On a hard launch, gas pours out of the gas fill cap (this is a 67). The cap is brand new, and the seal is perfect. I have a rag stuffed in the filler tube for now. It works, but I am afraid that when I spin the 540 to 6600 that rag will stop the tank from venting properly. I can't be the first to have this problem. Anyone know the fix?

I had the same problem on my 67 with one of those locking bowie tie gas caps. I bought it off of eBay for $20. They're junk IMO. I got a factory reproduction cap and the problem was solved.

The one I just installed is a factory reproduction cap from Rick's. Any other ideas?

My reproduction cap is also from Rick's. Is your filler neck in good shape? How full is your tank when your launching? I only have about a quarter tank at best when I launch, but I also have a sump on my factory tank.

I went with a fuel cell due to always hearing "stuff" from the track guys.

Is your filler neck in good shape? How full is your tank when your launching? I only have about a quarter tank at best when I launch, but I also have a sump on my factory tank.

My filler neck is not new, but it is in very good shape. I do not have a sump, so I make sure to keep the tank at least 3/4 full. I went to great lengths to keep this car as stock looking as possible, so I didn't want a sump hanging off the back of the tank.

Looks like its time to invent a solution.

put a late model neck on it that has the "trap door" thingy in it and a non vented cap.
then just figure out how to add a vent to it. maybe tee into the filler neck with a looping piece of hose with a one way check valve in it to keep fuel from spilling out.

On a hard launch, gas pours out of the gas fill cap

I also had this problem, looked like I was leaving about a pint of fuel at the line. Cap was a new repo, so I replaced the filler neck that looked ok. The cap then fit tighter.
I still see some fresh fuel stains on the paint (below the cap) after a day at the track.
But in the vidios taken from behind the car, I'm not seeing the fuel spash out on the track,
see this vid http://www.youtube.com/watch?v=HFiVc0Kbqpk
Tank was 65 to 70% full.

hb,
That used to be pretty much normal at the track when those cars were new. I dont know if there is anything you can do about it other than maybe keep the tank about 1/2 if you know you are headed to the drag strip.

I have the same problem. What I have done is if I have a full tank I put a plastic sandwich bag over the cap and filler neck and then put a rubberband around it. I may later find an ounce or two of gas inside the bag. At the very least it keep the gas from spilling on the car or the ground.