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