Ok so the other day my fuel line got replaced (a different incident all together) and when i was at the track wednesday my car was a little slow. The next day i filled up with gas and found that my gas cap was just resting in the hole. They never screwed the cap back in after they were finished. So what im asking is how much did that hurt my fuel pressure and my 1/4 mile time? Thanks in advance

 

You could throw the gas cap away, wouldn't make a difference performance wise. If it was left off long enough, the SES light on your OBD II car would come on for incorrect fuel tank pressure.