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Thread: +12V while cranking?

  1. #1

    Default +12V while cranking?

    Just curious if the system HAS TO have 12V under cranking? The best I can get out of my system is 10.2V under cranking, and then 12.8 at key-on.

  2. #2
    Join Date
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    No, it won't have 12 volts while cranking anyway.
    https://forums.holley.com/showthread...9369#post79369 (Additional Information)
    Also, ensure the Sniper switched +12V pink wire is powered in the "Run" and "Crank" key positions.
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

  3. #3

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    OK, so then it should fire the computer? Awesome!

  4. #4

    Default

    What is meant by the term "12V when cranking" refers to certain circuits (varies with years & make) in which the ignition switch kills power to some circuits when cranking. Mopars are a particular example. So you have to make sure you do have good power to the EFI during the crank position.

    ANY battery (fully charged 12.6V) will drag down when cranking. "Minimum" voltage claimed varies with what book you read, I personally look for "at least" 10V. More is better. "Back in the day" when all starters were wound field (not permanent magnet, mini starters) and before EFI, you could find cars with a low battery might start clear down to 8V or so "cranking." "Back in" the breaker points days.
    Last edited by 440roadrunner; 05-02-2017 at 03:24 PM.

  5. #5
    Join Date
    Nov 2013
    Location
    Chicago IL
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    1,958

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    Quote Originally Posted by zeppelin264 View Post
    Just curious if the system HAS TO have 12V under cranking? The best I can get out of my system is 10.2V under cranking, and then 12.8 at key-on.
    It doesn't have to have 12V, but it's not gonna fire off at 10.2. The Holley doesn't like the voltage to dip that low.
    Add better Grounds and better Main Power Wires. Get the voltage to only sag to 11.0 ish and you will have no issues.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

  6. #6

    Default

    I'm going to try it at the 10.2V. If it does not work, then I'll add a fused relay off the battery for all my switched accessories.
    I talked with a Holley Tech on the phone, and he said 10.8V is minimum for fire. And a lot of people with older cars just do a relay to supply switched battery power.

    Your right, I need less draw on the system, but the old Mopars have one wire that can be used under the hood for switched power (which goes through the bulk head connector, which I'm sure is where the voltage drop is occurring). Battery in the trunk, so it's a pain to wire anything directly to the battery.

  7. #7
    Join Date
    Nov 2013
    Location
    Chicago IL
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    It's not "Less draw in the system" that you need.
    It's less Voltage Drop because of the existing wires in your car.
    They need to be upgraded to a larger wire diameter (smaller number/AWG).
    A big voltage drop is a sign of wires that are not large enough to supply enough amperage for the device it is attached to (this being your starter).
    A run from a battery in the back of the car to the front should be at least 2 AWG, preferably 0 AWG, or 2/0.
    -Scott
    Don't forget to check out progress on my Race Car:
    Project Blasphemy - 8.07 @ 171
    Low 8 Second Street Car

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