Ford put DOCs (Diesel Oxidation Catalysts) on certain 7.3L PSDs, not DPFs (Diesel Particulate Filters).

People have removed a lot of things from 7.3s, but no one has ever removed an OEM DPF from a 7.3.

What folks removed was a DOC, which was a through flow oxidizing catalyst.

The O is the verb of the DOC... oxidation.

The DOC oxidized carbon monoxide into carbon dioxide.

The DOC oxidized nitric oxide into nitrogen dioxide.

The DOC oxidized gas phase hydrocarbons (HC) and some of the soluble organic fractions of particulate (PM) matter into carbon dioxide and water.

But the DOC wasn't that effective at arresting particulate matter... only a relatively small fraction of it.

So along came the DPF (introduced into Ford diesel production after the 7.3L was retired).

The DPF flows like the AIS air filter. A hunk of honey comb shaped channels, all immediately adjacent to each other, where each channel has either an entrance, and no exit... or an exit and no entrance. Nothing can flow through the channel's axial orifice like one might drive through a tunnel, or like water might flow through a pipe. Instead, imagine water entering into a pipe, and then having to permeate through the wall of the pipe in order to get into an adjacent pipe in order to keep flowing. That's called "wall flow."

A DPF is wall flow.

A DOC is not. Rather, the DOC is through flow.

A DPF can get filled with PM... as the dead ends of each tunnel pile up with soot that couldn't permeate and pass through the wall. When these channels fill up enough, sensors trigger the vehicle to go into regeneration mode, elevating the temperature of the exhaust to cook the pile ups filling the dead end channels down into ash.

A DOC is a reactive chamber that has channels, but these channels are open at both ends. A DOC can become face plugged, but not "filled" like a DPF. There is no periodic regeneration of a DOC, other than replacement.

The DOC is literally a catalytic converter, with different catalysts to promote different chemical reactions with the exhaust.

The DPF is an exhaust filter, to reduce the particulate matter that we otherwise must filter with our nose hairs, snot, and lungs.

It is the cooking of the DPF to regenerate it that caused flames to shoot out of the tailpipe back in 2007. The dualing of the outlet tip alone was not enough to distribute the heat jet blasting out of the tip (due to faults in the programming, addressed by recall 07S49) The relief cuts at the tail pipe leverage the flow of the exhaust to draw in cooler ambient air to mix with the exhaust just prior to exiting the tip. I've been wanting to add one of those dual relief cut tips to my 7.3L for well over a decade, but never ran across one. Now @brokestroke has stolen my thunder and beat me to it.

Neither the DOC nor the DPF use any DEF (Diesel Exhaust Fluid). DEF is used for the SCR (Selective Catalyst Reduction) to further reduce the nitrogen oxides generated by combustion.

 

There is a cuff just upstream of the tip that "sucks in" cooler outside air - all of the dilution doesn't just occur at the slits in the tip.

Ford's execution of the passive cooling was way more aesthetically pleasing than GM's for sure.


I made a similar exhaust for my 2000 2WD using the 3" tips from a 2nd generation Lightning. I had to remove them once the axle anti-wrap bars went on.

 

Those newer motors would get a little better if they did away with the EGR went entirely to exhaust aftertreatments to meet emissions. I remember reading that Cummins could supposedly do this back around 2016. They do a lot of the R&D on the emissions stuff as I understand it.

 

In the meantime, Ram's solution:

 

That's only in the mornin'!

I remember watching that on streetfire.net in 2001-ish.

 

Gotta have that ‘woooo WOOOO’!

Classic.

 

I did notice my whistle turned more into a "woo-woo" but only on cold starts in the morning, and around here everyone is already up cooking breakfast.

 

California...where all the smartest and dumbest people on the planet live.

 

This oughta give a nice woooo WOOOOOOOOO