Ya. He'd done a cummins swap into an SD for a guy and kept all the zf6 hardware.

I've got right at $3k into my zf5 when all was said and done. It was a recent rebuild, I drove the truck it was in before it was pulled, and most of the accompanying parts where new.

 

zf 6

5.79 3.31 2.10 1.31 1.00 0.72 | 5.23

zf 5

4.14 2.37 1.42 1.00 0.77 | 3.79

gears 2-5 are very comparable. then you have 1st gear. i like the zf6 for the ability to use it as a 5 speed unloaded or lightly loaded. but having that extra low gear to not have to tear up the clutch when loaded. where as the zf5 has a nice compromise for 1st gear.

this is something i've been wrestling with my self. because i have the automagic, it's nice, it works, but i like to have control. and since i'm married gear changes are about all i can control. just kidding honey. also when it's time for a rebuild. i want to build the trans for more power, so $4000+ for a built automagic or $2500-$3000 for the fun of it?

for me the extra work seems worth it, especially if you're doing everything else to the truck. and i'm sure the power is not far behind. so upgrade as much as possible.

 

The E4OD 4th gear is .71. That's the only reason I think it might be noticeable. It was highly noticeable when I went from e4od to zf5 but I cruise the highway a lot. The rpm jump was enough to make a notable mileage difference and get me to swap from 4.10 --> 3.55. I don't know though if power loss through the auto's fluid makes it an invalid comparison or not. Then again, Brad has infinitely more experience with these trucks than I do so he's probably right.

 

...no fluid considerations with the TC locked. .71 is .71 on the highway, so the zf6 will be almost identical to the E4OD in terms of highway cruising, whereas the zf5 will be slightly higher RPM for the same speed.

lets see what 'slightly higher' means. give me a few minutes here.

OK - i'm guessing here as I don't remember exactly from before my swap, but if we say 2200 RPM gets you 70 mph with an auto OD or ZF6 5th gear (.71 ratio) you'll only be doing 64.5 mph at the same RPM with the ZF5 (.77 5th gear). or the other way, you'll have to turn 2385 RPM to do 70 with the lower gear ratio. so, you're looking at about 200 rpm difference in cruising RPMs between the ZF5 and ZF6/E4OD. again, this is just an estimate, and its based on my recollection of my E4OD days, with my 3.55 gears. 4.10 gears will see a more dramatic drop (going from ZF5 to ZF6) in RPM as their RPMs need to be higher for the same speed.

so, yes, not earthshattering, but probably noticeable.

related to this, I've noticed my boost pressure being slightly higher at cruising speeds with my ZF5 - like at 75 mph, i'm boosting 3-5 psi (depending on grade, wind, etc), whereas I don't really ever recall breaking 2 psi with the auto. with my truck anyway, I've noticed this RPM range - just over 2000 - is just where my old, tired, stock turbo really spools up, so with boost affecting PCM fueling, I bet there is a significant MPG delta between the two setups. ...not that I care a whole lot about that, but its interesting.

 

If my calculations are correct……
4.10 gears with 34" tires and a .76 OD cruising at 65mph you would see 2001RPM
4.10 gears with34" tires and a .72 OD cruising at 65mph you would see
1896RPM.

That is 105 RPM difference. Like I said, HARDLY noticeable

@70mph
ZF5 2155
ZF6 2041
------------
113 difference

@75mph
ZF5 2309
ZF6 2187
----------
121 difference

 

S5-47 is 5.08-0.77

S5-42 is 4.14-0.77

 

my bad .77 1% off

 

Maybe it's just me........
But other than being able to say you have a ZF6 in an OBS, I just don't get it...??
Go drive a ZF6 with your same rear gear and tell me you seriously think it's a better trans, for the cost and work for the swap.
Plus those things are like 3 times the size of a little ZF5, and more than double or triple the cost.

Just saying is all, I personally just don't think it's worth it, for any reason.

 

I'm right with ya Jim

 

It's all about what you want. Why would one spend more money to get a 24v cummins when we all know that the 7.3 is superior? Boils down to wants not needs.

 

HA. that is funny right there

Tell me how a 7.3 is Superior to a 24v.

As much as i HATE the POS shipping crate those 24V came in the engine is superior in just about every way to a 7.3.
there is a reason those 12 and 24v DOMINATE the pulling circuit and the drag strip

 

I was referring to the entire truck.

And sound. No cummins will ever sound as good as a 7.3. That's enough reason for me .

 

Ford is one of the Most expensive trucks out there. Chevy and Dodge they will take 10k right off the window sticker.

As for the sound, that is personal opinion. And I do agree with you that a 7.3 sound better

 

You get what you pay for. And it shows after 200k.

 

It's not about being able to say you have a zf6, or the pain it is to either row through 6 gears, or have it cost 2-3x more...
I don't see the point, just like most of you, to switch to a zf6 when you don't drive your truck much or don't tow anything.
The benefit to the zf6 is if you tow heavy you have the extra lower gear to start it going.
The only real benefit I see for the zf6 swap is for the people with 350 gears or those wanting better mileage. Then you get a useable 1st and it is more of a cruiser.
As example, my buddy and I lifted his e99 and put 37s and with 373 gears it is a more useable 1st with the tall tires. Before with 285s it was never used...ever.