I personally can't see any significant reason to not use a fuel dampener, with EFI.

This is my setup...
https://youtu.be/QnyAi_dW5ug

AG.



Challenger on XFI

^ Very nice, looks great

most OEM systems deadhead to the rail/rails. I was fairly certain this was the case, but i wanted to double check before pointing it out. The concern is not about the heat in the fuel in the rails from being deadheaded. It's the heating of the entire tank of fuel over time.

the MPI 3.9L,5.2 and 5.9 gas engines have fuel pump modules in the tank with regulators built in. I don't know the year range, but a Corvette inline fuel filter/return regulator combo is and easy way and common way to retrofit an EFI fuel supply. I'm thinking part of the reason a lot of efi builds have the regulator close to the engine is because that is where it was located for use with carburetors. Plus it helps to sell a bunch more hose/tubing and fittings. If data logs show the pressure stays safe, it really doesn't matter where the regulator is.

Yes, newer cars are deadhead at the rail(s), already went over that. My point is, there were millions of efi vehicles made with rail mounted regulators and they aren't all on the side of the road from overheated fuel.

Most of the EFI cars of the 80's-90's used return style regulators. The newer stuff uses an on-demand style regulating system that controls the pump output to regulate pressure. Sounds simple but requires a significant amount of complexity for the EFI control system, such as a pressure transducers to measure FP and give feedback to the ECM and modulate the fuel pump. The computer will also have correction algorithms to correct for fuel pressure discrepancies that are inherent of those systems. I think there are some aftermarket EFI systems that have some capability but most tuners will still want to stay away from this in high HP applications.

So in general, if you have a return style regulator with a huge pump to support a lot of power, it will generate a lot of heat in the tank due to return flow recirculating but will generate the most stable fuel pressure and in turn, the EFI tune will be more stable. The work-around solution is simply to have PWM control on the pump to limit the amount of return flow and basically giving you the best of both systems. A lot of EFI systems have that capability.
AG.

Agreed on that, what works works. With a regulator mounted near the tank you need to make sure line size and fitting sizes are large enough to not have a pressure drop from the regulator to the injectors as fuel pressure will then drop.

(whereas a regulator mounted up front after the rail(s) would compensate for drop across the feed line and fittings if the pump has any overhead at all)

Agreed on all. I may switch my pump to PWM control, great way to go for several reasons.

I'm looking to do the same with Holley EFI Hp. The diagram from holley says FPR after the rails on the opposite side of the of the supply rail, is this how to run these? I'm using Stage V intake so I'm unable to pass through under the runners.
So my FPR in in the back on the passenger side being fed from the passenger rail.

Thanks, john.

Returnless EFI systems have good and bad trade offs. The good being a cleaner install. The bad... An engine that is required to idle nice at low RPM, yet makes very high HP, needs either the dynamic range of a intake referenced return system, or an electric feedback PWM pump. Without either of these things, the extreme ends of the fuel supply run into a wall. Most naturally aspirated engines wouldn't fall into this category of "very high HP'.
To size an injector that supplies enough fuel for max HP and still have enough short pulse width time, it helps tremendously to alter fuel pressure in the rails. Higher intake vacuum lowers fuel pressure for idle, and higher intake pressure raises fuel pressure for power. Doing it with a manifold referenced regulator, or PWM feedback loop system are both good options.

It sounds like you want to run a single feed, and have the rails feed in series with the FP regulator at the end of the rail. If so, This will work but is not optimum for HP applications.

AG.

I would agree with mounting the regulator in the back and a short return line to the fuel tank. Most returnless OEM systems that use a regulator, like GM LS engines use the fuel filter with a return line as the regulator. By putting the return line close to the tank you do not transfer so much heat to the fuel by returning from the hot engine compartment. OEM went to returnless systems due to evaporative emission concerns, hot fuel likes to evaporate. Most OEM's now use the computer to vary the speed of the fuel pump to regulate fuel pressure.