What would the rpm difference be at lets say 65 mph with a car that has a th400 and stock gears compared to a 4l60 car with 3.73's out back. If I keep the 4l60 i need gears if i do a th400 with the tranny gearing can get away with the stock gearing with the set up I'm going to be doing. Basically wondering if no overdrive will be about the same as a geared car with od

 

Put your 4l60 in 3rd and don't let the converter lock. That's what a TH400 is like.

 

you can go to this site and play with numbers
http://www.markwilliams.com/calculators.aspx

 

still doesnt help i'll know what the rpms are like with the th400 and stock gearing but not what a 4l60 would be with 3.73 or 4.10 gears