Gas fumes???????

I hope someone can help. I have a 1952 Chevy truck that originally I had a crate 350 in it.I decided to pull the 350 and installed a LS1 motor. Ever since I installed the LS1 my garage fills up with some BADDDD gas fumes. I have made sure that all fuel lines are tight and theres no leaks at all.

Any ideas what may be causing this?

you smell gas fumes and the engine isnt running or is it after its been running that you smell them? If its after, then its probably leaking fuel through the injectors and into the cylinders. Run some injector cleaner in the fuel for a while and see if it gets better or have the injectors cleaned. Are you sure the orings aren't leaking on the fuel rail? If you have a two line/return type fuel rail you should check the regulator. Disconnect the vacuum line from the regulator and stick the end in a soda bottle or something, then start the engine and see if fuel comes out of the vacuum line. If it does, replace the regulator.

No, its when its not running. I can have the truck sitting in the garage not running and the gas fumes are so bad that you would be afraid to light a match! Theres NO leaks. I have checked everything!

I sure hope your hot water heater isn't in the garage. If so, manually raise the door a few inches to let the vapors out since they're heavier than air and will be at the floor level.

If they are gasoline fuel vapors there are a few things to check. Check all the lines, tubes, and connections for leaks. Baby powder will usually stick to any fuel residues. What type for fuel system are you running? You could be losing fuel from a filter, regulator or injector bleeding fuel pressure off. When you're noticing the fuel vapors in the garage, is it after you've recently driven the truck and parked it and then later you came out and smelled the fuel vapors? What kind of fuel tank or fuel cell are you using? Does it have an outlet and return? Does it have a vent of some sorts that is vented to the atmosphere?

There are absolutly NO leaks. I have checked the fuel system from one end to the other 5 times!
I dont notice any smell after i drive it. Its only after the truck has been parked in the garage for a little bit. I can go somewhere today, park the truck in the garage, and by morning the garage will be filled up with fumes. NO LEAKS!!!
I have a stainless steal fuel cell that i bought from brothers trucks. The return what we did was tapped into the fuel filler neck close to the cell, and its not leaking. It has a vent, but i have put my nose up to it and its not coming from that. You cant smell fuel at the vent.

my guess would be that the pintles in the injectors are dirty and/or leaking the fuel into the cylinders slowly after shutdown, bleeding down the fuel pump's pressure. The fuel vapors then bleed out the open valves, then through the exhaust pipe and/or through the intake manifold.

So what would you recommend?

I would pull the fuel rail loose from the intake and set it up in the air with the fuel lines hooked to it. I would then energize the pump and see if any of the injectors are leaking. Don't do it with the ignition key, run a jumper wire to the pump and then watch for fuel leaking out the ends of the injectors.

Why not with the key?

when you turn the ignition on it may pulse the injectors a couple times to prime the engine and the pump will only run for a couple seconds.