I have a 83 F350 DRW and I am putting a ZF 5 peed in. I am also putting new diffs in front and back. trying to get rear gear for for highway, and I have a set of 3.55s that would have it turning at about 1800 to 2100 during normal highway driving. Is that a good gear set up/cruising speed?
I am going for MPG and towing, I have no problem down shifting at every hill towing if that is what it takes it get better MPGs.
thanks
bill

 

I ran a small fleet of F250HD's towing ridiculous! loads on gooseneck trailers from the late 70's to the early 90's. The sweet spot for 460's mileage seemed to be 3.08's direct running solo but most of ours were 4.10's. To many RPM's is overspeed, too few is lugging. Not sure what the OD ratio is on a ZF is but you can go from there.

 

thanks, I think the ratio on OD is .71 to 1, same as a E4OD.

 

I have 4.11 gears and a e4od and I have to much gear .gas milage falls off at anything faster than 65 mph.
I need to change gears in mine also.

 

'85 460 w/ 3.55 & C6........best cruising rpm 2300 to 2500
Any higher and it feels like you need another gear. 2500 rpm is about 65 to 68 MPH.

 

NEVER tow in OD. It stresses the engine as well as the rest of the drive train.

Best towing RPM is ALWAYS at peak torque.

That said my 1984 F250 with 460, C6 and 4.10s at 2800 rpm is right at 56 mph. Going slow is a major mileage improver. If I run over 60 mph I get 7.5 mpg or less. Slow down to 55 to 58 mph I get 9 to 10 mpg. Both of those numbers are with no camper, just the dually flatbed ATV trailer.

My 1999 Ranger with 4.0, ED and 3.55s tows best in 3rd gear and on hills in 2nd same trailer as above. Alone in O/D the truck gets 24 mpg highway.

 

why? I always tow in OD on flat ground.
If I have to give it more than 1/4 throttle, I down shift.

 

Me too but the majority of guys towing out there aren't as smart as you either.

 

Adding a vacuum gauge in the cockpit would help people understand the load applied to the engine in OD.

 

TOTAL AGREEMENT! This could be called a 5-Star Statement. On the right side of Clyde's steering column is mounted a vacuum gauge, on the left side a tachometer (haven't gotten around to installing the in-dash unit I scored off a neighbors Bronco before it went to the junk yard).

In a nutshell; higher vacuum readings=more efficiency=better mileage. It is amazing how much difference a "lighter foot" can make and this little gauge can show you how. Cruise at a given speed and you'd be amazed how much vacuum you can increase and not lose speed. I've also added a micro switch and a cowl mounted indicator light to let me know when the secondaries start to open. Then I can decide if I want to back off or go for it.

With basically the same setup that Bear is running; under normal wind conditions, watching my gauges and my speed averaging 57-60 mph, I can run 7.4-7.8 mpg TOWING my 10,000# "wind anchor" and I'm not a "flatlander". Using the vacuum gauge I go slower up hills trying to maintain 5-7" of vacuum and I go faster down hills taking advantage of gravity. I lose if I try to set a faster pace and we generally avoid freeways when we travel preferring the shorter route to the higher speed.

 

In addition to adding a vacuum gauge, it is helpful to know what the power valve opening point is (6.5, 7.5, ect.) Keeping the vacuum level above the power valve opening point will help with MPG.

 

My "Carb Guy" reinstalled the OE 4180 dual stage power valve on my last rebuild. I need to ask him this!!! Thanks for the thought beetle!!

 

I always run a dual stage power valve in my tow rigs. But I doubt very much it is the same value as the 4180, AKA an emissions carb and not a mileage or power carb and I removed it as some as it was feasible. I found a properly set up Holley 4160, LIST-1850, 600 CFM carb increased power and mileage by about 1 1/2 mpg.

 

Sounds good Bear, but if my "Carb Guy" Pat told me to cover the outside of my carb with chunky peanut butter I would likely have a messy engine that smelled REAL GOOD when it got warm.

Before the last rebuild we had a long discussion on replacing the OE carb with something else. Pat knows my truck, my truck usage and as far as I'm concerned damn near everything there is to know about carbs. IMHO (and many others too I might add) he is the premier carb person in Minnesota ... whatever that is worth in the international scheme of things ... and also my friend.

The 4160 may do well for you, but as I stated, I'm doing mid to upper 7's towing a 10,000# windanchor and I'm smilin'

 

The 4180 has several "BAD' traits, one of which is a too lean idle no matter what you tune it to. Number two is the backwards idle mixture adjustments. Another is the ported vacuum system works weird and I don't like how it advances the timing.