Fuel System Upgrade Info - Something Doesn't Add Up

[habitatguy187]

According to this article from vfaq, the stock fuel filter only flows 1.9lpm @60psi fuel pressure, which is only 114lph. When they turned the fuel pressure up to 75psi the actual flow only increased .1 lpm. The article also claims that the stock fuel filter can only flow a max of 2lpm, or 120lph.

Now I have a hard time believing this info since people have documented lower IDCs when upgrading to a larger fuel pump like a 190 or a 255. Also if this info is true then a 1g running 23psi is pushing as much fuel as possible through the filter, and an increase of 5 or 6psi would seem to knock like crazy, and I've read of many running 30psi + on a stock fuel filter.

Discuss

 

[ramsack]

it would really depend on the filter (oem or parts store) being used but if i remember correctly the holes in the fittings on the filter are damn small and anyone staying with a stocker is just gambling that it will flow enough. it might be that he meant with stock lines it barely flows, because i know for a fact that the banjo hole is pretty puny on the bolt, so maybe AN fittings would make the stock filter flow more. i would just go with a fuelab filter or something aftermarket that you can replace the filter element. it will be cheaper in the long run.

 

[habitatguy187]

I was also thinking the same thing, but then in the article he says the "fuel filter is a low-flow design, 2lpm" He also lists the banjo bolt and fuel rail feed hole as restrictions, but the filter itself is said to only flow a max of 2lpm.

I was thinking about that and if that's the case then everyone with a stock fuel filter would need nothing bigger than a 150lph fuel pump, or maybe just a re-wire on the stock fuel pump. This obviously isn't the case so I'm wondering how a 255lph pump could possibly flow more fuel than a 190lph pump when the fuel filter can flow no more than 120lph (2lpm*60mins)????

 

[ramsack]

you are correct that you can't flow more than a restriction allows...unless you up the pressure...which is what a 255 would do. people also incorrectly assume that pressure at their fpr = more volume of fuel available for the injectors.

from what i've seen on mitsubishis their oem fuel system is pathetic. especially the 3000gt system. most mitsus have fpr overrun when you put a larger flowing pump and lines on, and something like the 3000gt could have been cured with a larger feed line, a y fitting to split the fuel to 2 rails, and 2 fprs, instead of running through a rail, a fitting to go from one rail to the other, then through the other rail, the fpr and return.

it's best to just re-engineer from the ground up like stevetek did.

 

[habitatguy187]

you are correct that you can't flow more than a restriction allows...unless you up the pressure...which is what a 255 would do. people also incorrectly assume that pressure at their fpr = more volume of fuel available for the injectors.

But they upped the pressure to 75psi and only gained .1lpm flow. Like Steve said that's a 25% increase in pressure and only a 5% increase in flow. If that's true then anyone with a manual 1g running over 23ish psi on the stock fuel filter is going to detonate their car to hell. Now since there's lots of people on here, myself included, who have ran over 25psi on the stock filter it really has me curious as to how we haven't blown our motors up.

 

[ramsack]

yes, he increased the pressure on a stock pump, which if you upgrade lines, won't flow much more even with pressure increase. and yes i know of people running high boost and big turbos and not bothering with fuel lines or anything, and some of them i know personally, and have ended up with engines that are just scrap by the time they're done with the car. stuff like this is what attaches to certain engines or cars with them and makes false stereotypes that they are unreliable.

 

[donniekak]

I have a brand new stock filter on my car, with a -an fitting to a braided line to an aem rail. I keep a rock solid 12:1 afr at 26 psi to 8,000 rpm's. This is with rc 1000's, a single hotwired wally, and e85.

 

[habitatguy187]

yes, he increased the pressure on a stock pump,

I didn't think about that. So you're saying that the reason for such a low increase in flow was due to the stock fuel pump running out of steam, not the fuel lines/restrictions.


That makes sense, but even so if the stock filter can only flow 2lpm I don't see a way around that without changing out the filter. It seems that upping the fuel pressure with a bigger fuel pump would do nothing but bottleneck at the fuel filter, wouldn't you agree?

 

[tkelly27]

You're right, the numbers do not add up. Assuming you'd need 60psi across the filter to get 114l/hr plus the 37.5psi base pressure you're already at 100psi pump pressure by 2.5psi of boost.

Eclipse Fuel Pump Tech Tips

as you can see at 58 psi (at the pump) it's all the way down to 70l/hr. I doubt the pump even flows above 80psi, so this really can't be the case.

I'm not really sure how they tested it, but it would have been nice if they had put the aftermarket filter through the same test.

A 255, new stock filter, and stock feed/return line is a decent solution up to 500hp or so. It's been done many times over, and will continue to happen. If you need a new filter and are thinking you may want more power than that, or may want to run ethanol, a new filter is a really good idea, and bigger or double lines from the tank are also a really good idea.

 

[habitatguy187]

I have a brand new stock filter on my car, with a -an fitting to a braided line to an aem rail. I keep a rock solid 12:1 afr at 26 psi to 8,000 rpm's. This is with rc 1000's, a single hotwired wally, and e85.

Do you have a link to the -an fitting for the filter?

 

[ramsack]

there are so many factors to the stock system that can flow up to big hp numbers, but making a fuel system from scratch isn't that expensive and it's going to be most efficient. the only thing IMO that doesn't ever need to be upgraded unless you're going to like a tube-chassis car is the fuel rail. aem says their rail will flow for 1000hp, and it's 1/2". the stock rail is bigger than that. next step up would be the aeromotive rail (5/8") and then the FIC rail (11/16").

you can choose to skimp out on things in the fuel system just because some people have made big power on them, but don't expect it to last.

 

[habitatguy187]

^^^^ I didn't say a thing about piecing together a fuel system or even my own mods, just curios as to what this article says about the stock filter only flowing 2lpm. As I stated, I don't understand how that could be possible when someone like diambo4life has ran 10.5 using e85 with no fuel system upgrades besides twin pumps and injectors.

The article must be false unless there's something here that I'm missing, which is why I posted. If it's not false and it's true that the stock fuel filters max out at 2lpm then how in the world are people doing what they're doing with them?

 

[ramsack]

the article is crap. he tested shit with a stock pump! as i said before you don't need to upgrade lines and filter, but you will need way more pumping power to overcome the stock crap to make the same power, which is why that diambo dude needs 2 pumps. i would love to mount a fuel pressure sender at his pumps, and one at his fpr and see the pressure difference! he's probably also getting away with a stock fpr because of not upgrading anything else.

just because something is possible doesn't mean it's ideal.

 

[donniekak]

The most restrictive part of the stock fuel system is the banjo fitting coming out of the filter.

 

[ramsack]

where the tube goes through the plate that bolts to the tank is pretty much as small as the banjo bolt. there are 4 points that i'm aware of:

1. fuel pump assembly plate, where the tube runs through the plate.
2. fuel filter has 2 of them:
a. inlet inverted flare is pretty small
b. banjo bolt in the top
3. the fitting that goes into the rail to supply fuel to it.

i just think you gotta be whacky to use 2 high-flow pumps to force fuel through the stock line. if you upgrade the line, there is no need for 2 pumps until you actually exceed the rating for that pump, and not what a stock fuel feel system is giving you. the stock line from the tank to the filter is more restrictive that just that banjo bolt and feed to the rail. it has to travel like 12 feet through 5/16" tubing.

EDIT: what the stevetek article is trying to emphasize is that if you get rid of all the restrictions before the rail, the injector for cylinder 1 won't be starved. you may have the proper fuel pressure using a stock line and 2 pumps, but your engine isn't being fueled properly on high fuel usage. if you could put a wideband on each cylinder it would prove my point and stevetek's. he shows how to safely fuel an engine the right way.

 

[dsm-onster]

A diameter is only part of the equation for fluid restriction. The banjo bolt forces the fluid through the small hole WHILE making it turn 90-180*. Yes, a longer thin pipe is far more restictive than a short thin pipe, as well. So you're right, you have to look at length, not just pipe area. But you also have to look at pathways/bends. And the banjo bolt at the filter is full of fail.

 

[99gst_racer]

Do you have a link to the -an fitting for the filter?

You can use any Solex carb fitting (M12x1.25 thread).

Earls 991945
XRP 700903

Either one of those will thread into the top of the factory fuel filter and allow you to go -6 AN from there.

 

[habitatguy187]

As a side note it seems like putting a high flow fuel pump in such a bottle-necked system would really put a lot of strain on the fuel pump, is that correct?

 

[ramsack]

yes, and it doesn't fuel the injectors evenly. you may have enough pressure, but that doesn't mean the flow is there for the last injector in the rail. it's been noted by stevetek for dsms and other people for other car communities that if you put a big pump on a car and have restrictions in the fuel system that you will not be fueling the injectors themselves correctly. you may run high hp numbers and good 1/4 times, and your afr may show correct, but this a product of all cylinders. until someone puts a wideband on each cylinder and log each one, i will sound like an asshole.

 

[pneumo]

There's 2 things wrong with the Stevetech article: like you said, the filter can flow more than 2lph if there's a good pump behind it.

Second, the injectors are fed evenly regardless of fuel pressure. There is no mechanism present in the fuel rail that limits flow or pressure to an individual injector while allowing greater flow/pressure to another. The stock fuel rail is a large open tube, if pressure drops then it will drop evenly in the whole rail.

The only good thing about the Stevetech article is that it shows how to build and install high flow fuel lines.

 

[donniekak]

I don't see how the stock filter could only flow 2 liters per hour, maxxed out stock injectors flow almost 2 liters per minute. I have maxxed out 1000's on the stock filter which is 4 liters per minute. So even if you mean to say liters per minute, over liters per hour, i have flowed double.

 

[dsm-onster]

There's 2 things wrong with the Stevetech article: like you said, the filter can flow more than 2lph if there's a good pump behind it.

Second, the injectors are fed evenly regardless of fuel pressure. There is no mechanism present in the fuel rail that limits flow or pressure to an individual injector while allowing greater flow/pressure to another. The stock fuel rail is a large open tube, if pressure drops then it will drop evenly in the whole rail.

The only good thing about the Stevetech article is that it shows how to build and install high flow fuel lines.

YES! pressure is the same, physical dimensions of the tube to the injectors is the same. Fluid tends to flow from high pressure to low pressure, so pressure across the rail remains constant. I've installed fuel pressure gauges on either end of the rail on the same setup and saw that. ll one cau say sithat there is more resistance by the time you get to the end of the rail. Which yes is true length does affect flow. But length has a very, very minor effect on viscous resistance vs. tube radius.

In all, I think the original mitsu engineers would have forseen a problem. Cylinder #1 gets the most air, per flow bench testing. So if injector one spits out the least fuel, you're in for real trouble quickly. One overboost episode with a stock 14b could crack a piston.

 

[rarest_90_DsM]

Trick Flow Specialties TFS-23000 - Trick Flow® TFX? Inline Fuel Filters - Overview - SummitRacing.com Solution thats what i run on my car and its pretty reasonably priced to.

 

[99gst_racer]

Trick Flow Specialties TFS-23000 - Trick Flow® TFX? Inline Fuel Filters - Overview - SummitRacing.com Solution thats what i run on my car and its pretty reasonably priced to.

That one is only 40 Microns, though. I personally wouldn't want to run anything more corse than a 10 micron on an EFI engine.

Dan and I have been rocking this fuel filter for a few years now, and it's been great: http://www.allstarperformance.com/product.htm?prod=320&part=ALL40216&add=no

 

[habitatguy187]

So I was changing out my fuel injectors today and while I had the rail off I decided to take the top hose from the fuel filter off and examine the banjo bolt, since last time I saw it I was a complete noob with 275hp goals .

While looking at it I had a very simple idea that would help it flow more, but I've never heard anyone mention anything about it. Basically all I did was line up the holes in the banjo bolt to the inlet of the fuel feed line so that the fuel wouldn't hit the wall of the banjo bolt first thing and be forced to find a way out. Very simple and looks like this (on the car and bolted down)

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It took just a minute to figure out where the fuel line needed to be so that the threads would end up in the right place when tightened all the way down. Such an easy "mod" that I don't doubt one bit will increase fuel flow.