Currently running my 69 dart 340/727 with 4.56 gears 275/60 drag radials. Car runs 12.0-12.20 1/4 mile. Maybe putting in my 408 went 10.80 in same weight car with glide. What gears do I need to slow this thing down to 11.50-11.80 with same trans tire combo.

2.94

What I did to slow my car down to run 10.0
stuff was put a mech throttle stop on it and
lower the launch and shift rpm... you can also
slide your throttle cable in so you only open
the throttle part way... if you change gears in
it you will be WAY under your torque point and
be forever in low gear... I used the trottle stop
on mine so I could run 2 classes and change over
quickly.. this is what I built to fit on the carb

I run a 408 also because it makes 52 more lbs. of torque than my previous 363 i was going thru the traps at over 7.000 I went to a 4.10 but I am only going thru at 5,700 I am changing to 4.30s pretty soon. My Dart runs 10.70s but I slow it down to run 11.50s with a setup pretty similar to Mr Ps. , I might add that my 60 fts. remained the same going from 4.88s to the 4.10s because of the torque. Heres a picture of my stop, I have been running it for 8 years now and it works well.

About 4 yrs. ago I broke the 5.14's I was running in my D50. The best pass at that time was a 6.34 @ 108 in the 1/8. I stuck a chunk with 3.50 gears in so I could go race and it ran a best of 6.39 @ 109 crossing the finish line in 2nd gear. It lost the half a tenth in the 60 ft. I am now running 4.56 gears. It needs something lower than the original 5.14's.