That diaphram CLOSES the secondary intake runners. If the diaphram were to be left with no vacuum lines running to it, the intake runners would stay OPEN all the time. There is a little black vacuum box under the intake manifold that closes the intake runners as soon as you turn the key on. At a certain RPM your computer shuts the power off to that vaccum box and your intake runners open up. You can acctually take the top of the intake manifold apart and remove the whole runner setup for a strait through manifold. I havent done it to my h22 but someone i know with a prelude did it(he had a fully built h22a) and said it made a big diffrence. He did it when they didnt make an aftermarket intake manifold and then when skunk2 came out with one he bought it. After installing it he said there wasnt much of a diffrence in the two. So im guessing doing that would cause it to act more like a race manifold.