Frx is a metered return. The regulator is in the fuel bowl.
So the pump pressurizes the bowl and returns excess pressure. Then injectors take fuel from the bowl and then it loops around to the metered orifice and into the return line. I'd suggest bumping up the regulator spring for a tad more fuel pressure.

A regulated return will (sometimes, get rid of the fuel bowl) pressurize the injectors and then go to the regulator and then to return line.

Unless you're planning big power, I'd go with the frx. Because it isn't a bottleneck in the system anyway.

 

FRx is just an 'air bleed' by design. All it does is provide a path for some of the fuel (and pressure) that is fed to the heads to flow thru the heads and return to the tank. Fuel pressure is regulated at the fuel filter housing before the heads in this design.

RR places the regulator and fuel return AFTER the heads. This puts the full flow of the fuel pump thru the heads.

Neither has any advantage whatsoever on a stock or even modestly modified engine. These trucks run just fine with 100% stock set-up on up to Stage 2 injectors. The 'deadheaded' design has been proven to provide some starvation of #8 with LARGE injectors, because #6 fires directly before #8 and at high RPM's and max fuel consumption - there can be a 'vacuum' created at the end of the fuel rail. This has only been demonstrated by measuring CP's and using some pretty sophisticated technology - and AFAIK, has never been tested at the level of power us mere mortals will ever attain. Nobody ever made more power on a dyno with either option and any advantage is purely subjective.

These 'mods' came about after the infamous 'cackle debates' back in the beginning of the last decade. Its kinda funny how heated the wars were about the mere existence of this problem back then - but nobody even mentions it these days. The same kind of hype and hoopla applies to the quick-disconnect fittings on the suction-side of the fuel pump...

I measure fuel pressure AFTER the heads and it remains consistent - even when running 175cc injectors. My fuel system is also set-up in such a way that I can turn the equivalent of FRx on and off with the flick of a switch and in 170k miles, I have never been able to discern a difference one way or another. During that time, I have experienced extensive vacuum/air leaks before the pump and while air does make the injectors louder - once it is gone, everything returns to normal.

Certainly, extended introduction of air will shorten injector life - but consider of the 2 million 7.3 PSD's on the road today, very few have any mods and likely even fewer experience sub-par injector life.

Fwiw, the stock fuel filter does a good job of removing any air that may be introduced. The inlet is on the bottom and the return is on the top. The fuel must flow thru the filter media and out the BOTTOM of the other side of the filter housing to get to the injectors. The fuel volume introduced to the filter housing is magnitudes higher than the MAX consumption rate of the engine. Basic physics makes it difficult to get air to the injectors...

 

It does do more than remove air. Besides the not visible air I noticed a quieter motor, a smoother running motor, and a smoother throttle. I had a problem at low speeds of a on/off feeling fuel peddle when i first got the X. After the dead head fix my throttle control is smooth like it should be even at a near crawl.

After doing all my injector o-rings and having the heads drained, the fuel bowl drained, and all the lines dry the 7.3 fired right up on the first crank just like it would any normal day. At least I know the dead head fix works. lol

When I built mine I rerouted the fuel feed lines from the bowl to both rears of the heads and the returns from the front of the heads.

Now I agree it shouldn't be the first mod on the list and for some people not even considered. But if things like the low speed throttle on/off problem or if the 7.3 is a bit to loud for your liking the FRx should be on the mod list.

My dead head fix is on the first page of the link in my sig for those wondering.

 

I appreciate all the input from everyone. I look forward to jumping into this project one Saturday morning and eliminating some of the cackle. Hopefully with help of another FTE member, I will be able to jump on the hutch/harpoon mods next.