I know some people have big budgets for their cars, and mine is pretty small, but for me its about the challenge of doing something and following my ideas, rather than having people telling me I cant do what I want to. So when I decided that I wanted to port a cylinder head for my polo, I decided that I needed to do some research instead of just attacking a cylinder head with a dremel and hoping for the best. So I ended up making a flowbench for £15 (not including the wet and dry vac I already had).
so the idea of a flowbench is to measure the the volume of air that can flow though a port at variable valve openings at a given pressure drop. Now I know it can only do that at a steady flow rather that trying to replicate the dynamics of valve opening and closing etc that happen in the real world.
so I fell across this web page
www.dwyer-inst.com/Products/AirVelocityIntroduction.cfm
and then I began to play. now I based my flowbench on 40mm plumbing fittings as they are cheap and easy to get hold of and larger than the ports I was wanting to test.
so this is my version of two nozzles needed to make a pitot tube (which measures the air velocity and because you know the diameter of the tube, you can then calculate the volume of air movement)
and here it is in a tube (shown with an early very sensitive manometer that I used but then decided that I didnt need the accuracy).
I need two manometer, a small one to measure 12" of water pressure (to measure the air velocity with the pitot tube) and a larger 36" one to measure the pressure drop between the port and atmospheric pressure. I made mine from airline for fishtanks, a peice of wood and electrical cable clips
then I needed to make a valve to adjust the pressure drop, this is like a bypass that lets the vacuum suck in unrestricted air and is opened or closed to adjust the pressure on the largeere manometer. I used 25 inches of water, which is just under 1 psi.
and then there is the plate that the pumbing tubing fits to the head. yes its mdf and the centre from a roll of cellotape, but since its bore is the same as a polo engine, its all good (and cheap).
The valve adjuster is a peice of plywood with a M6 threaded metal bush with a nylon tube on the outside with a slit down the side, so it grips the valve. as the thread pitch is 1mm each turn of the knob opens the valve 1mm.
and here is the final set up show testing a head. the two manometers are in the background and plasticine is used to smooth the air flowing into the port. bolted on top of the head is a plywood plate with a threaded adjuster.
I also made a tiny pitot tube, so I could see the differences in velocity arround the port and give an indication about what I needed to do. its a 1/16" o/d tube inside a 1/8" o/d tube.
of course its not the worlds most accurate peice of equipment, but its fit for purpose. One thing that surpised me with flow testing is the noise, as it was deafening as I needed to wear ear defenders on the standard head. of course noise is vibration which is turbulance, so and the flow gets better the noise goes as the turbulance does.
the inlet valves on the head Ive done are 32mm diameter, and that is jusy about the limit of the vacuum cleaner I used to give a pressure drop of 25 inches of water.
also if you want to compare two flow rates, you should take into account barometric pressure, humidity and temperature, as these will change between one one and the next. my alternative is to do back to back testing on a standard port and then use that for comparison as it means you don't have to worry about complex maths.
so the idea of a flowbench is to measure the the volume of air that can flow though a port at variable valve openings at a given pressure drop. Now I know it can only do that at a steady flow rather that trying to replicate the dynamics of valve opening and closing etc that happen in the real world.
so I fell across this web page
www.dwyer-inst.com/Products/AirVelocityIntroduction.cfm
and then I began to play. now I based my flowbench on 40mm plumbing fittings as they are cheap and easy to get hold of and larger than the ports I was wanting to test.
so this is my version of two nozzles needed to make a pitot tube (which measures the air velocity and because you know the diameter of the tube, you can then calculate the volume of air movement)
and here it is in a tube (shown with an early very sensitive manometer that I used but then decided that I didnt need the accuracy).
I need two manometer, a small one to measure 12" of water pressure (to measure the air velocity with the pitot tube) and a larger 36" one to measure the pressure drop between the port and atmospheric pressure. I made mine from airline for fishtanks, a peice of wood and electrical cable clips
then I needed to make a valve to adjust the pressure drop, this is like a bypass that lets the vacuum suck in unrestricted air and is opened or closed to adjust the pressure on the largeere manometer. I used 25 inches of water, which is just under 1 psi.
and then there is the plate that the pumbing tubing fits to the head. yes its mdf and the centre from a roll of cellotape, but since its bore is the same as a polo engine, its all good (and cheap).
The valve adjuster is a peice of plywood with a M6 threaded metal bush with a nylon tube on the outside with a slit down the side, so it grips the valve. as the thread pitch is 1mm each turn of the knob opens the valve 1mm.
and here is the final set up show testing a head. the two manometers are in the background and plasticine is used to smooth the air flowing into the port. bolted on top of the head is a plywood plate with a threaded adjuster.
I also made a tiny pitot tube, so I could see the differences in velocity arround the port and give an indication about what I needed to do. its a 1/16" o/d tube inside a 1/8" o/d tube.
of course its not the worlds most accurate peice of equipment, but its fit for purpose. One thing that surpised me with flow testing is the noise, as it was deafening as I needed to wear ear defenders on the standard head. of course noise is vibration which is turbulance, so and the flow gets better the noise goes as the turbulance does.
the inlet valves on the head Ive done are 32mm diameter, and that is jusy about the limit of the vacuum cleaner I used to give a pressure drop of 25 inches of water.
also if you want to compare two flow rates, you should take into account barometric pressure, humidity and temperature, as these will change between one one and the next. my alternative is to do back to back testing on a standard port and then use that for comparison as it means you don't have to worry about complex maths.
