what are your mods?
those cars were junk when they came out and they're junk now. a 5.0 will split in half with that much power without serious engine work. a 4.6 is just a 2 valve so i doubt hes running a 5.4 out of a navigator or a terminator engine. sounds like hes talking out of his flowmasters.
theres some tool in my neighborhood with a SN95 cobra with a loud exhaust and stickers all over it, he revs it up by me all the time but wont run. i even went to his gas station job and called him out and still nothing.