pipe. Hopefully that makes sense.

Thanks again,
Pablo

[Tony]

Hello Pablo, welcome to the Forum.

As has already been said, orifice in a pipe is a hopeless method of accurate flow measurement, unless the orifice is made very small, and the pipe diameter made very large. Your idea of using a couple of fuel drums is a good one for an initial experimental prototype.

It may fix the problem or it may not, but it is a definite step in the right direction.

Another possibility is that your vacuum cleaners are not producing a nice stable vacuum and nice stable flow. That long convoluted hose may be strangling the blower, and producing all sorts of flow instability problems.

By the time you have built a large settling chamber, and removed the blower from one of your vacuum cleaners, and fitted it to a suitably large free flowing blower box, you will have something pretty similar to what many people here are running successfully.

Or you can just get a copy of the excellent Forum Plans, and get it exactly right the first time without all the trial and error messing around.

Pablo, we have all gone through the stage you are at right now, and know exactly how you feel !!!

By all means experiment, but the Forum plans are the result of a lot of knowledge and practical experience and well worth checking out.

[bruce]