Fuel management with the Stillen Supercharger kit and Turbo's

[michaelnyden]

I know that if I get the Walbro 255, I have to get a adjustable FPR, but if I get the 190, I won't...how much higher flow is the 190 over our stock pump?

but if I am getting 370cc injectors, I will need an adjustable FPR anyway wouldn't I??? so might as well go for the 255? remember, I am planning on running a peak of 11psi of boost....

[Stephen Max]

I put this graph together using published fuel delivery data for Walbro fuel pumps:



The way to read it is to first look at the top axis and find the horsepower level you want to achieve at the crank. Go down to the purple line that best represents the brake specific fuel consumption your engine produces. From there go to the left axis to find what fuel delivery rate you need to achieve the desired power level. Then go to the green curve to find what fuel pressure level you need to stay below in order for the 190 lph pump to deliver the required amount of fuel.

In your case, let's assume you want at least 350 hp at the crank, and your bsfc is .6 (just to be conservative). Go down from the 350 hp hash mark on the top axis to the purple line representing fuel required at .6 bsfc. From the left axis we can see that the flow required corresponding to 350 hp at .6 bsfc is about 35 gallons per hour. Now go to the green 190 lph line and find that if your fuel pressure is less than about 50 psi, your 190 lph pump will deliver 35 gph.

Notice that your fuel pressure at 11 psi of boost is going to be at least 54 psi using a 1:1 oem rise rate. So the 190 lph pump may not be enough.

If your bsfc is .55 instead of.6 then your fuel requirement for 350 hp is less (about 32 gph), and your fuel pressure limit is raised to 60 psi, but you're still cutting it kind of close. Better to go to the 255 lph pump.

[IceY2K1]

I know this has been said a million time before, but what is the difference from the GSS341 and GSS342?

BTW, tons of these are on ebay for $82ish.

[michaelnyden]

what is the difference between the HP and the non-HP 255LP? I know what it stands for (high pressure), but what is the difference?

[1MAX2NV]

At higher pressure, it can sustain the flow rate (gph). While the non-hp, it will drop off very quickly.

[Stephen Max]

I wrote a little explanation of how the Stillen SC kit provides sufficient fuel during boosted operation. Maybe this will help answer some questions of people who are new to boosting.

As far as the stock fuel system is concerned. The Maxima uses an air flow referenced system. The mass air flow sensor (mafs, or maf) sends a voltage signal to the ecu based on how much air is flowing through it into the engine. The ecu uses that information, along with engine rpm and O2 sensor voltage to determine how long injector pulses should be to achieve stoichiometric combustion. This is for cruising and light acceleration and is called closed loop mode. Closed loop refers to the feedback loop in which fuel metering by the injectors is adjusted based on whether the O2 sensors detect combustion that is either leaner or richer than stoichiometric.

If the throttle is opened beyond a certain amount, as sensed by the throttle position sensor, the ecu goes into a mode in which it ignores O2 sensor voltage altogether and uses only the maf signal and engine rpm. This is open loop mode. Injector pulse widths are determined by a lookup table for each combination of maf voltage and engine rpm. The values in the lookup table are based on engine testing and give about a 13:1 to 13.5:1 air fuel ratio for the stock engine at wide open throttle.

When you install the supercharger kit you are significantly increasing the air flowing into the engine. This is not a problem during cruising and light acceleration because the SC does not exceed the air flow beyond what the maf is able to measure. At wide open throttle, however, it is possible to exceed what the maf can measure. Also, for boosted operation we want an air fuel ratio that is lower than what is provided by the ecu as a deterrent to detonation. The method that the Stillen kit uses to provide sufficient fuel for the additional air is to provide extra fuel pressure based on manifold pressure. This is done with the fuel management unit (fmu), which boosts fuel pressure according to a ratio that is determined by the size of the disk inside it. It is possible to have a fuel pressure to boost pressure rate as low as 3:1 and as high as 12:1. The stock Stillen kit comes with an 6:1 disk in the fmu (it might actually be 8:1, I forgot which), meaning that the fmu raises fuel pressure 6 psi for every psi of positive manifold pressure. This is a fairly crude way to tune, but it is simple and effective. In most cases it results in an overly rich afr at mid range rpm which leans out to an acceptable afr at high rpm.

In order to supply the additional fuel, either the Vortech auxiliary inline pump should be used, or the stock intank pump should be replaced with the Walbro 255 lph pump. The stock pump can not deliver enough fuel at a sufficiently high pressure to provide a rich enough afr to prevent detonation.

[slimer]

this needs to be stickied.

if we are going to talk about fuel. I think that the 370cc injector "how to" needs to be writeen up as well, as well as some of the other fuel injector threads, such as the z32 maf, scotts redesigned fuel set up, a ss line how to, and maybe some of the fuel settings for the safc and emanage (like jaime's for instance)

just my .02
steve

[dadiesel]

So if I have the Stillen Kit with everything the same except a 3.25' pulley, then it's recommended to get the Walbro pump? If you get the pump, then do you still need the blue FMU disc that came with the kit?

[Stephen Max]

Originally Posted by dadiesel

So if I have the Stillen Kit with everything the same except a 3.25' pulley, then it's recommended to get the Walbro pump? If you get the pump, then do you still need the blue FMU disc that came with the kit?

You need more fuel than what the oem fuel pump can supply. You have two options. You can use the Vortech T-Rex auxiliary inline fuel pump (that comes with the Stillen kit) along with the oem intank pump, or you can replace the intank pump with a Walbro 255 lph pump. If you go with the Walbro pump you do not need the Vortech aux pump.

In either case, you still need the fmu to raise fuel pressure when you are boosting. The only thing that would change that is if you installed larger fuel injectors that could supply an adequate amount of fuel at oem fuel pressure.

[Oblongshapes]

Ok, before I start in a couple weeks, im going to relocate the battery and get a 255 walbro fuel pump. I was wondering if the stock FPR would still regulate the right amount of fuel with the 255 pump.

Also, once I boost with the SAFC, will it control my pressures, or do i still need to get a FMU on top of the electronic management system.

Im just curious if I need to get a (non-stock) FPR and/or a FMU.

Thanks a lot,
Jeff


This post was a good one and a common one. So I tossed it in here and gave my answer below... Bags

[Bags]

Originally Posted by Oblongshapes

Ok, before I start in a couple weeks, im going to relocate the battery and get a 255 walbro fuel pump. I was wondering if the stock FPR would still regulate the right amount of fuel with the 255 pump.

Also, once I boost with the SAFC, will it control my pressures, or do i still need to get a FMU on top of the electronic management system.

Im just curious if I need to get a (non-stock) FPR and/or a FMU.

Thanks a lot,
Jeff

What amount of boost are you going to run?

Your FP, with the walbro, will be ~46 PSI at WOT. Not enough fuel if your boosting more than 4 PSI, IMHO.

Again, if your using stock injectors and boosting more than 4 psi, the SAFC will only be able to correct so much. You may be able to do 5 psi with the SAFC safely. You can use ONLY an FMU, but that is a broad adjustment. See the thread below this one for more info

The SAFC CAN'T control fuel pressure. It changes the amount of air the MAF thinks it's seeing. See below thread for more info if needed.

You NEED an FMU or bigger injectors. You can keep your stock FPR and slap an FMU on there and boost 8 psi without any real problems.

[Bags]

I'm borrowing Stephen's post and changing it slightly for TURBO'S...

This applies to Turbos and Supercharged maxima's using a MAF refferenced fuel system. I just stuck it down here as well.

As far as the stock fuel system is concerned. The Maxima uses an air flow referenced system. The mass air flow sensor (mafs, or maf) sends a voltage signal to the ecu based on how much air is flowing through it into the engine. The ecu uses that information, along with engine rpm and O2 sensor voltage to determine how long injector pulses should be to achieve stoichiometric combustion. This is for cruising and light acceleration and is called closed loop mode. Closed loop refers to the feedback loop in which fuel metering by the injectors is adjusted based on whether the O2 sensors detect combustion that is either leaner or richer than stoichiometric.

If the throttle is opened beyond a certain amount, as sensed by the throttle position sensor, the ecu goes into a mode in which it ignores O2 sensor voltage altogether and uses only the maf signal and engine rpm. This is open loop mode. Injector pulse widths are determined by a lookup table for each combination of maf voltage and engine rpm. The values in the lookup table are based on engine testing and give about a 13:1 to 13.5:1 air fuel ratio for the stock engine at wide open throttle.....


Also, for boosted operation we want an air fuel ratio that is lower than what is provided by the ecu as a deterrent to detonation. The "standard" varies from 11:1 - 12.5:1. It really depends on who you talk to. If your tuning in the summer, you may want to aim for the 11:1, so when it gets cold, if you pick up a 1-2 psi, your fuel system has a little more room for error. If your tuning in the winter, I'd go with 12:1. These are MY choices, NOT the RULE.

The method that most of us use to provide more fuel is pressure based on manifold pressure. This is done with the fuel management unit (fmu), which boosts fuel pressure according to a ratio that is determined by the size of the disc (icy) inside it. It is possible to have a fuel pressure to boost pressure rate as low as 3:1 and as high as 12:1.

The size of the disc will be detremined by the amount of boost your running and the size of your injectors. This can be determined by either dyno tuning with a Wide Band o2 or "street" tuning with a wide band o2. For example if using a 6:1 disc in the fmu, meaning that the fmu raises fuel pressure 6 psi for every psi of positive manifold pressure.

This is a fairly crude way to tune, but it is simple and effective. In most cases it results in an overly rich afr at mid range rpm which leans out to an acceptable afr at high rpm. Using a SAFC or piggy back like e-manage, you can get a FLAT A/F ratio from 2500rpm-7200rpm.

In order to supply the additional fuel, either the Vortech auxiliary inline pump should be used, or the stock intank pump should be replaced with the Walbro 255 lph pump. The stock pump can not deliver enough fuel at a sufficiently high pressure to provide a rich enough afr to prevent detonation.THIS IS A MUST.

Again, credit goes to Stephenmax for putting this together, I just added a word here or there.

[basevoid]

If anyone out there could please tell me what I should be looking for as far fuel pressure with this setup.

3.125 pully, T-Rex Pump, Cartech FMU

I am curious if anyone has logged their Fuel Pressure at given RPM in Third Gear.

If I am in Third at 2500 RPM, and then go to WOT my pressure jumps from about 40 psi to 62 psi and then climbs to around 80 psi at 6200 Rpm's

I'm thinking that the center screw may be in too far, because it seems like I have less torque when I'm at WOT (open loop) than I do at 3/4 pedal in closed loop.
I will be purchasing a wideband O2 at some point in the future, all I have right now is a millivolt readout for my stock O2. Any info or suggestions would be appreicated, Thanks Much.

[brasso]

Im running the stock fuel pump and fmu that comes with the stillen kit, I have stock injectors and im running the 3.33 pulley and all I have done is some tunning on the dyno to get a rich air/fuel mixture (12.1 to 1) and I have had no fuel problems after 2 years.

[streetzlegend]

iv done some reading on here and wanted to verify something that i am confused about. I have walbro 255 high pressure pump, along with 370's and afpr and vafc2. for under 8 psi, do you guys think i will need an fmu? (this is for turbo)

[crazyred]

I posted this in the supercharged discusson but ill try here as well for some advice.

i just bought a '98 I30 with a stillen SC. The previous owner said he also had a walbro 255 installed. I have gone through my first tank of gas and noticed when the fuel light came on, less than a mile down the road, the car began to sputter and run out of gas. Lucky i was at an intersection with a gas station. When i filled the car up it only took 16.5 gallons on an 18.5 gallon tank. Does anyone know why this may have occurred? Is the walbro pump have a shorter fuel pickup that leaves 2 gallons in the tank? Is there anything i can do to correct this problem to eliminate the problem?

Crazyred

[GodFather]

Originally Posted by crazyred

I posted this in the supercharged discusson but ill try here as well for some advice.

i just bought a '98 I30 with a stillen SC. The previous owner said he also had a walbro 255 installed. I have gone through my first tank of gas and noticed when the fuel light came on, less than a mile down the road, the car began to sputter and run out of gas. Lucky i was at an intersection with a gas station. When i filled the car up it only took 16.5 gallons on an 18.5 gallon tank. Does anyone know why this may have occurred? Is the walbro pump have a shorter fuel pickup that leaves 2 gallons in the tank? Is there anything i can do to correct this problem to eliminate the problem?

Crazyred

Your fuel pump sits in a dust collector plastic housing about 9"x5"x1.5" dimensions. When the fuel level is low enough, your fuel pump sucks all the fuel out of that housing while the rest of the 2 gallons aren't high enough to seep into it, thus causing an out-of-gas sputter to kill your car. (Basically, 2 gallons of gasoline spread evenly at the bottom of the tank is less than 1" high, not even close enough to get into the fuel pump housing.) If you can jerk your car hard enough like a hulk can, you may manage to spill a little more gasoline into it, and be able to start the car again till it runs out. But that's not humanly possible; what we do is "pump the gas when it's pretty low".

-Peter-

[The Wizard]

Originally Posted by crazyred

I posted this in the supercharged discusson but ill try here as well for some advice.

i just bought a '98 I30 with a stillen SC. The previous owner said he also had a walbro 255 installed. I have gone through my first tank of gas and noticed when the fuel light came on, less than a mile down the road, the car began to sputter and run out of gas. Lucky i was at an intersection with a gas station. When i filled the car up it only took 16.5 gallons on an 18.5 gallon tank. Does anyone know why this may have occurred? Is the walbro pump have a shorter fuel pickup that leaves 2 gallons in the tank? Is there anything i can do to correct this problem to eliminate the problem?

Crazyred

Originally Posted by GodFather

Your fuel pump sits in a dust collector plastic housing about 9"x5"x1.5" dimensions. When the fuel level is low enough, your fuel pump sucks all the fuel out of that housing while the rest of the 2 gallons aren't high enough to seep into it, thus causing an out-of-gas sputter to kill your car. (Basically, 2 gallons of gasoline spread evenly at the bottom of the tank is less than 1" high, not even close enough to get into the fuel pump housing.) If you can jerk your car hard enough like a hulk can, you may manage to spill a little more gasoline into it, and be able to start the car again till it runs out. But that's not humanly possible; what we do is "pump the gas when it's pretty low".

-Peter-

Myself and Ptatohed came to realize that there's a remedy to this problem. The stock fuel pump has its strainer parallel to the bottom of the gas tank and is able to suck up pretty much all the gas in the tank. The strainer that comes with the Walbro points upward at about a 30 degree angle and is not capable of sucking as much gas up (when it gets below approximately 1/8th of a tank) as the stock strainer.

To fix the problem, take the stock fuel pump strainer and put it on the Walbro fuel pump. This has been tested and proven to work during the course of installing Mike's (VIP Maxima) supercharger. With this mod, you can now drive your car like normal and not worry about running out of gas/poor performance at 1/8th of a tank.

[95BLKMAX]

I want to add to this (since i think this would be the more correct Sticky for this, move if necessary).

RC injectors that you buy and do not include the pigtail connectors-

NAPA P/N 2-17427. They were ~$6 each

Just have to trim off the edge at the tip and they will sit flush and clean (wont snap in and lock into place, BUT there's no reason for them to come off unless you pull on them).