View Full Version : 3sge fuel rail upgrade for my 3sgte

07-12-2010, 09:52 PM
When I picked up the 3sge intake manifold (I am using the runners for a new custom manifold for my 3sgte) I also got the fuel rail with it... bonus. It will flow more fuel and I won't have to buy one or make one from scratch. I am planning to deadhead it.

Some particulars on my setup/goal:
-880 injectors
-350-400 whp capability
-Walbro in-tank already installed

So I was brainstorming on what the best way to set up this rail that will ensure even distribution/pressure to all injectors. Since the 3sge rail also came with a dampener, I thought I would include it in the plan. I realize that in some ways I might be overthinking this, or designing in a redundant fashion... but here goes. (I have read over the excellent threads by Sang and Karl)

From the fpr, have two -6 fuel lines supply each side of the rail. This will ensure that there is plenty of flow, and the replenishment will come from two sides, keeping fuel pressure as even as possible. Then, instead of a return line, fit the dampener right there at the return line location, or, plug that hole and drill/tap a new hole in the exact center of the rail for the dampener.

So. Will the dampener function in such an arrangement, being at the center of the fuel flowing from either side? It will likely have very little work to do, if so, but why not have it anyway? I have also picked up some 1/4" L-bracket that I can use to firmly mount the rail.

Any thoughts?

07-13-2010, 01:04 AM
Considering the size of your injectors, the size of the rail, and running the typical -6 feed line, you've got enough flow to supply fuel to your injectors.

Dual feeds are usually meant for those where a part of their fuel system becomes a restriction when they are looking to run more fuel, IMO. For instance someone running a -6 rail can't simply run a -8 line and call it good since their extrusion is limited to -6. So they run dual -6's to compensate. Or for instance, those running a stock fuel rail with bigger injectors. The tiny 4.5mm bore can be compensated by going dual feed.

Honestly, I would just run a single -6 with your setup and keep the damper where it's at.

Add to that, with the fuel flowing through an inline filter and FPR prior to entering the rail, I would question the need for the damper at all. But if you have it, might as well use it!

07-13-2010, 04:16 AM
One thing I learned from wildland fire. Water hammer. This is why they might have put a dampener in the fuel rail to keep this at a minimum.

Wiki link if you want to read about it. http://en.wikipedia.org/wiki/Water_hammer

07-13-2010, 05:31 AM
Also to note: I was under the impression that the fuel runs through the damper and then the rail via a banjo bolt? If that's the case, what would be it's effectiveness, if any, if placed in the middle of the rail?

07-13-2010, 09:11 AM
Ok, here is a picture of my rail. I am going to add labels to it as I understand more about how everything works. Let me know if I mix anything up, like direction of flow.

So fuel flows in via the largest fuel line, on the right, entering via the banjo bolt that has the dampener sitting on top of it. So, fuel is not flowing through the dampener, but rather the dampener can absorb sudden changes in fuel flow (from injectors opening/closing or fpr reacting, etc). The dampening occurs then right as the fuel enters the rail. If so, then the rail and its components will feel less shockwaves. If the dampener were to be placed in the center of the rail, it would absorp shockwaves at that location, but won't be preventing the shockwaves from reaching most of the rail and its components. How am I doing?

The fuel then flows through the fpr at the other end, with excess fuel being returned to the tank via the fpr. Where does the smaller banjo bolt and line near the center of the rail go?


07-13-2010, 03:59 PM
Sorry, that's what I meant by "through the damper". But, in any event, my understanding seems to be correct then, damper first, then into the rail. From what I've understood as well, the damper's purpose is to absorb the pulses due to the fuel pump, not because of injector firing.

Given that, I'd just get rid of it. The 3sgte runs without one and the only thing in between the pump and rail is the filter, your setup should be just fine considering it runs through both the filter and FPR now to dampen the pump pulses before hitting the rail.

Unless you want to use a banjo bolt to keep the damper in place, but honestly, i'd ditch banjos where I can.

Oh, and i've never worked on a 3sge before, but given the size of that line, I suspect is for a cold start injector.

07-13-2010, 04:11 PM
Sang's correct, the other banjo fitting goes to the cold start injector, usually sitting on the intake manifold somewhere.

07-13-2010, 10:47 PM
Ah yes of course, cold-start, forgot about that. Ok I edited my diagram with updated labels.
Ok, I will pick up some -6 elbows, and ditch the banjo's and dampener. I'll throw up a pic when I get it done. It probably won't go in the car for a while since I need to take car of the ems stuff first.

And thanks guys!

07-14-2010, 01:57 AM
as far as i've understood it, the damper is to compensate for injector opening and closing. there's an SAE paper floating around out there where they tested instantaneous fuel pressure with and without a damper. there were something like 10psi spikes and dips without the damper.

the flip side though is that the FPR acts, in a way, like a damper too. i decided not to use one on my setup and i haven't noticed any ill effects. i think the biggest thing is reducing restrictions in flow TO the rail so the pump can keep up with the injectors opening/closing. i would think that the damper is only really necessary if you're still running a banjo which would restrict the flow enough to need the extra damping.

07-14-2010, 04:29 AM
as far as i've understood it, the damper is to compensate for injector opening and closing. there's an SAE paper floating around out there where they tested instantaneous fuel pressure with and without a damper. there were something like 10psi spikes and dips without the damper.

Interesting, I think i'm going to have to see if I can dig it up.

07-14-2010, 10:28 AM
If that is the case, then there might be a benefit to running the dampener, even if it were threaded into the center of the rail. If it is simply meant to smooth out sudden changes due to injectors, it should still react in that location.

07-16-2010, 07:09 PM
Your PM box was full on the other board so I'll post it here:

You can get a set of injectors from fuelinjectorclinic.com for cheaper than what RC Eng sells a set for. Call them up and ask for a set of 4 drop in low impedance 7MGTE injectors. They are 11mm, top-feed, and should have the same ND oval clip to plug right into the harness. Judging by the prices they set for a set of DSM injectors, should be right around 325 for 950cc's and 345 for 1050cc's.

I made my rail using stock 440cc 7MGTE injectors.

07-17-2010, 09:34 PM
Thanks Sang, that's great info. What is used to seal the injector to the head, a cup or is there a good ring (like the viton etc) that'll do the job ?
I cleared up my PM inbox situation, sorry about that! lol

07-17-2010, 09:53 PM
I'm using the a cup (hacked off a gen2 rail) like Karl. I'm using an o-ring to seal the injector to the cup and a stock insulator to seal the cup to the head. Tarmac on the other board is using a THICK faucet o-ring to seal his 14mm injectors directly to the head.

07-18-2010, 04:04 AM
This is the pic tarmactrr sent me for his Siemens injectors. It would come down to dimensions so that the injector sits the right distance once its tightened down with the mount. What exact distance is correct? Or will that be obvious once I get this all in my hands and in front of my eyes? :) I have definitely seen such rings at harware stores. The Viton one is not conical... Where can we get those?


Ok, I looked up viton square-ring availability, they are everywhere, I can get some locally easily. I am also going to go a bit bigger on the injector, 1000cc, as long as I can get it to idle, it would be nice to not be pushing the limits anywhere... so have them at about 80% max duty cycle.

07-19-2010, 06:03 AM
I think FIC sells their high flow blue-max line of injectors up to 1500-1600cc's or so for the 7M. If you really wanted, you could drop the $800 for some 2150cc DSM injectors. You'll have to get new injector clips, or put together an adapter if you didn't want to splice.

But meh, depending on where you plan to go, overkill is just a waste of money.

Oh yeah, let me know kind of o-rings you decide to go with. Would make installing the rail a little easier. The cups don't quite want to stay in the bosses on their own. I keep dropping them :)

08-08-2010, 10:53 AM
looking at 7mgte fuel injectors on the FIC site, I wonder which injectors are "true" size and which are modifieds... for example, whether 1050's and 1150's are based on 950's, etc...
Or if 950's are based on 850's etc... I guess i can ask them when I call them...
Judging by the price jump between 950's and 1050's, they seem to be based on an overall different injector size.