Fueling 101

[RobertFontaine]

Figured I should ask the questions in a separate thread...

Fuel Injectors... Fuel Pumps... Boost a Pumps... Inline Pumps...

So working backwards from a Horse Power goal and knowing what kind of fuel I'm using I should be able to spec out a required fuel system.

How does I do this? Can someone please learn me.

thx.

[E30Alpina]

OK so what are power goals and fuel? Most likely a 255 w/ 044 will be more than sufficient for you.

[Colby Colbs]

Dood, get some books and read... like everyone else. Your posts are getting old fast...
You don't make sence half the time. Go stack money so you can DO something!

[chikinhed]

If you are sub 500 whp a Walbro 255 is all you need.

Sent from my GTX3582R

[MikeE36]

Figured I should ask the questions in a separate thread...

Fuel Injectors... Fuel Pumps... Boost a Pumps... Inline Pumps...

So working backwards from a Horse Power goal and knowing what kind of fuel I'm using I should be able to spec out a required fuel system.

How does I do this? Can someone please learn me.

thx.

There are no complex calculations around here, just rule of thumb.

Stock fuel hard lines under the car are good to at least 750 whp
Stock fuel pump (M3) good to around 400 whp
42# injectors up to a safe 450 whp (gasoline)
60# injectors up to a safe 600 whp (gasoline)
80# injectors up to a safe 800 whp (gasoline)

Walbro 255 good to a safe 550 whp (gasoline)
Aero 340 good to a safe 600-650 whp (gasoline)
Walbro 400 good to a safe 700 whp (gasoline)

Stock FPR good to 600+ whp (unknown - or at least I don't personally know. I use stock.)

Boost a Pump just cranks up your fuel pump voltage, allowing it to flow more at a given pressure. It will reduce the life of the pump, but it may be an acceptable amount that the lifespan change isn't that important (fuel pumps are relatively cheap for the most part over a few years in super high HP apps)

Inline pumps are only as good as the weakest link, and are often used when using a fuel cell, or swirl pot tank to pump to the fuel rail.

Most stock hardline setups and stock fuel tank setups (99.9% of bimmerforums) will use regular in-tank pumps and no additional inline pumps, so the above rule-of-thumbs for safe horsepower limits on a given pump are valid. Can they make more? Sure, but running any component at it's absolute max for an extended period of time will reduce it's lifespan significantly and it's more of a per-system basis as to how much fuel it takes to make X horsepower, so the exact limits are setup-specific and only testing for yourself will find them.

What else do you want to know?

-Mike

[wazzu70]

Mike excellent reply!

I think this was a pretty legit question. The general rules Mike went through should answer most questions.

Its nice to know at what point you need to go to an inline pump, ect.

[RobertFontaine]

Thank you mike,

I'm seeing some guys switching to the Walbro 400lph as they are going up over 500HP and today I noted that ICS going with a 250lph + inline Bosch + msd boost a pump for HP up in the stratosphere.

I'm extremely tempted to roll my own turbo and install my own EFI this coming fall/winter. Yes I recognize that it will cost me more, take me more time, incur significant rework and the results will be less than simply giving someone skilled with a proven product my money BUT this is my hobby and I find the whole thing fascinating.

Back to fueling questions.

Fuel injectors - A bosch 42# (440cc)injector can flow 42 pounds of fuel per hour at 43.5 psi (3 bar).

Does increasing the Fuel Pump's capacity from 250lph to 400lph create the ability to run the fuel system at more than 43.5 psi and effectively raise the injector's capacity to spray fuel into the system and if so how much wiggle room is there to run injectors at or over their max rated flow? Why is this a stupid idea when tuning an existing system?

[MikeE36]

Thank you mike,

I'm seeing some guys switching to the Walbro 400lph as they are going up over 500HP and today I noted that ICS going with a 250lph + inline Bosch + msd boost a pump for HP up in the stratosphere.

I'm extremely tempted to roll my own turbo and install my own EFI this coming fall/winter. Yes I recognize that it will cost me more, take me more time, incur significant rework and the results will be less than simply giving someone skilled with a proven product my money BUT this is my hobby and I find the whole thing fascinating.

Back to fueling questions.

Fuel injectors - A bosch 42# (440cc)injector can flow 42 pounds of fuel per hour at 43.5 psi (3 bar).

Does increasing the Fuel Pump's capacity from 250lph to 400lph create the ability to run the fuel system at more than 43.5 psi and effectively raise the injector's capacity to spray fuel into the system and if so how much wiggle room is there to run injectors at or over their max rated flow? Why is this a stupid idea when tuning an existing system?

When using a stock DME/ECU, the car is designed to run a 3.5 bar base fuel pressure across the injector. 3.5 bar in the fuel rail, "0" bar in the intake manifold, thus a pressure differential of 3.5 bar across the injector.

When you boost a car, the fuel pressure rises in a 1:1 ratio with boost. Ex. 10 psi boost + 3.5 bar base (51 psi) = 61 psi fuel pressure in the rail.

Based on this pressure differential across the injector, a certain injector pulsewidth (length of time the injector is open per pulse) correlates exactly to a specific amount of fuel supplied given the pressure is what the ECU expects (3.5 bar across the injector always).

If you change the fuel pressure, you will throw off a lot of the ECU's logic in the fuel mapping and mess up the tune. If using a standalone ECU, it may be less of an issue but I have no experience there.

The fuel pressure regulator is vacuum operated, and thus changes fuel pressure in a 1:1 ratio with boost. This is part of the problem of fuel pumps not providing enough flow at high boost levels. They do great at 50 psi fuel pressure (-1 psi on boost gauge) , but not so much flow at 80 psi. (29 psi on boost gauge)

Hope that rambling makes sense,

And yes, if you increase the fuel pressure and the fuel pump can keep up enough flow, an injector will flow more. Most injectors are rated 3 bar fuel pressure base, but our E36s run 3.5 bar, so a 42# injector is actually "larger" at the 3.5 bar base that we run. Same with 60 lb/hr, 80 lb/hr, etc.


Mike

[Fender13Bender]

One addition, 325s 328s and M3s use the same stock fuel pump. Not sure about 323s or 318s.

My fuel system is 100 percent stock except for 42lb Injectors and has lasted over 3 years and trapped 118mph in the 1/4 mile at 22psi on a SPA7000.

I would venture to say half the people on this forum don't even need to touch the fuel system at all.

Now, can anyone provide links for walbro 400 pumps and the like?

[e30kid89]

Good infomation here in this thread.

One small question I thought I'd ask since it's kinda on topic and I don't have to make a new thread..Will there be the dreaded "overpowered stock fpr @ idle issue" with the Aeromotive 340 or walbro 400? Kinda eyeing those pumps for a bit of extra headroom on my setup.

Also one thing that wasn't fully mentioned I thought I'd throw in is no matter what choice of pump you choose I would highly suggest (can probably get away with it sub 400whp) is wiring the fuel pump 12v+ directly to the battery so you avoid voltage drops via the stock wimpy wiring and guarantee full juice to the pump! Made a world of a difference for me once I had done this.

[RobertFontaine]

When using a stock DME/ECU, the car is designed to run a 3.5 bar base fuel pressure across the injector. 3.5 bar in the fuel rail, "0" bar in the intake manifold, thus a pressure differential of 3.5 bar across the injector.

When you boost a car, the fuel pressure rises in a 1:1 ratio with boost. Ex. 10 psi boost + 3.5 bar base (51 psi) = 61 psi fuel pressure in the rail.

Based on this pressure differential across the injector, a certain injector pulsewidth (length of time the injector is open per pulse) correlates exactly to a specific amount of fuel supplied given the pressure is what the ECU expects (3.5 bar across the injector always).

If you change the fuel pressure, you will throw off a lot of the ECU's logic in the fuel mapping and mess up the tune. If using a standalone ECU, it may be less of an issue but I have no experience there.

The fuel pressure regulator is vacuum operated, and thus changes fuel pressure in a 1:1 ratio with boost. This is part of the problem of fuel pumps not providing enough flow at high boost levels. They do great at 50 psi fuel pressure (-1 psi on boost gauge) , but not so much flow at 80 psi. (29 psi on boost gauge)

Hope that rambling makes sense,

And yes, if you increase the fuel pressure and the fuel pump can keep up enough flow, an injector will flow more. Most injectors are rated 3 bar fuel pressure base, but our E36s run 3.5 bar, so a 42# injector is actually "larger" at the 3.5 bar base that we run. Same with 60 lb/hr, 80 lb/hr, etc.


Mike

I think so but... Let me say it a different way to see..

In terms of capacity the pieces of the system are not fine grained. The system requires BOTH a specific pressure and a specific flow to work correctly. While BOTH are related they have different regulators and measuring systems.

If I have the capability to change the fuel map via some magic technique (stand alone, magic eight ball, etc)

then

Total flow capacity of the system would essentially be based on my HP target.

If I decided that I wanted to run 15 pounds of boost for no obvious reason ( and whatever that might mean in terms of CFM of air). I need to be able to flow more than 15 + 51 or 66 pounds of fuel per hour through the injector for the FPR to work properly. Let's say 66/.8 = ~82.5# injectors.

The actual squirting of fuel however would be based on the fuel maps and these would be magically adjusted (maf/map/02 sensor/secret sauce) based on the cubic feet per minute of air that I am flowing into the cylinder at a specific pressure (15 pounds in this example) at a point in time.

.... Looks like that's not right..

The 82.5 pounds is the pressure capacity required to sustain 3.5 bar in the fuel rail at whatever flow rate is required to support the horsepower at 15 pounds of boost.

The pulsewidth has to be adequate to get enough fuel into the cylinder to support the horsepower target.

The fuel flow at 3.5 bar has to be adequate to service the injectors.

[wazzu70]

I think so but... Let me say it a different way to see..

In terms of capacity the pieces of the system are not fine grained. The system requires BOTH a specific pressure and a specific flow to work correctly. While BOTH are related they have different regulators and measuring systems.

If I have the capability to change the fuel map via some magic technique (stand alone, magic eight ball, etc)

then

Total flow capacity of the system would essentially be based on my HP target.

If I decided that I wanted to run 15 pounds of boost for no obvious reason ( and whatever that might mean in terms of CFM of air). I need to be able to flow more than 15 + 51 or 66 pounds of fuel per hour through the injector for the FPR to work properly. Let's say 66/.8 = ~82.5# injectors.

The actual squirting of fuel however would be based on the fuel maps and these would be magically adjusted (maf/map/02 sensor/secret sauce) based on the cubic feet per minute of air that I am flowing into the cylinder at a specific pressure (15 pounds in this example) at a point in time.

.... Looks like that's not right..

The 82.5 pounds is the pressure capacity required to sustain 3.5 bar in the fuel rail at whatever flow rate is required to support the horsepower at 15 pounds of boost.

The pulsewidth has to be adequate to get enough fuel into the cylinder to support the horsepower target.

The fuel flow at 3.5 bar has to be adequate to service the injectors.

Robert, it seems you are confusing the lb/hr of the injector with the psi in the fuel rail. Remember the slang for pressure is "pounds" and is pounds per square inch. An injector @51psi will flow X number of pounds of fuel through it per hour. The pressure and the amount of fuel are two different things.

If your fuel pressure regulator is set to 51psi (the pressure of fuel inside the rail), this maintains 51psi of pressure ACROSS the injector. If the pressure in your intake increases 10psi that pressure fitting on your intake that goes to the regulator increases the pressure by the same amount. If the intake pressure rises 10psi and the fuel rail pressure rises 10psi to match, you still only have 51psi across the injectors so they flow the same amount if your intake is in vacuum or boost since the fuel rail pressure moves to match what the engine sees.

Maybe you understood that and I just misunderstood what you were getting at.


Now, onto the original question. You can raise the fuel pressure regulator to say 72psi (5bar) to force more fuel through the injector in the timespan it is open as controlled by the ECU (assuming you leave the tune alone). This is not really the best approach as raising the fuel pressure too high will not allow the injector to close or will delay the closing of the injector. Think of it as putting your finger over the garden hose when you barely turn it on versus full blast.....you get what I'm saying?

On the other hand...nice quality injectors like EV14s have much better atomisation at higher rail pressures. You can set your pressure at say 72psi and the injectors will love it since they are more designed to handle more modern pressure levels in fuel rails (HPF did a video showing the effects of different fuel pressures on atomisation). In this case you would have to tune the ECU to correlate with the ACTUAL flow rate since the injectors are rated at a 51psi rail pressure.

If you look at the different charts for a popular high quality injector like ID1000s you will see how the rail pressure impacts the actual amount of fuel dispensed. Just look at the corrected flow graphs at each pressure.

http://www.injectordynamics.com/ID1000.html


FWIW it killed me to write this up with Imperial units. No wonder the rest of the world dumped them

[bmmrr]

Robert, it seems you are confusing the lb/hr of the injector with the psi in the fuel rail. Remember the slang for pressure is "pounds" and is pounds per square inch. An injector @51psi will flow X number of pounds of fuel through it per hour. The pressure and the amount of fuel are two different things.

If your fuel pressure regulator is set to 51psi (the pressure of fuel inside the rail), this maintains 51psi of pressure ACROSS the injector. If the pressure in your intake increases 10psi that pressure fitting on your intake that goes to the regulator increases the pressure by the same amount. If the intake pressure rises 10psi and the fuel rail pressure rises 10psi to match, you still only have 51psi across the injectors so they flow the same amount if your intake is in vacuum or boost since the fuel rail pressure moves to match what the engine sees.

Maybe you understood that and I just misunderstood what you were getting at.


Now, onto the original question. You can raise the fuel pressure regulator to say 72psi (5bar) to force more fuel through the injector in the timespan it is open as controlled by the ECU (assuming you leave the tune alone). This is not really the best approach as raising the fuel pressure too high will not allow the injector to close or will delay the closing of the injector. Think of it as putting your finger over the garden hose when you barely turn it on versus full blast.....you get what I'm saying?

On the other hand...nice quality injectors like EV14s have much better atomisation at higher rail pressures. You can set your pressure at say 72psi and the injectors will love it since they are more designed to handle more modern pressure levels in fuel rails (HPF did a video showing the effects of different fuel pressures on atomisation). In this case you would have to tune the ECU to correlate with the ACTUAL flow rate since the injectors are rated at a 51psi rail pressure.

If you look at the different charts for a popular high quality injector like ID1000s you will see how the rail pressure impacts the actual amount of fuel dispensed. Just look at the corrected flow graphs at each pressure.

http://www.injectordynamics.com/ID1000.html


FWIW it killed me to write this up with Imperial units. No wonder the rest of the world dumped them

so is it belove correct?

51 psi base + 15 psi (1 bar turbo boost) = 66psi fuel pressure;

@66 psi fuel pressure;

walbro 255 and 42 lb injectors make 400whp @%100 duty (For example)
walbro 400 and 42lb injectors make 500 whp @ %100 duty (For example)


I mean same pressure and same injectors but walbro 400 flow more so make more power, is it correct?

[cragg56]

On the topic of FPR. I think I have seen some people switch from an OBDI fuel rail to an OBDII fuel rail so that they can run an aftermarket FPR without having to use a block off plate in the OBDI rail.

I can't find the thread that described this, but I was wondering if there is anything special needed to bolt the OBDII rail to an OBDI manifold, if I am installing it in an OBDI car. Understand the lines run differently, but I am just talking about attaching the rail to the intake manifold.

[MikeE36]

so is it belove correct?

51 psi base + 15 psi (1 bar turbo boost) = 66psi fuel pressure;

@66 psi fuel pressure;

walbro 255 and 42 lb injectors make 400whp @%100 duty (For example)
walbro 400 and 42lb injectors make 500 whp @ %100 duty (For example)


I mean same pressure and same injectors but walbro 400 flow more so make more power, is it correct?

Let's assume for the moment that we are NOT going to overly complicate things for any fuel system shooting for less than 800whp by changing the fuel pressure.

Assuming 3.5 bar across the injector, 42# injectors will hit 100% duty cycle and max out between 450-500 whp. Going to a larger fuel pump will not increase this limit.

-Mike

[wazzu70]

The higher flowing pump only makes more power if the smaller pump could not meet the fuel demand.

Any excess fuel sent to the rail above what is needed to maintain the pressure differential set by the regulator is sent back to the fuel tank through the return line.

You know you need a higher flowing pump when the pressure across the injectors starts dropping.

The boost a pump sends more juice to the fuel pump at higher RPM to make the pump output more than it does regularly to maintain fuel pressure in the rail.