To FPD or not to FPD
 

I know many of you have eliminated the FPD but the debate continues as to the need of the FPD. Since I am currently in the process of doing my fuel system and I believe that the FPD is necessary for high pressure and flow applications (above 50psi going to 850,1600), I'm going to use http://www.injector.com/fueldampers.php

Just wondering if anyone else have used aftermarket FDPs and which one they used.

Yeah, it's a tough call. I've eliminated pulsation dampeners on TurboII's in the past with a banjo bolt with no ill effects, but there's still that nagging in the back of my head that Mazda wouldn't have put it there for no reason whatsoever. That, and the 787B Lemans car actually had a pulsation dampener on the fuel rail - there's gotta be something to it! :)

That's cool that Marren is making an aftermarket one, though.

Dale

Wow, at first I thought there was no alternative, just the downward spiral of replacing the OEM one over and over again... :( I didnt know anyone had eliminated it -- I thought of trying but was worried of the ill-effects.

I'll have to keep an eye on this thread for when the 'masters' get involved with some tid-bits of info.

EDIT: The Marren one looks a bit more resiliant compared to the stocker as well as costing the same.. I may invest in this little guy.

~Kris

how do you know when it has gone bad?

You can smell it in your engine bay... if you have a bad sense of smell I'm sure you can also tell when your engine bay is on fire.

I changed mine at 100k miles. Considering what I spend on fluids, maintenance and GAS, $100 is worth the piece of mind.

Trexthe3rd,

Are you upgrading your fuel system or just over-hauling the stock system?

If you are upgrading, some FPR's like the SX unit have dampening capabilities built in.

whats the fpd for anyways?

Fuel Pulsation Dampener

It helps maintain the fuel pressure in the rails at a constant rate while the injectors constantly open and shut. If you understand hydraulics it essentially functions as an accumulator.

I'm a firm believer in never eliminating something if I'm not absolutely and completely sure. I say leave the FPD in and replace it every 5 years or so to be safe. Many aftermarket FPR's also have this built in as mahjik said.

Eliminated it...Aeromotive

I eliminated mine with no problems. But I have since went to a SX fpr, so as far as long term use without it, I cannot say... I only had it that way for a few months.
If you are upgrading your fuel syst. then get an adjustable fpr and then you don't need your stock fpd.

ohhh, I should have just thought more about the name! haha it dampens the pulsations created by the pump to ensure a better flow out the injectors! hahaha it's been a long time since engineering school :bigthumb:

don't know if this thing would work with an FD, but check out this aftermarket FPD
http://www.injector.com/fueldampers.php

I wanted to eliminate mine and change to SS lines but when I was ready to order the replacement peice, K2RD went offline. Can someone ask them to work weekends or something?

Nice job buddy, check the first post in the thread ^^^^.:D

I am upgrading the entire fuel system and using the Aeromotive FPR (the one pictured in dubulup's post). The only thing I'm concerned with is this, the FPR has to be situated on the return side of the fuel system to work(after the fuel rails), while for the FPD to work it has to be before the fuel reaches the injectors. So how would the FPR compensate for the pulsation (after market or other wise) if it is installed where it has to be?
Technically I can not see how the FPR can act like a FPD. I know there are aftermarket fuel rails with FPD built in (for Hondas etc.), didn't find one for the FD. But the operating principle is the same, the damping is done prior to reaching the injectors in conjunction to the FPR after the injectors.
Personally I'd rather be safe than having to regret not putting in a 150 dollar part.
By the way, the FPD I found is easily rebuildable so no more worries.

So your saying the Aeromotive has FPD capabilities built in. That would be cool because I have that FPR. And I will remove the FPD then.:)

DOH! I was on there for a different reason and remembered this thread.

I'd like to learn more about this for the future...lets keep this going

I'm curious to hear from someone else who has studied fluid systems. I took a semester of tranport theory and based on the ss flow equations, I just don't see how ANY FPR can act as a FPD being downstream of the fuel rails.
In low pressure and low flow system (such as stock) it wouldn't be a major concern, but with almost 5000cc of fuel at 50-60 psi of pressure, pulsation can be deadly under wot conditions.

Just got the new FPD in, will be going through the fuel system upgrade (already installed the new Nippon Denso fuel pump). Will keep a picture log of the process for anyone interested. The picture shows the approximate location of the FPD to the primary rail.

Here's what the new setup should look like when finished.

What parts would I need tro order just to use the Marren FPD in place of my stock unit?

I worry of nothing more than I do an engine fire so any alternative that is safe over the stock unit but wont effect my fuel delivery system is a + in my book. I'm gonna redo my vac lines next weekend so I planned to either order the stock replacement and hope for luck or to get the Marren unit.

Thanks,
~Kris

The Marren FPD has a 3/8 NPT input. What you'll need to make it work with the stock system is somewhat involved. To start with, you will need to tap the primary fuel rail with 1/4 NPT tap. From there you will need a 1/4 NPT to 6AN elbow and a 6AN tee. You will also need a 3/8 NPT to 6AN adaptor to the FPD. The last thing is a 6AN barbed hose end to mate with the stock fuel lines.

Ahh Jesus--- I may as well just get the stock FPD and sleep well until I can afford to upgrade my entire fuel system. :( I'd consider a new FPD from Mazda safe for say another 60k right?

Thanks for the quick answer, I'd love to see how your setup turns out when complete.

~Kris

Step one is complete.
1/8 in has been milled of the top of the primary rail to accept 850cc injectors.
The inlet side recieved 1/4 NPT tap for the 1/4 NPT to 6-AN elbow adaptor.

Can the Marren fail like the stock FPD?

I suppose given enough time anything is possible but it is very unlikely. I looked at the diaphram inside the Marren FPD and its pretty damn sturdy, besides it can be rebuilt easily and only costs a few dollars for the replacement diaphram.

Ok, I just had a milled primary rail with 850s installed and a pulsation damper...also Secondary rail with 1600s...(I thought "Damper" was wrong but I looked on the box and Mazda says its Damper not "Dampener") However, I have the SX FPR...Do I need to have both?

That is the question I had and the preliminary answer based on some steady state flow equations shows the damper is needed. Especially with the larger injectors and higher fuel pressure. Untill someone who is an expert in fluid dynamics rejects my findings, the answer is yes, both are needed.
Of course many people will tell you that they have eliminated the FPD without a problem, but the final choice is up to you.

Trexthe3rd, the pic u posted of the fuel setup, is that just to usde the Marren FPD? Or is that just a setup you will be running?

Hi evryone... I know thet is an old post but I would like to tell my opinion on that.

Maybe I am a noob here, but I know something about fluid dynamics. The fuel flow in the primary and secondary rail is not steady state, but it is transient (time dependent). Totaly different behavior of the flow. The pressure wave is caused because of the opening and closing injector and then it is traveling along fuel rail. The bigger the injector is and with that the fuel flow, the bigger the pressure (shock) wave it will be generated.

In my opinion, for that the FPD would be placed closer to the second fuel rail not to the first. The FPD will then be more effective of removing these pressure wave and they would be removed quicker, because of the path that it is smaller. That way the total (static+dynamic) pressure would be constant, thats what Mazda want to do, but they placed FPD before the first rail, whatever.

The FPD may be considered to be placed in the fuel system when the fuel flow is great (also short duration betven two injection) and when the amount of fuel to be injected in the chamber had to be precised. Because these pressure waves can couse undisturbed amount of fuel that injector injects.

The other thing is that the FPR can not damp these waves, because the pressure is dynamic, not static. On the other hand if the FPR have build in FPD the stock FPD is no longer needed. Because the FPR with build in FPD regulates static pressure and eliminates the dynamic one. That way you will be fine.

Someone that is freak in some way would say, why not put FPD before and after each rail.... that way the dynamic pressure would be removed even quicker, but what will you get wit that setup, will it be worth it?

So removing the FPD will actually hurt the engine how..?

As a past career hydrodynamicist, I fully agree with these statements.

As to a Pulsation Damper need in an RX-7; who really knows .. but I will add these comments:

1) our cars run high rpms, creating very high frequency injector pulsing,
2) they batch fire, again increasing pulsation frequencies,
3) the primary and secondary rails are separated so even if an aftermarket FPR provides some high frequency damping (it obviously does low frequency by its very nature) it is a very long way from stopping primary pulses from creating shock waves. Since the fuild flow is subsonic, pressure waves (traveling at speed of sound) travel both ways.

Alternative to the FPD?
 

Might be a dumb idea but if you were to remove the Mazda FPD, which I understand is prone to failure, and instead installed a fuel pressure gauge at or near that point could the gauge do double duty? Give you fuel pressure readings and mitigate the shock in the fuel system due to the injector opening and closing cycles? It would seem that the mechanism which allows the needle to move based on pressure is similar to the function of the rubber diaphram in the FPD.

Jeff

^I wouldn't exactly call it "prone to failure". Yes it will fail given time, heat and usage. So will every other mechanical device under the hood - solenoids, sensors, hoses, wires etc. My replacement FPD has lasted many years and miles now.


As for your idea, a gauge probably has not have been designed to absorb those kinds of pulsation frequencies and probably won't perform the same task as a pulsation dampener as effectively as the FPD.

or you could just get an aeromotive FPR that has a pulse damper built in.

http://www.rx7store.net/product_p/aeromotive%20fpr.htm