What is needed to build a 7 second (1/8th) street car

420ish Hp should put you there with a 3400 lb. car.

The main problem with gearing is, do you want to keep it a street car or gear it for the max benefit in the 1/8th. If you need the best of both then i would gear to hit the traps in 2nd gear. The 3.91 with a 27" tire should put you there between 6-6500 at about 94mph in 2nd.

These are just calculated guesstimates and would really need a little more info.