slow 68 cuda help plz

[Rulito]

Hi, first of all, excuse me my bad english.
Originally i had a 69 barracuda with 2 barrel factory intake and factory carb, points ignition, 4 speed trans and 3.2 gear on a danna 44, i went to the drag and the 1/4 mile was on 16.3 seconds. Then i change the intake to a Weiand X cellerator and a Carter 600 cfm carb, Crane Hi-6 Ignition, 3.73 gear, i welded the diferential in order to obtain traction from both wheels, i went to the drag again and i get 17.5 seconds!!!...
i have a factory cam, but today i received a new 274 comp cam and im planning to make a dual exahust system, so.. the question is.. why my car get slower than before?, what can i do in order to be faster.
Thanks for your atenttion

[power ram man]

whats the block size ? could that 600cfm carb be too mutch fuel for a small v8?
then you weilded the spider gears/ i would have chose a mini spool. the weild could be causing too mutch drag along with weilding spiders your more prone to lose traction off the line altho with too mutch fuel you cant fully put to use the new intake (i also aske one of my buddies certified master mechanic he says get a o2 sensor with a fuel /air ratio guage to moniter your ratios for too mutch fuel) i think the 600 is too big a 500 or eaven a 550 cfm would be fine if one of your buddies has one try to borrow it see how she runs

good luck