Okay, I may be WAAAAY late in suggesting this, might have been posted already. But the valve in the cowl induction vacuum line is very similar to the "vacuum delay" check valve used in smog-equipped vacuum advance systems (it is simply spliced into the vacuum advance line). It delays the vacuum signal from reaching the vacuum advance module to reduce oxides of nitrogen emissions, or some such thing. Anyways, they are plentiful and cheap at napa, pep boys, autozone, etc etc. If you pay 10 bucks, you payed too much. Look for one that looks most like the original chevelle unit, as there are countless variations depending on who manufactured the little part. Ford, GM and Chrysler all used em. Oh yeah, if you want LONGER vacuum advance, you can simply install this little device in your vacuum advance line BACKWARDS, and it will delay the vacuum unit from RETARDING. Turn it from a smog part to a performance part.