Your won't know till you run a back to back test, but odds are, you won't see much difference going from 3:23 to 3:73 with your 408.... I have ran a 3:55 gear, swapped in a 5:13 and the car ran the EXACTLY same et
Oh God, I hear you 100 % most people will not believe you but doI , I swapped 3.23 for 4.10 and they actually felt the exact same, I did not feel any difference let alone that "Smash" off the line with the lower gears (4.10) Even on the highway wasI doing about 2500 (give or take 1-200 rpm difference) at 60 mph.
Finally someone who see what felt.
