Finished a few days ago swapping in a 7.3 IDI and zf5. Truck is and 85 Cab and Chassis F350. Had a 6.9 and 4spd. Today that ragged old truck with more than 1/2 a million miles saw 80mph for the first time in its life! Turns around 2750 rpm at 80 way gooder. Totally different truck. Yo soy muey contento.

 

Ain't that a wonderful feeling! Congratulations! I'd bet at 60mph you'll probably get a little better mileage too!

 

Figured it on Sunday. 15mpg not stellar but I'll take it. Put about 500 miles on it so far, going to good. Scarrey thing is, might be OK.

 

My '86 did whatever it runs on the governor with a C6 and 3.55:1 for over an hour except letting off for EGT on some hills, past the end of the speedometer and pushing 12 psi the whole time. Cracked one injection line on that trip (was missing a clamp), drive home was normal speed and it got 9.79 MPG on that trip, not terrible considering how fast on the way up and leaking fuel the whole way back. Now with a ZF5 it's averaging 14.5 MPG with mixed driving, up from around 11.5 Cruises happily at 70 MPH and 2000 RPM. So much nicer with a ZF5.

 

Mine loves speed. So do I. Sort of like breaking the sound barrier, the faster I go, the smoother it gets. Not even loud.

 

Mines got 4:10s so it has to spin faster to go as fast. Did that make sense?
But you are right the ZF make it a whole new truck.

 

Hey Herb congrats on the build. Sounds sweet. My C-6 has a Gearvender overdrive on it I do 90 at 2,800 rpms.