jdhuegel1

I've read around quite a bit and haven't QUITE got what I'm looking for (If I even really know what that is)...

I currently have my setup running in sequence. -6AN from hardline at firewall to Primary rail. From primary rail to back of secondary rail, and from there through the SX FPR and out..

I've heard that this is fine. Many people have run setups similar, but I have also heard people prefer a T on the feed line and parallel lines to the primary and secondary rails.

What is the real difference? Equal pressure at both rails? Any help explaining is appreciated.

clayne

Notice how this technical and thought out question just passes through the cracks of "how low is your fd dude??" and "my gauge reads 450 degrees, is it accurate?" threads?


Anyways.. I _believe_ it has something to do with the way the FPD works and injector flow dampening being an issue when running serial vs parallel configuration.

When the primary rail injectors are firing they are influencing the fuel flow to the secondary rails due to the serial nature. I'm pretty sure this is why the FPD is there in the first place.

Here is a decent snippet of information from another thread:

https://www.rx7club.com/showthread.p...hreadid=214151
https://www.rx7club.com/showthread.p...hreadid=246044
http://www.nopistons.com/forums/inde...0&#entry309962

You may also be able to run 2 pumps/FPRs with seperate rails, elimnating the FPD and preventing injector duty cycles on the primary from messing with the secondary. In addition it also appears there are some size differences between the two rails which affect the pressure:

https://www.rx7club.com/showthread.p...ing+fuel+rails

"You gain a far superior fuel pressure regulator. And running the rails in parallel means there should be no drop in the primary fuel rail pressure when the secondary injectors turn on."

There you go.

rxrotary2_7

true this does suck about people ignoring technical questions. but what are ya gonna do?
anyway, yes there will be a slight drop in pressure when your larger injectors upstream kick on, BUT thats where your FPR kicks in and starts to work levelign it out again. the transition between primary and secondary happens at a very light load point, where it may never have a detrimential effect on anything, thats why i think its ok to still run in a series. but i do *believe* it is *better* to run in parallel.

teamstealth

Quick question....why is the regulator after the injectors? I'm just thinking visually about my paintball gun since thats the only thing i know of thats regulated and all the regulators are before the valves. Is this to adjust for the 2ndary injectors coming on instead of just letting them use up a percentage of the pressure?

But to answer jdheugel1's question, it's better to run them in parallel because both sets of injectors will see the same pressure no matter what. It's probably more than ok to run them in series with the setup you have, but to be totally 100% safe, parallel cant be beat.
thats my $.02

-Zach

rxrotary2_7

ummm, because its FI'ed. how would the regulator work otherwise? the pressure needs to be between the pump and the injector really, so by having the regulator AFTER the rails (injecotrs), it can regulate the pressure between those two points.

jspecracer7

wow, a well thought out thread.

Either way, I run my dual stock FD pumps in parallel(obviously, one runs the 550cc's and the other runs 1680's) then plumbed to either side of the regulator.

I was a bit concerned that I wouldn't have enough fuel for my secondary injectors because as a stock pump, it's meant to handle 2800cc's(550 X 2 + 850 X 2) and I'm running 3360cc's of fuel out of the 1680cc's X 2.

My fuel pressure does seem to be fine at 15 psi, but if I go any higher, it falls off(45 psi static FP with drop off after 60 psi).

My question is: If I run a supra pump to the secondary rail and use the stock FD pump to run the primary's, do you think the FPR would be able to handle it. The gauge itself is at the FPR, but to be more accurate, would you think I would have to run 2 fuel pressure gauges(one to the primary/one to the secondary) to get a better fuel pressure reading?

Just some more thoughts...

teamstealth

thanks for the explination. lol thats what i *thought* it did, just had to draw it out in my mind!

Jspecracer7, i dont see why your supra/FD dual pump setup wouldn't work as long as you had a good FPR, but to double check it, i would do what u suggested and temporarily run a FP gauge to each rail. Redundant, yes, but better safe than sorry.

jspecracer7

yeah, problem with that is I have to buy a FP gauge and tap the rails to see what it's set at....too much work for now since the FPR has a 1/8th npt port for a FP gauge already installed

jdhuegel1

Thanks!!

jdhuegel1

Appreciate the info Keith!