4.88 or 5.13s are believable gears for an 1/8 mile with a Z. We had a couple of guys running 5.38s in SBCs at our old track.
There was one guy who ran a 5.13 in his SBC '61 Impala, and ran 1/4 mile. The car was named "The Twister", for obvious reasons. If I recall correctly, he hit the traps at around 8200.
