I have a VX differential assembly (3.25 FD) that I want to add to my D16Y7 transmission which has a 3.7 FD. The reason I'm swapping is due to a nearly broken differential, and I want to increase MPG. The problem is that I'm getting mixed opinions on weather a VX FD will actually increase mileage due to engine efficiency at low RPM. Maybe I will receive no gain, or a decrease in MPG at "x" highway speed.
Well, here's the thread where we're discussing it. Most everyone agrees that high RPM seems to produce better MPG.
Cool B-series differential swap vid. - Page 2 - D-series.org