Okay, I've finally got the funds to do something significant with the 3.8L. I'm having it regeared soon and can't decide whether I should go with a Hemi swap, or a supercharger. I know the obvious answer here is probably HEMI!, but not sure if I want to drop the 10-15k on it.

Also, any advice on which gears to go with WITH a Hemi or supercharger? Want to go with either 5:13 or 5:38. I have an auto and 37's.

 

To a certain degree the choice of gears should be independent of the engine, although we use gears to compensate for weak and poor engine perf curves.

Look a the Engine performance chart (stock, HEMI, w/ SC), pick a nice torque plateau on the curve and select your desired cruising RPM. The go to the gear chart and find which gear ratio will provide that engine RPM at cruising speed.

If you want bias towards torque/power pick the next lower gear ratio (higher numerically) or if you a bias toward fuel economy pick the next high gear ratio.

The HEMI will allow you to step down a ratio or two do its torque curve (curve is shifted up and to the left compared to stock), while the SC depending on which one may not be too much different from stock because of its torque curve is shifted up but not as far to the left).