Pressure build up in Gas Tank

[Fuglee]

Hey all,

I have a 88 mustang 5.0 heads, procharger and whatnot.

Lately I've been taking it to the local track to run lapping days. The car runs great and strong but there's a problem.

Pressure is building up in the gas tank. One time, after about 10 laps, I began to smell gas. I pulled over and gas had backed up and was spilling out around the cap. I took off the cap and let the pressure out.

Someone suggested that I buy a new gas cap as mine wasn't venting properly. I did that and it doesn't seem to make a difference. I also checked the fuel tank vent forward to the charcoal canister and it is clear.

After running the car yesterday the problem seemed to have dissappeared. There was no pressure in the tank, I checked after every 10 laps or so by taking the cap off. However, once the gas level dropped to about half a tank, it started building pressure again.

I haven't heard of anyone else having this problem. It seems to me that the gas sloshing around the tank so much is probably the cause and is why it doesn't happen when the tank is near full.

I've thought about switching to a fuel cell but would like to avoid that if possible. If anyone has a fix in mind i'd love to hear it.

Thanks guys,

Fugs