I asked Terry about the Flowbench he made, here’s what he said – “My flowbench started because I wanted to modify my car’s engine by porting the heads. I don’t know how familiar you are with engines, but “Porting the head” means modify the cylinder head so that more air will flow thru them and into the cylinder. Horsepower is directly proportional to airflow, i.e. 10% more air equals 10% more power. But I knew that just making the ports larger doesn’t mean more for airflow.”
I had used a flowbench in college and knew how they worked and how to calculate airflow from them, so I stopped porting and built this flowbench. A flowbench uses vacuum motors to create a differential pressure across a cylinder head (or whatever you want to measure the flow of) and an orifice (a hole) of know flow. By measuring the pressure drop across the cylinder head as a percentage of the know orifice you can calculate the flow thru the cylinder head. To do this all you need are vacuum motors, which I took out of used vacuum cleaners I got from the thrift shop. Some sheet metal orifices, which I used shells of a washer and dryer I had, because I had taken the motors out to make my planer and disk sanders and hadn’t gotten rid of them yet. Manometers to measure the pressure change. These too are easy to make with wood and plastic tubing. And then a wooden bench to hold it all. I built my first one for $120 and am still using it three years later. Link.