83 Crossfire TA

iTrader: (2)

I need to make up some fuel rails and associated plumbing for a project I’m working on and usually I’m a form follows function guy but this time I’m debating. I’m trying to keep the manifold looking fairly uncluttered without a whole mess of lines running all over the place.

I know the best way to go is to feed one end of each fuel rail and run the other end of each to the regulator, and then back to the tank. But that way you end up with 2 lines going to the front, 2 lines going to the back and all the associated clutter.

What I’m seriously debating trying (but would hate to blow up an engine over some petty aesthetic stuff) is running the feed to the pressure side of the regulator, return to the return side and then run a line to each rail from the other ports on the pressure side of the regulator. The 2 rails would be deadheaded on the other end.

I was discussing this with my brother last night and after him telling me the assorted reasons why it wouldn’t work we started flipping through the current hot rod to look for other packaging ideas and found that all but one of the cars that they had pictures of actually had the rails fed that way (from the back and the front of the rails deadheaded).

So is there a point where this becomes unreliable? Other issues? The only thing that I could really think of would be the potential for vapor lock without fuel circulating through the system, but that can’t be that big a deal since this is essentially the same plumbing scheme the current returnless systems use but worse, they don’t even have the bypass regulator at the end of the rails…

Alternatively, and this won’t look as nice/I really don’t want to do it, I could do the big loop (in the back of one of the rails, through a crossover in the front, and then out to the regulator on the back of the second one), a little more cluttered but at least all the connections will be in one place.

FWIW, the engine is a turbocharged SBC with a converted victor jr, 2 x 255lph pumps (I have a pump controller circuit but I might just stage them), Mallory 4305M regulator (aeromotive pissed me off one too many times), starting with some 77lb/hr injectors and the fuel rail stock I was planning on using has a 9/16” ID.

The_Raven

Which way is your regulator designed to work? Byapssing or dead head?

Myself I'll always build a bypassing system.

Deadheading is strictly for cost. No return line, less cost in installing that tube, on a street rod/hot rod/performance car this makes no sense. There are many OEM vehicles going with a dead head system.

Your best bet is to Y the fuel line, through the rails, back intothe regulator.

A looped system really doesn't lose much, over a Y-ed bypassing system, so that will probably be your best of both worlds right there.

You should be able make the Y-ed bypassing system look plaeasing as well.

If you could mount the reulator on the manifold beteen the rails somewhere, and nice fittings, etc, this would simplify the plumbing, and keep it looking pleasing.

Remember Function ALWAYS before form, beauty is in the eye of the beholder, so you may spend all this time concentrating on what the fuel system looks like and yet to other people it may not look as pleasing as what you see.
Myself, if all I see is form then it losses it's apeal, but if fuction was the first priority and it was does clean, well that's awesome.

3.8TransAM

I would run a conventional system as well.

Dead heading is for cost and variable pump flow like on all the new cars.(although I'm not quite sure how they claim its cheaper with more software and fuel pump modules to control the pump flow rate and etc)

They also spike the FP to like 80+psi on restarts to keep it from boiling in the rails :-) (yes im a tech and yes I have observed this on multiple cars)

I would prefer to keep everything as balanced as possible and maintain the traditional intake/return sides.

later
Jeremy

83 Crossfire TA

iTrader: (2)

Well, I hate to burst your bubble guys, but that has nothing to do with it. It was done to prevent tampering with emissions related items on the car, especially with most emissions tests going to a plug in diagnostic rather then an actual test.

I’d bet that after the initial design hassles it probably does end up cheaper by not costing as much in warranty and emissions repairs replacing bypass regulators and related systems, even though I’m sure that is not why it was done in the first place.

I believe the spike, but are you sure that that is the reason for it? Is it published anywhere in the factory service documentation? I wouldn’t be surprised if it was just a lag in the feedback from the pressure transducer during cranking an initial startup.

yea, well if it wasn’t so damned ugly I’d be right there with you, but because it is I’m looking for an alternate solution…

Z69

I can't verify anything Mark.
But I do plan on doing a setup as you describe.
The only potential problem I can see is boiling during heat soak with the pump(s) off.
But I've yet to see anyone say they have seen it happen or show the specs for gasoline to prove it's possible.
I'm leaning towards it not being possible at 43psi.

At your power level. You could potentially run into some loss of pressure at the last injectors in the rail. No idea at what level that will occur at with 9/16 rails.
You might want to look at some of the LS1's to see how much power they have made with the dead headed rails system.( At least some LS1's have a return line at the pump.)
An inline efi pump won't last long w/o fuel flow for cooling.
I have an LS truck fuel rail that came with the injectors I wanted.. All it has is one inlet and a crossover near the end of the rails. If the OEM can do it.....

Have you done a search on TM about that Mallory regulator.
A while back some people were having problems with one model of the Mallory regs. It was sufficient to make me look at spending more for the Aeromotive reg.
Apparently you've had similar with Aeromotive.

3.8TransAM

I'm still willing to bet it was done for less parts.

Unless the gov forces them to do something, they dont, unless it makes sense for them financially over thousands of car :-)

Yes, I am/was a Jaguar Tech with over 5+ years in the field yadda yadda.

Lot of the stuff(80+% ecm/pcm/tcm was same or closely related to ford) and they actually do spike the pressure on startup since it is much more prone to boiling off fuel in the line without the return line.
(dont forget about hot start and cold start emissions bs to deal with, we dont have to but the oem's do)

This was told to me by field tech reps and engineers in the good ole UK :-)

Its really freaky watching a FP guage spike to 80psi on start up than drop back down to like 34 at idle than say 55psi at medium throttle.

I have wanted to test it on a stocker LS1(returnless system obvioulsy) and see what happens but I havent had a car and a guage available yet. Someone else chime in on this?

later
Jeremy

83 Crossfire TA

iTrader: (2)

Well the issue would be it boiling when it’s turned off and warm, as pressure drops in the rails… OTOH, if that does end up happening I don’t know how a pressure spike at start up would fix that unless they’re just trying to force the vapor out faster, and I would actually think that within reason this could make for an easier start up…

Huh, didn’t think of looking over there… good idea.

OK, people keep saying stuff like that and I don’t get it. There still will be flow just like there normally would, just not through the rails.

No I haven’t but I suspect that I know the deal. A while back when some of the required gas additive packages were changed by law amost all the fuel system companies had issues, Mallory and Aeromotive included. Mallory went “that sucks, this new stuff dissolves some of our parts” and replaced them for free. Aeromotive bull****ted their customers with “you ran alcohol through a part that wasn’t designed to deal with alcohol and ****ed it up. We can fix it for you for $xxx.” Between that, the Mallory being a better configuration for what I wanted and it coming with fittings for cheaper I chose the Mallory. The only issue with it is the thing is freaking huge..

I’ll believe the fewer parts, and the PWM circuit that they use to control it is probably cheaper then the hard parts it replaces, but I’m about 90% certain that it had to do with OBD and emissions standards. Hell, it would be a weird thing for most cars to go to that kind of system across the board in a matter of a year or two otherwise, wouldn’t it?

See, that’s the part that I don’t buy about the whole thing… I don’t see how they could predict how much boiled off in the rails and adjust for it during start up, so I have a hard time believing that it boiling really is a big issue IRL. I’m not doubting you or what you’ve been told, but the conclusions seem illogical.

yea, but that pretty much happens on a normal setup, even the pressure spike at start up to a lesser degree…

That would be interesting… If I remember tomorrow (later today) I’ll ask a guy that I know that has done a few LS1 swaps in the last couple of months if he knows…

jwscab

I think there is some confusion about how you are referring to dead-heading, thats why you keep getting the comments regarding how bad it is. The fuel supplies 'dead end' at the front of the rails.

I highly doubt it matters if you place the regulator as the first item in the chain. You're oversizing your rails (good idea), and as long as the two ports you feed to each rail are symmetrical, and close in length, you would have no problems. I could see something happening slightly funny at high flow where one line might feed more fuel than the other if its got less restriction.

If I was building a system from scratch, I would build exactly like you were saying: A high pressure feed to the regulator input, a high pressure feed to the back of each rail, with the front ends capped, and a single return off of the regulator back to the tank.

I have a zz502 lower manifold and fuel rail, and all 8 injectors are fed from the same rail,(neat, the injectors are placed on the inboard of the ports in the lifter valley, not outboard) with a single 3/8" line feeding into the center of it. The feed and return are both back by the distributor, and the regulator is the first device in the high pressure feed.

as for vapor lock and fuel boiling off, remember, the system is under pressure, and you have 8 'leaks' at idle, so other than maybe a slightly long crank time now and then, vapor will be shot right out of the injectors. I might be inclined to place the regulator on the fire wall, and try to make it slightly higher than the fuel rails, but that probably doesn't even matter.

mhaskell

I ran my vette a very simple way.

255 in tank to -6 fuel filter

from the filter to the rear of the pass fuel rail

-6 line from front of pass rail to front of drivers rail

aeromotive reg mounted to rear of drivers rail

output of reg to tank


Flows great and keeps the fuel nice and cool, havent had any problems with my 48lb injectors.