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  • OBX 12.1 fuel pressure regulaor

    Long story short, i need a fuel upgrade, I hava a t3-4 turbo, big exhust, cams, Z32 fuel pump, stock injectors and ECU. Will a OBX 12.1 fuel pressure regulator hold me over untill I install 370 injectors, z32 MAS, and a romulator. Or should I just install a fuel pressure gauge and crush my stock fuel regulator.

  • #2
    keeping the boost at a level that your stock fuel system can handle will hold you over until you upgrade the fuel system properly. my opinion, do it right or dont bother.

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    • #3
      How much boost are you running now?
      imagination is a virtue

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      • #4
        OBX 12.1 fuel pressure regulaor

        about 6-7 lbs I have a apex adjustable boost guage

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        • #5
          edsz31 wrote: about 6-7 lbs I have a apex adjustable boost guage
          Good, leave it there for now.
          You could crush the regulator for up to ~50psi base pressure with the risk
          of destroying it in the process. Then bump the boost to ~9-10psi.
          And back out the timing a couple degrees for safety.
          It will have bad mpg and a possible crappy idle.
          Of course this is far from ideal and mearly a bandaid solution,
          but ultimately it is your decision and your own risk.
          If you do this it is highly advisable to get on a dyno or anything with a wideband afr meter to make sure you arent going lean.
          imagination is a virtue

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          • #6
            Here is the VERY poor mans way to do fuel upgrades but it is not adviseable. But I will tell you anyways cause its not my car and I dont care

            Get an adjustable FPR then install those 420cc injectors that everyone seems to love and turn your base fuel pressure WAY down, the car will barley idle but at wide open throttle and around redline your car will have an OK afr and make more power as well. I had a buddy run low 12's/ high 11's with his fuel system that way. He also had a high pressure fuel pump too. good luck and yes, it really works! :shock:
            "Simplify and add lightness."
            "Adding power makes you faster in a straight. Losing weight makes you faster everywhere."

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            • #7
              Merovingian wrote: Here is the VERY poor mans way to do fuel upgrades but it is not adviseable. But I will tell you anyways cause its not my car and I dont care

              Get an adjustable FPR then install those 420cc injectors that everyone seems to love and turn your base fuel pressure WAY down, the car will barley idle but at wide open throttle and around redline your car will have an OK afr and make more power as well. I had a buddy run low 12's/ high 11's with his fuel system that way. He also had a high pressure fuel pump too. good luck and yes, it really works! :shock:
              Exactly. Engines don't care how they get it, as long as they have the fuel and timing requirements met for how they are run.

              You can go either way by upping pressure or using higher flow rate injectors and lowering the pressure. Keep in mind fuel atomizes better with higher pressure, but pump flow falls off. With a walbro, I would say cranking the pressure is a more economical bandaid.

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              • #8
                What about putting those 370cc injectors in, and wiring a pot into your AFM signal wire to adjust the mixture by fooling the computer?

                You basically get 2 10K pots, the first pot has +5V (or +7, whatever the z31 maf runs off) on one end, earth on the other and the centre terminal connects to one of the outside terminals of pot 2. Then you connect the AFMs signal wire to the other side of pot 2 and the centre terminal to the ecu. Set them both to centre position, start the car with the O2 sensor unplugged and use pot 1 as the coarse adjusment and pot 2 as the fine adjustment. Apparently it works, but i havnt tried it. Its basically like an S-AFC so 370cc injectors will be ok, just dont over do it with boost cause your timing will be advanced cause the ecu has been tricked.

                That mod will cost you a couple of bucks from your local electronics shop.

                Try at your own risk

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                • #9
                  FMU

                  Will a Fuel Managment Unit, like 12.1 work as well as a AFR (adjustable fuel regulator if I want run my stock injectors?

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                  • #10
                    you cant use a 12:1 ratio unless you have some sort of bleed valve on the vacuum line (MBC). You will be locking your injectors from too much pressure. Have a read of Jasons write up on FMUs on his site.

                    You need to read about the effects of fuel pressure on the injectors. Then you will be able to work out what ratio is appropriate. With any of those FMUs you will be running too rich during the levels of boost you most use, just to run a couple of PSI more.
                    The FMU Jason had (i think it was cartech) had an adjustable threshold. You only want to boost the fuel where it is needed, up to 8-9PSI, the computer can supply the correct ratio, making it richer will kill economy and reduce power. Is it worth it when your planning on upgrading later?

                    Only a year or so ago, FMU's were a possible solution for the Z31 due to JWT's high prices and lack of people like Jasons research and experimentation. Now you can buy a Romulator for not much more than an ebay FMU vortech, Blox etc.

                    If i were you and really planning on getting the Romulator, z32 MAF and injectors, i would buy the romulator now instead of the FMU, get a cheap adjustable fuel reg off ebay, raise the base fuel pressure and adjust the K value accordingly. At least then you are not wasting money on something that you will be getting rid of.

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                    • #11
                      Liam86t wrote: What about putting those 370cc injectors in, and wiring a pot into your AFM signal wire to adjust the mixture by fooling the computer?

                      You basically get 2 10K pots, the first pot has +5V (or +7, whatever the z31 maf runs off) on one end, earth on the other and the centre terminal connects to one of the outside terminals of pot 2. Then you connect the AFMs signal wire to the other side of pot 2 and the centre terminal to the ecu. Set them both to centre position, start the car with the O2 sensor unplugged and use pot 1 as the coarse adjusment and pot 2 as the fine adjustment. Apparently it works, but i havnt tried it. Its basically like an S-AFC so 370cc injectors will be ok, just dont over do it with boost cause your timing will be advanced cause the ecu has been tricked.

                      That mod will cost you a couple of bucks from your local electronics shop.

                      Try at your own risk
                      I actually tried something very similar to that. It's a maf voltage drop from the POT, but the problem is that the voltage curve from a maf is not linear. If you shift the cirve one way or the other, it may run right under boost but not under light loads or vise versa. At least that's what I discovered... you would need to somewhat extensively modify the afm's VQmap or the primary fuel map to get a voltage dropped car to run correctly in all conditions, and if you have that ability then the only reason you would be dropping the voltage would be to extend metering ability.

                      The secondary problem is not being able to tune for injector void time, which if you think about it may even further aggravate the first situation.

                      I know guys on hybridZ.org use 370cc injectors and put the maf in a larger housing (3.5" I believe) then trimming using fuel pressure and the POT on some factory MAF's. This is the same basic thing, except dropping the signal voltage mechanically (the voltage put out by the maf) instead of electrically (modification of the signal after the maf). If you think about how a maf transfer function (called a VQmap for our ECCS) is shaped and the resolution on either end, you will see why using a larger housing or building an air bypass should be technically better than adjusting the voltage drop using a POT.

                      At least that's from my experience... tell me if this made any sense.

                      And yes, I dealt with that same RRFPR question when Kevin (88hybrid) could not figure out why he screwed up his car and ended up blaming the equipment instead of himself, as most people do. That's why I put it on there.

                      Comment


                      • #12
                        [quote]Jason84NA2T wrote:
                        Originally posted by Liam86t
                        What about putting those 370cc injectors in, and wiring a pot into your AFM signal wire to adjust the mixture by fooling the computer?

                        You basically get 2 10K pots, the first pot has +5V (or +7, whatever the z31 maf runs off) on one end, earth on the other and the centre terminal connects to one of the outside terminals of pot 2. Then you connect the AFMs signal wire to the other side of pot 2 and the centre terminal to the ecu. Set them both to centre position, start the car with the O2 sensor unplugged and use pot 1 as the coarse adjusment and pot 2 as the fine adjustment. Apparently it works, but i havnt tried it. Its basically like an S-AFC so 370cc injectors will be ok, just dont over do it with boost cause your timing will be advanced cause the ecu has been tricked.

                        That mod will cost you a couple of bucks from your local electronics shop.

                        Try at your own risk
                        I actually tried something very similar to that. It's a maf voltage drop from the POT, but the problem is that the voltage curve from a maf is not linear. If you shift the cirve one way or the other, it may run right under boost but not under light loads or vise versa. At least that's what I discovered... you would need to somewhat extensively modify the afm's VQmap or the primary fuel map to get a voltage dropped car to run correctly in all conditions, and if you have that ability then the only reason you would be dropping the voltage would be to extend metering ability.

                        The secondary problem is not being able to tune for injector void time, which if you think about it may even further aggravate the first situation.

                        I know guys on hybridZ.org use 370cc injectors and put the maf in a larger housing (3.5" I believe) then trimming using fuel pressure and the POT on some factory MAF's. This is the same basic thing, except dropping the signal voltage mechanically (the voltage put out by the maf) instead of electrically (modification of the signal after the maf). If you think about how a maf transfer function (called a VQmap for our ECCS) is shaped and the resolution on either end, you will see why using a larger housing or building an air bypass should be technically better than adjusting the voltage drop using a POT.

                        At least that's from my experience... tell me if this made any sense.

                        And yes, I dealt with that same RRFPR question when Kevin (88hybrid) could not figure out why he screwed up his car and ended up blaming the equipment instead of himself, as most people do. That's why I put it on there.
                        Yes that makes sence, I would much rather run a mechanical solution to drop the voltage rather than jacking with the actual voltage out put on the maf its self. That and if you do it correctly you can make your MAF bypass adjustable to whatever you need(within reason) just by opening up or closing down a large version of say a mechanical boost controller(not a bleed style).
                        85 Z31 6.0 LSX turbo 766whp/792wtq
                        04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.

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                        • #13
                          Yeah like i said, i havnt done it, only read about it. I was unaware that the AFM signal wasnt linear, but that shouldnt matter should it? If its using the reference from the maf signal then it should shift the whole map forward or back should it not? I havnt bothered trying it because even if you get it to work, the timing will be all wrong anyway. Obviously what you were doing with it is totally different cause you had controll over the ecu.

                          As for needing to upgrade the MAF, thats another reason i want to use Megasquirt. Dont think il be getting to 21PSI in a hurry and even if i do another map sensor is half the price of a maf.

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