Question regarding Vented or not vented gas cap, plz advise
 

Hey all. When I got my 79 911 sc and took it to emissions, the lady there suggested that I go get a non-vented gas cap. I went to the parts store and did that. But now I am curious. The one that was on it before had a two smaoo, 1/8 holes drilled into it.

What would be the reason, and should i put that one back on or what. Let me know please.

I'm not familiar with 79's, but from your post it sounds like that year was supposed to have a non-vented cap. I got the impression that your car passed anyway, but the tech suggested you change caps, is that correct? If your car passed, and runs fine regardless of which cap you have, then it becomes a matter of choice, though the vented cap will release some fumes in to the air. Some newer cars will not run properly with vented caps, but it doesn't sound like yours. If you were in Cal., your car would fail automatically if the improper cap was installed. I know this isn't a difinitive answer, but it should get the ball rolling.

Larry