Why do you guys use 2 FPU to adjust fuel?

[GreenHornet]

I know this might be a stupid question but. I don't know how this might be working using 2 fuel pressure units. Wouldn't the Cartech be enough to control the fuel? Why do you guys have to replace the stock one on the rail for a AEM adjustable one? The Cartech does the same thing the Aem does, why need two?

[G3-TEG]

I think you are getting confused in how each of the two unit function and what their duties are.

The Cartech unit and not an FPR (Fuel pressure regulator). The Cartech unit is what is called an FMU (Fuel management unit).

It does absolutely NOTHING until it sees boost and then it will raise fuel pressure at a fixed ratio. In the case of the Cartech, this ratio is adjustable by the user. By using a device such as an FMU, one can increase fuel pressure by the correct amount under boost, but retain stock pressure when not under boost.

The AEM/B&M/Vortech FPR that you are refering to is NOT an FMU device. Meaning it doesn't NOT react to boost conditions. All it will do is allow the user to set the base fuel fuel pressure (ie. at idle). This mean that the user can set the base idle to say 40psi. Then when the car reaches boosted conditions, the Cartech or other similar FMU will raise the fuel pressure according to its rising rate ratio and calculate that new fuel pressure based on the original base pressure that the user had set with the AEM FPR.

Basically, if you set the idle pressure higher, then the end result under boost will be a higher fuel pressure and vice versa. The ratio of the FMU would not change if you changed the idle fuel pressure with the FPR.

Cool?

[GreenHornet]

The cartech can adjust Idle pressure too. Does the pressure regulator adjust the fuel idle even more or what? I know the cartech can adjust the boost to raise the fuel but it can also adjust he idle pressure. So is there still a need for the Aem/b&M regulator?

[zip]

Yes, you still need some sort of fpr that raises fp's from idle vac to atmosphere. Holden just found out that the AF mixture leans out for a brief moment until the FMU starts to increase fp. Most of our driving involves in the vac area, where the FMU has a difficult time maintaining decent fp's. Most, if not all, FMU's were made to be inline w/ a fpr. You can also think of the fpr as insurance just in case the FMU craps out one day.

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Mods

[Holden]

If you're running 8psi or less, you may be able to use just a cartech. Without the restrictor in its' vacuum line, it does an OK job taking care of FP from idle to 0"vac.

Apparently at 8psi or less, the bleeder valve can still bleed off enough air (boost) to control the rise rate. I'm at 10psi, and even though I now have no restrictor and the bleeder wide open, FP is still rising at about a 5:1 ratio which is way too much for 320cc injectors.

Once the restrictor is in the line, max FP is controlable again, but the cartech does not react quick enough to handle sudden throttle openings, and you'll go lean and perhaps detonate, or in my case, go so lean my mix became uncombustable and it was like the engine turned off for a second until the cartech caught up.

Check out my topics on bogging.

Greg

[gsrev]

I donno about all that... I have a cartec and I have completely eliminated my fuel pressure regulator on the rail. I don't have a bog at all and my idle pressures are at 28psi w/ 320cc injectors. I just jb welded a fuel nipple in its place

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1992 Red Honda Civic CX Hatch Back
B18C1 hybrid
JRSC 12 psi and bunches of goodies to go along
ET drags 22x8x15 for the strip and 205/45/15 nitto 555r for the street

1998 Super Sonic Blue Integra GS-R (completely stock now)
With jrsc at 6psi best 1320: 13.783 @101.43 on drag radials

[Holden]

gsrev: What is your max FP at 12psi boost?

Are you using the restrictor?

Mine is flying up into the 90's at full boost now (no restrictor, no bog) and I know that I've done detonation-free 1/4 runs with a max FP of 67.

Greg

[nexusone]

If the AEM and Vortech and such are NOT reactive to boost pressure then why do so many people use them for FI applications? According to the literature available they are reactive just like the Cartech. Are you sure about this?

[texasteg]

I think you may be confused. Vortech makes a FMU similar to the one made by CARTECH. AEM, on the other hand, makes a FPR that is not controlled by boost.