Seek and yea shall find... from my (and Shane's) friend and fuel injection gurus:



'Nuf said!!

Now don't say **** about my stainless hardlines!!!

 

Good **** Carlos! I love me some authoritative sources!! 👍

 

if i understand correctly..... please correct me if im wrong

the oscillations in fuel pressure that the fpd is supposed to rectify, are caused by resonant frequencies is the vacuum reference to the fpr. its a game of harmonics basically. the oscillations as he mentioned in an extreme case, dipped as much as 10psi which is HUGE if youre under any significant load. with the graphs he presented, those oscillations seem to only be a problem below 4000 rpm and for a short window. with the drag car he was talking about and with the map sensor example he used, making the vacuum line shorter was the solution to move those oscillations into a high enough frequency where it has no effect..... as he stated.

the conclusion i got from the video is that so long as you have a short vacuum line, the fpd serves no purpose as the resonant frequencies are out of the range where it has any impact on operation. he mentioned very early on as well that the fpd isnt the end all solution for fuel pressure oscillations either. what i find most interesting is what he said about map sensor vacuum lines. most modern ECUs have the map sensor built in and require a vacuum line be ran from the manifold to the ecu. in the case of the FD, that line could very easily be 3 or 4 feet. i cant say ive ever heard or seen anyone mention anything about oscillations in their map readings. of course its entirely possible the software accounts for this and filters it or just doesnt pick up on it.

in an effort to understand the fpd and the stance that its a necessary component, i give my understanding as it pertains to the information in the video. if i am wrong or i misunderstand a concept i ask that you PLEASE correct me.

 

<My last comment on this thread tangent>

While Paul gives a specific example to a general principle, I would caution against focusing too much on that one example. He uses the effect of pneumatic feedline to a sensor (e.g. MAP) and/or a mechanical control(s) (e.g. FPR diaphragm) to highlight the principle. But also note that he starts with the conclusion that the ideal FPD would account for the AGGREGATE vibrations/pulsation within defined (narrow?) harmonics. It could include the sources he highlights as well as possible large fuel pump and/or injector pulses (my speculation).

As for most modern ECUs having the map sensor built, in all of the high end ECU I know of, this is not the case. It's just a electric analog signal from an Absolute Pressure sensor. For that matter, modern OEM MAP placement is predominantly directly into the airflow (i.e. no connecting hose); no hoses involved. Coincidentally, this is something I'm still working on for my install.

 

I agree that a fuel pulsation damper is a good idea in theory, and I agree that Paul Yaw and Shane T are both very bright guys who know a lot of things that I don't. That said, I think I've seen at least one or two RX7 owners or tuners claim their setup behaved better after removing a Radium FPD from the system. It might take me some digging to find the examples, but I think it was mentioned here or maybe on the HPAcademy forums or instagram or facebook.