I went to 3.08, TH400. IMO 3.90 unless you have a manual tranny is good for the track and burnouts, for a good all around and still be able to take er up to 120mph I would recommend to stay at 3.55 or a little below. There is a table out there that calculates the RPM in any speed with your gear ratio installed. That's what I did when I picked mine. You have to tailor to your driving habits and desired outcome before you pick. With my 3.08 I can take my car up to 160mph and still be a tat under where redline starts, but if you never go above 100mph the 3.90 is good, but you would redline probably at around 120mph with an AUTO Tranny. And unless you like high pitch whining noise, lower gear rations are better on the ears. Last but not least, think about what you're gonna do with your engine.....it all affects gear ratio, everything has to work together....
