Want to swap out the gears in my '89 F-350 dually. Has the 7.3 idi with the ZF 5spd. Didn't some of the automatic transmission utility vehicles around that year at least come with 3.42 gears? The 4.11's are really not needed. Don't haul any heavy loads. What vehicles should I scout out when 'touring' the junkyards?
VT247
Quote:
Originally Posted by cleanspeed1
The old IDI 6.9/7.3 in that chassis will do in the 14-16 mpg range all natural, will do better if turbocharged with either the factory ( nee ATS ) or a Hypermax system. The biggest problem with these engines is simply gearing.
From the factory, these engines are geared too low, and if the gearing were changed to lower the speed to 1600-1800 in top gear at cruise, the mileage goes up substantially.
I used to frequent an IDI site, and one of the founders took a stock 6.9 IDI and a 5 speed OD transmission and put it in a F150 pickup with 3.08 gears in the back. Got 30 mpg out of it. 
If there was a gearset in the 2.73 to 3.08 range for the 3/4 to 1 ton rear axle that was readily available, buying an IDI truck would be an mpg dream |