Challenge Friendly Fuel Injection

I am currently working on a challenge car that will be using megasquirt. I have the computer, wiring, and such pretty much figured out. Where I am struggling is the fuel system.

1. Since I am running boost, should the fuel system be boost regulated? Where should I look for a proper regulator that is challenge friendly?

2. Is this a good fuel pump?

http://www.diyautotune.com/catalog/walbro-gsl392-255lph-fuel-pump-p-312.html

If this is not a reliable fuel pump, or there is a better option for the price, where is a good source for fuel pumps?

1. Is braided hose adequate for fuel injection, or should I be looking for a special type of hose?

2. I have come across a set of properly sized injectors, but they are low impedance. Is megasquirt 1 capable of running low impedance injectors?

Any help or additional suggestions would be greatly appreciated.

Walbros are good but the go to junkyard pump is off of a cis equipped vw. Good for 400whp as long as it works.

Ms can drive low imp with resistors no problem. For on board limiting you need a v3/3.57 or mods to a 2.2.

Regulator should be referenced to manifold pressure. Almost any stock regulator works. Some Vw and bmws have ones with hose ports.

Most folks say you have to use a manifold referenced regulator but I haven't found this to be the case.

For packaging purposes I used a GSXR fuel pump in my fiat with the internal regulator and no return line. It runs one pressure all the time. Pretty much everyone told me this was destined to fail and that I would need a boost referenced unit. It works great. There were no issues tuning it. I would do it again in a heartbeat.

You don't get much added fuel with even a 10psi pressure bump.

With standalone and fixed fuel pressure the only difference is that some numbers on the map will be higher or lower than if you had referenced.

A boost referenced regulator is a good tool for modifying a car with an OEM ECU but with standalone it is just an extra thing to buy.

From a tuning perspective the numbers "make sense" when the regulator is referenced. This is true for the vacuum range and boosted. If your ve table has limited range of adjustment it is more important.

The nice thing about walbros is they sell a bunch so they are easy to find used. Some Ford trucks have a beastly external fuel pump that flows plenty that could be an option as well.

More Questions

1. Where should the pump be located in relation to the fuel tank?

2. Is this cable adequate for a relay cable? I have read that some of the wires need to be beefier. http://www.amazon.com/SF-Cable-Serial-Straight-Extension/dp/B0016S5DGQ

3. Does it matter what fuel type a fuel pump uses? I guess what I'm wondering is, if I take a fuel pump off like a ford diesel truck, can I use it on gasoline?

4. How do you calculate what gallon per minute fuel pump is required for a certain horse power level?

Ditchdigger wrote: Most folks say you have to use a manifold referenced regulator but I haven't found this to be the case. For packaging purposes I used a GSXR fuel pump in my fiat with the internal regulator and no return line. It runs one pressure all the time. Pretty much everyone told me this was destined to fail and that I would need a boost referenced unit. It works great. There were no issues tuning it. I would do it again in a heartbeat.

That can work if the injectors are big enough, but you can run much smaller injectors if the regulator is boost referenced. Most fuel pressure regulators have a vacuum reference that also works as a boost reference.

Braided hoses are fine - although some seem to have long term deterioration issues with fuel. It's not a pressure problem, though.

Depending on the MS version, you may want to use injector resistors.

TheV8Kid wrote: More Questions 1. Where should the pump be located in relation to the fuel tank?

Either in the tank or as close to it as possible and, if possible, below the fuel level.

2. Is this cable adequate for a relay cable? I have read that some of the wires need to be beefier.

A bunch of 28 gauge wires packed in a tight bundle is really only good for signal transmission - it's not a good idea to run any power through it. If you want to save money, skip the relay board; don't try to use a data cable for it.

4. How do you calculate what gallon per minute fuel pump is required for a certain horse power level?

Rule of thumb is around 0.55 lb/hr per hp for a naturally aspirated engine, 0.65 lb/hr per hp for a boosted one. Then multiply by 1.3 to leave a bit of reserve capacity.

A 255 lph Walbro typically works for around 500 hp.

I think you may want to start with your injectors and work your way back. what's the fuel rail setup? many stock fuel pressure regulators are like this:

they have a vacuum reference, a return outlet that gets a hose connection and a port that comes off the fuel rail w/ an o-ring. you might just need to find one that matches the port on the fuel rail, then you can run it as-is, or using a socket in a vise, you can crush it down some to increase the pre-load of the internal spring and raise the base pressure.

if your fuel rail setup does not have a port for an fpr, then you need to find a regulator that has a feed and return with hose connections, or there are options for running with a non-referenced fuel pressure setup. many late model GM LSx stock setups are like this. they use a return-less fuel line setup with the regulator built into the fuel filter. it's a fairly high base pressure, I want to say like 4 bar (~58 psi).

also, happened to come across this when looking to see if there was a stock fuel rail you might be using:

http://m.grassrootsmotorsports.com/forum/grm/turbo-ford-i6s/36236/page1/

Ditchdigger wrote: Most folks say you have to use a manifold referenced regulator but I haven't found this to be the case. For packaging purposes I used a GSXR fuel pump in my fiat with the internal regulator and no return line. It runs one pressure all the time. Pretty much everyone told me this was destined to fail and that I would need a boost referenced unit. It works great. There were no issues tuning it. I would do it again in a heartbeat. You don't get much added fuel with even a 10psi pressure bump. With standalone and fixed fuel pressure the only difference is that some numbers on the map will be higher or lower than if you had referenced. A boost referenced regulator is a good tool for modifying a car with an OEM ECU but with standalone it is just an extra thing to buy.

the reason to go with a boost referenced regulator is that is assures that the fuel pressure at the injector pintle remains consistent through the boost/vacuum range, which makes it much easier to tune as well as give the fuel injector a much wider operating range.

For example, if you run a 45 psi fuel pressure at atmospheric pressure, there is 45 psi pushing fuel out of the injector. If you have the same 45 psi of fuel pressure trying to push fuel out into the manifold runner that already is at a pressure of 15 psi of boost, you actually only have an effective 30 psi of pressure pushing fuel out of the injector, which means you have to add more pulsewidth to the calibration to get adequate fueling. The more boost you add, the more of an effect the lack of boost referenced pressure has. The opposite holds true when in vacuum...you'll have to pull that much more pulsewidth out to make up for lack of boost referenced pressure. You make the injector act like a smaller injector in boost and like a larger injector in vacuum.

OEMs have been moving towards fixed pressure systems for the last decade or so. I think it is just different than what everyone is used to.

My car tuned just great at 21 pounds of boost with a steady 43psi fuel pressure. James (the dyno operator/tuner) didn't notice a difference. I asked him if it caused any problems since everyone told me it would and he simply said no.

I guess I am just saying that if you are starting from scratch creating a fuel system and choosing injectors the correct size that you don't need a fancy high dollar aftermarket fuel pressure regulator. If you have injectors that are too small and need to bump up the pressure than it might behoove you to get larger injectors instead.

Aeromotove -6 regulator

Install it at the end of the fuel rail so it circulated fuel across the rail and also will purge any air bubbles in the rail.

I avoid SS braided hose, anything it rubs on gets eaten up like a hack saw, broken wires leave your hands a bloody mess, offshore MFGRs use crappy rubber, ridiculously expensive. Autoparts stores have standard fuel line that is rated for fuel injection pressures. Push lock hose would be an option but again overkill.