I put in a gearvendors OD last winter , so far I have to say it was well worth it

BigBlockMopar said

What kind of ratio's does the GV have and what speeds are you driving normally?
Reason for asking is I have a installed a A518 OD in my '73 Dart and don't come close to the rpm you are still running on the highway, even with my 3.91 gears in the rearaxle.

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I drive between 70 and 80 mph , depending on the flow of cars on the highway , @60 mph 2300 RPM 70 MPH 2600 RPM , 80 mph AROUND 3000 . Makes a big difference at $7.00 a gallon(1.71/litre) , today I drove to montreal 51 miles and 51 miles back and it took less than a 1/4 tank (15.60 to fill it back up ), without the OD it takes a little less than 1/2 a tank .
25" tall tire 3.55 GEARS / WITH OD on in 3rd they equal 2.77 gears .
Calculator for estimating speed with dif gear tire combo
http://www.bigblockdart.com/forum/speedtire.php
http://www.bigblockdart.com/forum/speedtire.php