Man, I get this one a lot.
Cobras come stock with 3.27s only. I run 4.10s on my car, which is my only transportation, and they work quite well. Initially I lost some milage, but after I learned how to drive with 'em I maybe lost 1 mpg.
A lot of other people people favor the 4.30, because it lets you run in 4th a little longer before the finish line in the 1/4 which helps pick up a little in trap speed.
With 4.10s or 4.30s people typically pick up around .3 in the quarter. A friend of mine went from 13.2 to 12.89 when going from 3.73s to 4.10s in his bolt-on only 96 Cobra.
Hope this helps.
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'97 Cobra, K&N, Flowmaster, subframes, 4.10 gears, Steeda Tri-Ax shifter, Steeda G-Trac 3, Cobra R wheels w/ Goodyear F1s
[This message has been edited by 97snakedriver (edited 05-02-2000).]