Alright, guys:
What changes were made to the 7.3 IDI between 1987 and ~1990?
See, I've got a 1988 F250 extended cab as my main truck. I've got a second 1988 F250 extended cab parts truck, and my parents have a third 1988-1989 F350 single-cab truck.
All of these have a 7.3 with a ZF-5.
All of these trucks look identical, more or less -- the parts are the same, the belts are the same, etc.

I recently(as in, over a year ago but never used it) picked up a little 1988 F250, single cab.
The sticker, the information all says 1988.
But this truck is different:
The 4x4 hubs are smaller than all of our other 88's.
The transmission and transfer case both has '87 on them.
The engine is a 7.3, according to the sticker.
However, this engine is a /lot/ quieter than our other trucks. I took the stock muffler off it, replacing it with my old Thrush Turbo muffler that I had on my main truck, it's far quieter than that truck ever was.
Now, I know this isn't fuel -- I've swapped the IP and re-timed it, and even when it's too advanced and clattering, it's still 'quieter'/smoother than all my other rigs!

And it shouldn't be -- the other two working rigs both have turbos on them(quieting them down, especially at idle), and this one is NA!

What I want to know is why?
Were there some changes that happened between the first 7.3s and the 88 model year? Perhaps injector distance/pre-cup changes?

I'll see about doing side-by-side video comparison this weekend if I can.

Any thoughts?

 

did you swap injectors with the ip?
Other idea if the rockers and push rods are worn would make it different

 

88 was the first year for the 7.3. 87 used the 6.9
88 to 91 7.3's are the same. the only difference would be HP ratings, and that number can be found on the driver side valve cover tag.
the small locking hubs are because that truck has a dana 44 IFS front axle.
the larger locking hubs tell it has a dana 50 IFS front axle

 

I don't know what makes one IDI quieter/louder than another, but I know what you are talking about. My '84 6.9 was super quiet, it almost sounded like a gasser it was so quiet. Never checked the timing in it, but it had to be good, truck got good mileage and plenty of power.

When a friend later bought a pristine '88 we noticed in the cab it was a LOT louder than mine, it rattled like a Detroit. And one would assume the newer body design had better insulation then the old.

As far as your smaller hubs, have you compared the GVWR for all the trucks?

 

That makes sense.

That sounds very similar to mine.