85 D150 rear swap question
 

Hey guys,
I was wondering if i could get a little better highway milage and is it possible to change from the current 8.25inch rear to the 9.25 and run a 2.73:1 ratio. Back in the day my brother had a 72 charger with this rear and it reved pretty reasonably on the highway, just a little lazy off the line. I dont know what is in the 8.25 now because someone removed the tag but it reves on the highway!!!

Yeah you could change gearing but find out what you have now. It may not be that far from what you are referring to. Be careful if you put the taller tires on it. This effectively increases the gear ratio {lowers it numerically}. You may need at least 3.23's if you put taller wheel and tire combo on it. I wouldn't change it unless you got 3.55 or better. {like 3.91 or 4.10}

You can count how many ring gear teeth you have and divide it by the number in pinion teeth. That will tell you what you have. It should also be stamped on the ring gear. You can also turn the yoke and count how many times it turns with compaired to one tire turning one full turn.

How tall are the tires that you plan on running? what is the rest of the drivetrain that you have also?