When the secondary injectors kick on at about 5-7 psi, what keeps the fuel pressure from dropping? If the fuel pressure does drop when the secondary injectors kick on, will this induce detonation?

I have been having a very deep technical discussion with one of my friends, and he says the risk is there with the corbin setup. He says I should keep the stock system totally isolated, and run another walbro, and fuel line to the secondary fuel rail itself. I told him there won't be a problem with this happening because of the amount of fuel I'll be running.

By the way I am running 235 (stock) and 440 (secondary).

Let me know your feedback guys!!! I need this information ASAP.

Bump

That won't be an issue. Your fuel pressure will acctually go up when they kick in because it is a 1:1 reg so it will raise with boost. If it was a non rising reg I could see that being a problem, but look at the fuel pressure you can get out of the systems that come with the kits, 110psi. Now when running 8 injects your going to drop the pressure needed to run the car, but the system would still be able to provide 110 psi of fuel just like before. Don't worry about it you'll be fine.

Anyone else?

You bring up a good question and something that I hadn't thought about before. I could see you having a momentary drop in pressure when the secondary injectors kick in simply b/c of the extra volume of fuel that you'll dumping instantaneously. The fuel pump should be able to catch up quickly, but not sure how that all will work. One thing Kirby didn't mention though is that you will have to add the volume requirements for each injector together and then check your pressure and make sure your pump(s) can supply that volume of fuel at that pressure. They should be adequate, but just something else to check. True, the walbro can supply fuel at 110psi, but the volume is fairly low.

Clarifications:

The recommended fuel pressure regulator is 1:1. It increases fuel pressure to match intake manifold pressure. So there is as much fuel available at 0 psi as 18 psi.

The secondaries should actually kick in before 1 psi and continue to provide more fuel as boost rises. So the demands are progressive (not all or nothing). The FPR and pump can adjust fast enough to changing demands.

You don't need to run a completely separate fuel system for the secondary rail. Do factory V8 cars run dual fuel pumps, regulators, and lines? The ones I've seen run 2 rails in series with one pump, regulator, and lines (like my 8 injector setup).

In a 4 injector application, you don't run a separate fuel system for each injector. Do you worry about the #1 injector sucking fuel away from the #2 injector? Similar situation to the 8 injector setup. There is enough volume in the lines and rails to supply all of the injectors.

Check out the Walbro graph:



It can supply a shitload of fuel at 30-60 psi (8 injector territory). Thats 3,780 cc/min of fuel at 40 psi.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

Thanks Corbin.... Your the best!

there is no pressure drop when the second injectors kick in. This is why you run a 1:1 fpr with this setup.

The fpr increases fuel pressure with boost. as boost increase, fuel pressure increases.

The fpr works by restricting the return line to the tank, thus increasing pressure at the rails (same volume, but now more fuel in the same volume of space). This is independent of how many injectors are firing.

to increase fuel pressure, even when more injectors begin firing, that restriction is just increased, thus maintaining or increasing fuel pressure as needed.

Yep, Corbin and others are right. You basically don't need to build seperate systems for each rail. If you build it like Corbin's writeup withe a 1:1 regulator, it should be a great system.

I will add to this conversation the ONE thing that you may want to concern yourself with. This issue affects both 4 or 8 injector systems, but may be of more concern to the 8 injector users. I've brought this point up before, and really the only reason I bring it up now is because of the size of youre rear injectors.

Read this http://www.stevetek.com/R-FuelSys.html . It's a study on the fuel system for our car. Though the pump can support an enourmous amount of flow at the pressures that we're dealing with - the filter and several other points throughout the fuel delevery system are only adequite up to approximately 2 liters per minute. I know, the study was done on a 1g, but there's a 2g addendum http://www.stevetek.com/R-FuelSys2G.html . Basically, the non-turbo cars have the same lines/filter/banjo and a similarly small rail inlet. Take a close look. Because it is also used on our turbo brothers, the system is capable of delivering more than twice as much fuel as we need N/A...but not 3 times as much(even though the pump IS capable).

This is NOT something you have to worry about if you plan on keeping fuel usage under 450-500 cc/min per cylinder. But if you plan on maxing out those 440s on the rear then it's likely you'll have problems on the way - somewhere between 300 and 350 crank horsepower. I don't want to sound like chicken little here "The fuel level is falling! The fuel level is falling!", but the situation gets a little more dramatic when you convert to an 8 injector system. Why is this? Take a look at Steve's picture of a rail running dry after it passes the flow capability of the fuel delivery system.


The reason that folks with an 8 injector system should concern themselves with this particular issue moreso than the 4 injector people is because the secondary rail is mounted upside down - with the injectors sucking out of the top of the rail(turn that picture upside down). So once you go beyond the flow capability of the fuel delivery system - the secondary injectors will hit air ALOT sooner. Boom!

That's the ONLY problem I see with using the 8 injector system and it ONLY applies to folks gunning for high HP AND it doesn't have anything to do with the 8 injector system specifically. It has more to do with the fuel system delivery capabilities of our car along with the fact that we have to mount the rail somewhat upsidedown. It is the reason why I am upgrading my fuel delivery system(-6 AN fuel lines, high flow fuel filter, -8 AN rail tie) while I convert to 8 injectors.

But like I said, if you do it like Corbin laied it out, you can confidently tell your friend that it is a great system. Much better(in several respects) than the high rising rate systems like you get with the kits. I think the main reason as it pertains to your question is - The 1:1 fpr keeps the pressure differential between the rail an manifold at a constant. This makes predicting injector output in OR out of boost much easier. In boost, when you really need to get the right stuff, it enables constant output on the primaries(same fuel output at 1psi boost as there is at 30psi boost), as well as permitting consistant regulation on the secondaries(6ms pulsewidth at 1 psi boost will give you the same amount of fuel as 6ms pulswidth at 30 psi boost). It behaves much more like a "real"(oem) turbo fuel system as far as how the rail/manifold pressure is managed.


95 Eclipse RS : 5 speed
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html

I've read that site regarding the author's theories with fuel pressure differential across the rail and it possibly being lower on the FPR side.

I remember Bill Hahn refuting that very issue on DSMtalk IIRC as well. And it makes sense that the abovementioned theory has holes in it, especially if the fuel pumps that are being used are sufficient to meet the fuel delivery needs.

Rememeber, if this theory would indeed be prove itself true in an 8-injector sense(or any sense), you'd notice a discernible "blip" or drop in your fuel pressure as you boosted, during your transition to boost, or at high rpm boost. We have to remember, that because we've built our turbosystems, from the grass roots, so to speak, we're much more conscious of not only fuel ratios, and EGT's, but also their important relation to fuel pressure. Most 4g63 guys don't worry a whole lot about this, merely blindly depending on their stock FPR to "get the job done." (Their stock FPR does have issues with being overrun with high performance fuel pumps)

With the install of an 8 injector setup, and a 1:1 FPR, I think it's not only necessary, but prudent, when initially tuning, to monitor your fuel pressures just as you did before with a hgih pressure rising rate fuel system, and now with the implementation of this more innovative fuel system. With that, you should be able to discover whether or not, your fuel pump is keeping up with the fuel demands, with what I would describe as some sort of noticeable fluctuation in the fuel pressure. We should also remember that we're dealing with a pressurized environment within the fuel rails leading up to the FPR. Gravity is irrelevant. All of the space is and should be occupied with fuel. If it weren't, again, you'd notice a drop in fuel pressure, and you certainly wouldn't be maintaining any sort of fuel pressure over 30-40 psi. (At boost, I'm closer to 60 psi)

So again, I think that gentleman's website and theories in regards to lower fuel distribution closer to the FPR along the pressurized fuel line is misplaced, so long as your fuel pressure gauge indicates as much. With most all of us running Walbro 255's and performance inline fuel pumps (or both, like me), such concerns are most likely not well founded.

Corbin's analogy regarding V-8 performance cars running the "same" fuel system with similar fuel pumps makes more sense. Concerns regarding the "kicking in" or transition into the secondaries shouldn't be of any sigifigance, again, for any of us, from a practical standpoint. But to alleviate those worries, again, just monitor your fuel pressure gauge. :thumbsup

Thanks everyone!!! By the way, I am upgrading all the fuel line to 6AN lines, the Walbro 255 is already in the car.

So what does everyone think the HP capabilites of this system are? Take for instance my setup.

Star Turbo Kit t03/t04e
Built motor 8,6:1 compression
8-injector setup 235cc-440cc

running 25psi

For those of you running 8-Injector setup. Have you totally removed the original stck FPR? or did you still use it in some way?

Since I have the same setup, I've already calculated it to be enough for over 450 HP. Remember, 440 + 235 at its max output, is similar to have 4 - 675cc injectors. Is that enough? :+

That's some pretty good fuel/horsepower capability in terms of cost efficiency, when you consider the cost of a $250 injector controller versus a $1000 stand alone. All that, while maintaining your off-boost stock ecu control and mileage.:thumbsup

Addendum: most all of us run the Aeromotive 1:1 FPR (#13109 model IIRC). Listed on Corbin's website.

Yes I am going to run the Aeromtive 1:1 FPR as well. but what I need to know is, did you completely remove the stock FPR or is it still tied into the fuel system someway?

>Yes I am going to run the Aeromtive 1:1 FPR as well. but what
>I need to know is, did you completely remove the stock FPR or
>is it still tied into the fuel system someway?

No, it's been long gone since the turbosystem was first installed so long ago with a Cartech FPR. Similar to that setup, the Aeromotive totally replaces the stock FPR's function of controlling the stock idle fuel pressure. (and does a better job of it!)

>I've read that site regarding the author's theories with fuel
>pressure differential across the rail and it possibly being
>lower on the FPR side.
>
It is not a theory at all. It is an analysis of our fuel delivery sytem. The problem has more to do with flow than pressure. He measured the flow capabilities of the system overall, from the pump outlet through the lines, the filter, the banjo fitting on top of the filter, the through the inlet into the rail - how well the whole system flows.

>I remember Bill Hahn refuting that very issue on DSMtalk IIRC
>as well. And it makes sense that the abovementioned theory
>has holes in it, especially if the fuel pumps that are being
>used are sufficient to meet the fuel delivery needs.
>
The pump is only one part of the system - and that particular part has nothing to do with the test. These tests were done using a liquid flow bench from the pump outlet to the rail inlet. Look real close - the pump that's used is that of the flow bench. Regardless of what pump you use, the stock fuel delivery system(from the pump outlet to the rail inlet) flows 1.9lpm@60psi and 2.0lpm@75psi. The stock pump can't even flow that much at those pressures. The Walbro 255s can.

>Rememeber, if this theory would indeed be prove itself true in
>an 8-injector sense(or any sense), you'd notice a discernible
>"blip" or drop in your fuel pressure as you boosted, during
>your transition to boost,
No.

> or at high rpm boost.
Yeah, that's when you'd see the problem. The problem only happens when you demand more fuel from the rail than you can get into it(1.9lpm@60psi and 2.0lpm@75psi). At that particular point, if the fuel pressure gauge were mounted on the end of the rail(or on the fpr like we have it) you would see a drop in pressure. If it were mounted at the filter however, you may not see the drop in pressure.

> We have to
>remember, that because we've built our turbosystems, from the
>grass roots, so to speak, we're much more conscious of not
>only fuel ratios, and EGT's, but also their important relation
>to fuel pressure. Most 4g63 guys don't worry a whole lot
>about this, merely blindly depending on their stock FPR to
>"get the job done." (Their stock FPR does have issues with
>being overrun with high performance fuel pumps)
>
>With the install of an 8 injector setup, and a 1:1 FPR, I
>think it's not only necessary, but prudent, when initially
>tuning, to monitor your fuel pressures just as you did before
>with a hgih pressure rising rate fuel system, and now with the
>implementation of this more innovative fuel system. With
>that, you should be able to discover whether or not, your fuel
>pump is keeping up with the fuel demands, with what I would
>describe as some sort of noticeable fluctuation in the fuel
>pressure.
Absolutely

>We should also remember that we're dealing with a
>pressurized environment within the fuel rails leading up to
>the FPR. Gravity is irrelevant. All of the space is and
>should be occupied with fuel. If it weren't, again, you'd
>notice a drop in fuel pressure,
Yes it should be occupied with fuel. The whole point of the study is to demonstrate that if your injectors outflow the fuel coming into the rail then you will start to "drain" the rail. And yeah - I would imagine that initially it would show as a drop in fuel pressure, eventually creating a gap of air in the rail. The reason gravity is more important for the 8 injector system is because the secondary rail, the one that demands the most fuel, is upside down - so this air gap would be located on the top of the rail, where the injectors are demanding the fuel from.

>and you certainly wouldn't be
>maintaining any sort of fuel pressure over 30-40 psi. (At
>boost, I'm closer to 60 psi)
>
I have no idea what fuel pressure this problem would rear itself. It's not really a pressure issue - it depends more on how much fuel you're putting through the injectors. You'll start to see the problem when the injectors demand more than around 2.0lpm(500cc per minute - per cylinder).

>So again, I think that gentleman's website and theories in
>regards to lower fuel distribution closer to the FPR along the
>pressurized fuel line is misplaced, so long as your fuel
>pressure gauge indicates as much. With most all of us running
>Walbro 255's and performance inline fuel pumps (or both, like
>me), such concerns are most likely not well founded.
>
Again, it is not a theory. It is a liquid flow bench analysis of our fuel delivery sytem. In stock form our systems can flow about 2 liters worth of fuel from the tank into the rail - regardless of what pump you use. The problem isn't with the pump, it's with the lines. The filter is a low flow design - rated at 2lpm. The banjo fitting at the outlet of the filter is restrictive. The fitting at the inlet of the fuel rail is extremely small. No matter how big a pump you use - only so much will flow through a 5.5mm tube(rail inlet) at a particular pressure. Only so much will flow through the low-flow fuel filter and it's banjo bolt at a particular pressure. I think that out of every part of our system - the filter is probably the most restrictive

>Corbin's analogy regarding V-8 performance cars running the
>"same" fuel system with similar fuel pumps makes more sense.
>Concerns regarding the "kicking in" or transition into the
>secondaries shouldn't be of any sigifigance, again, for any of
>us, from a practical standpoint. But to alleviate those
>worries, again, just monitor your fuel pressure gauge.
Absolutely.


95 Eclipse RS : 5 speed
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html