Ive replaced the fuel filler with a ride tech billet unit with a sealed cap. Gas tank is building a lot of pressure, I'm assuming I'll need to put a vent kit on it?
I just opened the cap and it nearly shot out of my hand there was so much pressure built up.
Thanks

 

The stock "vented" gas caps only vents in, not out, but the gasket might not seal the best against internal pressure. The gas tank building up pressure is normal, the difference now is likely because your billet filler and cap setup seals better than the factory one did.

 

Oops I didn't finish, lol. Since your cap isn't vented, yes you'll need to safely vent the filler tube (charcoal canister comes to mind), otherwise you'll create a vacuum inside the tank as the gas level drops.

 

Normal operation as road heat, exhaust heat, and ambient temp builds pressure in the tank providing the gas cap, as 69 states, vents IN but not OUT. OE design from GM.

The new cap will have to vent in allowing for depletion of fuel when driven.

 

Makes sense, thanks guys.
so pressure built up does not have any adverse effects on the fuel system? Wont create a situation where it could overpower the needles in the carb and flood?
The stock SS cap definitely did not seal tight (always a splash of fuel on the rear bumper from hard acceleration).... even though the gasket on it was new.

I guess my question would be; is there any issue with installing a vent that breathes both ways to keep the tank neutral without any pressure or vacuum? I understand the concern of fuel vapors in the garage but the poorly sealed stock cap wouldn't have helped there anyways.

 

Pressure inside the tank actually prevents gas from draining from the line and back into the tank as the car sits. But that wouldn't drain the closed off bowl in the carb and leave you with a no-start, engine might hesitate as the gas catches up though. I've never had enough tank pressure where it overpowered the seat in the carb, pre-emission carbureted cars have been set up like this for years. With that said, I don't see where you'd have any issue if you did vent the tank out, like how was done on smog era cars having a tank vent line to a charcoal canister. I would look into definitely having some kind of a safely placed fuel vent canister, as opposed to having an open explosive line venting freely into the air.

 

Since positive pressure isn't a concern I think I'll just run a vent line with a valve to allow air in as the fuel level lowers but keeps the fumes in the tank.