Disappointing #'s?

Ran my car for the 1st time on the 1/8th this weekend. It ran a best of 7.68 sec at 88.6 mph w/ a 60' of 1.67.

Using this converter:
http://www.hotrodpitstop.com/tools.html#3
a 7.68 1/8th would be a 12.06 1/4. Using that and the fact that my car weighs 3580 lbs (w/ me) it would take 395 HP. I was hoping for more then that w/ the following build:

440 6 pack
.030 over
9.5 comp
274/286 cam w/ .488/.491 lift (.521/.524 w/ 1.6 rockers)
lightly ported 452 heads
headers
MSD ign
4.10 gear
727 w/ 3000 stall
slicks (no traction problems)