Bone stock 318 2bbl 1/4 mile?
My experience says those '85-up ones with the Roller cam and 302 heads run better than the older ones by quite a bit, so I'm not that surprised that you're able to run that time.
Now, you're going to need to hop that baby up some, as pretty much all modern cars will whip up on it. My '04 5cyl 2wd Chevrolet Colorado ran 15.8 @ 92 and the '12 Cruze I have will do a 16.0 @ 88 with a 1.4L Turbo engine with only 138hp and 3100 lbs to lug around.