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Thread: HEI VS. MSD 7AL-3

  1. #1
    Senior Member SENIOR BUILDER
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    Apr 2006
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    HEI VS. MSD 7AL-3

    has anyone ran a 9 second car with a HEI then switched to a MSD7AL-3 my question did you pick up et with the MSD?, does the MSD use a lot of power? i have a friend that uses a HEI and does not have to charge between rounds, my msd is a older model and i run a electric fan, procomp electric water pump, mallory fuel pump, alternator & optima red top battery, i have to charge after every run i just bought a Sears charger (charges at 40 amps) seems to take a long time to get 100% charge. thanks for the help Doug

  2. #2
    Senior Member DYNO OPERATOR
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    Jan 2004
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    central Illinois
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    HEI

    For either ignition -- 100 amp alternator and 2 batteries = no charging at track.

    Trickle charge during the week.

    Assuming you have room for all that.

  3. #3
    Senior Member SENIOR BUILDER
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    Apr 2006
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    charging

    Mark i do have 2 batterys but 1 is a red top and the other is a yellow top (deep cycle) and i do have a 100 amp alternator, i pulled the other day because it gets real hot, and it shows on the volt gauge that it is charging, will have it checked out tomorrow, both batteries will charge to 100% if i leave it on long enough. also a friend had me hook up the batterys to a ford type solinoid he said this way the battery with the most power will be used ? thanks for your input Doug

  4. #4
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Doug,
    My two cents on this question. The 7AL-3 uses 1amp per 1000rpm. If you weren't burning all the fuel with the HEI then there would be a power increase with the better ignition. Most HEI units don't like rpm above 6500 or so. I believe it has to do with the coil rise time so and the MSD should be putting out more energy overall. You should be able to burn the mixture better if the HEI is not getting it done.

    Looking at what you are running I would guess total amp draw for the three items you listed somewhere around 37-39 amps. The fuel pump depending on which one it is will probably be around 6-9amps, fan around 14-15amps or so, and the only procomp water pump I have checked pulled 17amps. I have a true RMS clamp on meter that will read DC amp draw that I use when someone wants to know total power used.

    Now I have a some questions. If you are running an alternator why run two batteries? Do you have starting problems if you don't charge between rounds? Have you ever checked total amp draw with the car running, or do you have an amp meter in the car? I see you are checking the alternator.

    Not sure about the solenoid deal??

    By the way I run one of the super mini 50amp alternators and one Sears Platinum 1000amp battery and I never have to charge my car. I do however use one of the Battery Tender brand trickle charger / maintainers whenever the car is just sitting.

    Curtis

  5. #5
    Senior Member SENIOR BUILDER
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    charging

    Curtis i do run a msd distributor, thought a hei might not draw as much as my 7al-3, i added the second battery for better weight (now 53% on rear), i'am dropping off my alternator today it gets so hot you can't touch it even thou it still shows that it is charging, last weekend we got 6 time runs on sat. and would not get fully charged and a couple of times wasn't sure it would start (full charge no problem), i do use the fan and water pump to cool down after a run and it takes some time to get full charge, i will take the car to my alternator shop to check out the draw in 2 weeks (i bowl in a tournement this weekend then have company next week and race woodburn 8/13-14) no time to check it out till later. thanks Doug

  6. #6
    Senior Member RACING JUNKIE curtisreed's Avatar
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    Sounds like you have a plan. No problem with using the extra battery as ballast and gaining a larger reserve of power. Good luck on the lanes. I'm right there with you on the time thing. I am wanting to add some sensors to my data recorder and do some basic maintenance on mine but we bought a new house and we're moving out as we move my son and his fiance' into our old house. :shock: :shock: I'm to old for all this moving crap.

    Curtis


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