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  1. #1

    Does CMD remove need for rising rate?

    Just want to validate my thoughts on fuelling with CMD & rising rate RRFPR.

    Assuming that you are tuning against MAP pressures and have created fuel tables against this in CMD, does this completely eliminate the need for using a vacuum reference line on the RRFPR?

    I guess also that once you get the fuelling shape close, you can run Autotune from there (maybe knocked back to maximium change 3%)?

    The rising rate through vacuum reference was an early pressure related fuelling solution that is now too rough and crude to hit tight AFR targets, fair??


  2. #2
    Matatan tocullo's Avatar
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    Correct! No need for raising rate with the CMD.... Static at 58lb should be enough and all you need, CMD will do the rest.

  3. #3
    I just love CMD more and more each day.
    Last edited by tornado34; 06-26-2014 at 04:24 AM.

  4. #4
    boost junkie skidoochris's Avatar
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    rrfpr is a important part to have
    the cmd can only work if you have enough fuel
    injector duty cycles in the 90s are not safe or reliable
    most injectors will not work correctly below 43psi
    so any boost above 15psi your asking for trouble

  5. #5
    imp0ster's Avatar
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    Quote Originally Posted by skidoochris View Post
    rrfpr is a important part to have
    the cmd can only work if you have enough fuel
    injector duty cycles in the 90s are not safe or reliable
    most injectors will not work correctly below 43psi
    so any boost above 15psi your asking for trouble
    1psi boost = -1psi from the injector. a referenced FPR uses that same psi to push back against the boost forces equalizing the pressure.

    Don't listen to any yahoo claiming high boost with FP in the 40s on a static setup.

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  7. #6
    So, correct me if I'm wrong. If you don't reference the FPR and just use monster injectors to allow a good duty cycle, you have to back the fuel pressure right back to stop running too rich in the mid range? Also large injectors screw up the idle and bottom end right?

    So why can't you find a good injector size to give a safe max duty cycle, but not too big to screw the lower band of AFR's. Then let CMD control the fuelling from the MAT? Is this a dream scenario that just isn't possible in the real world?

    Not disagreeing, just trying to fish the bones out of the situation.

  8. #7
    imp0ster's Avatar
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    Absolutely not. Say you push 15psi and start at 58lbs base pressure. At WOT, 15psi, your effective fuel pressure is now 43psi, bordering non atomization. My effective FP at WOT is 46psi since my base pressure is 62psi. ANything more than 15psi and you should really setup for the boost reference line and tune the IFR table for it.

    You typically want your injectors duty cycle below 80% allowing for blips in RPMs and unknowns.

    A good injector will have controlability at lower RPMs, such as Image Dynamics. The injectors on off time plays an important role in lower RPMs. There are tables within the ECU we don't have access to with VTECH

    Before you start messing with your ECU you should learn tuning basics. HP Tuners has a wonderful library of information

  9. #8
    Quote Originally Posted by imp0ster View Post
    Absolutely not. Say you push 15psi and start at 58lbs base pressure. At WOT, 15psi, your effective fuel pressure is now 43psi, bordering non atomization. My effective FP at WOT is 46psi since my base pressure is 62psi. ANything more than 15psi and you should really setup for the boost reference line and tune the IFR table for it.

    You typically want your injectors duty cycle below 80% allowing for blips in RPMs and unknowns.

    A good injector will have controlability at lower RPMs, such as Image Dynamics.

    Before you start messing with your ECU you should learn tuning basics. HP Tuners has a wonderful library of information
    Ok, so it's starting to become clearer. How stable and predictable is the rrfpr off a ref line? Afterall, it's a very simple diaphram. Is it fast to respond? If you set it up perfectly (assuming conditions stay identical) Then you chop around on the rpm, would the pressure be so predictable that the AFR would remain intact? (As much as running static with a properly engineered fuel table?

    Just feels a bit 18th century way of shifting fuel pressure, I kind of want a digital solenoid or something whizzy?? Instead a rubber hose feeding pressure onto a diaphram. Almost as "close" as the oem ballbearing and spring strip??

  10. #9
    imp0ster's Avatar
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    get yourself an aeromotive compact EFI regulator. There's a reason drag cars use them. There's a reason a lot of us sue them. I used one on my 30psi grand prix. Don't cheap out here

  11. #10
    Quote Originally Posted by imp0ster View Post
    get yourself an aeromotive compact EFI regulator. There's a reason drag cars use them. There's a reason a lot of us sue them. I used one on my 30psi grand prix. Don't cheap out here
    Will look into that, sounds more like it.

    So cutting to the chase, I'm gonna put in the 137+4 which says "13-13.5 psi of boost @ 8100 rpm and 15 psi + @ 8500rpm", so assuming that I don't pass the 15psi mark, would me OEM 48# max out under a static 58psi fp?

    Is there a better injector that will be ok bottom & mid range as WOT is so little of my ride time?

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