Unloading alternator for several free HP

Discussion in 'High Performance Modifications' started by CanadaGreg, Feb 20, 2005.

  1. CanadaGreg

    CanadaGreg Veteran Member

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    "There are several ways of making free horsepower on most older cars. When an alternator "energizes", and loads down, it can suck up about 8 to 12 horsepower. Don't believe me? Fine. Just listen to your engine lug down 50 to 100 RPM when you hook-up some jumper cables to jump start a friend with a dead battery. That my friend's is the alternator lugging the engine down under a load. If you are racing at night with your headlights on or your battery is a little low... then your engine is being put through the same "load" as you're racing down the track. You can gain this HP back by simply installing a switch in the "field" wire to shut it off. The field supplies the alternator with electricity which energizes it, or basically, turns it on. Alternators need electricity to work, unlike old generators. If you don't allow this field wire to energize the alternator, you have gained a few more ponies. You MUST turn the engine off first and make sure the key is off as well when the switch is turned off, or the alternator will NOT "de-energize". So remember... you must turn the switch off before you start your engine. Once the engine's running and you want to re-energize the alternator, simply flip the switch while you're driving and it instantly turns-on."


    I grabbed this off of http://badasscars.com/techtips.html#free and I was wondering if someoney had any experience with doing something like this before. I would love to get a few extra hp with a fairly stright forward electrical mod.

    Thoughts? What about the good an alternator does in maintaining voltage? I'll be adding an electric fuel pump to my car when I go EFI and I'm thinking the reduction in voltage to the pump would be a concern (for example). Impact on ignition?
     
  2. Mwilson

    Mwilson Veteran Member

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    I just went outside and wired a toggle switch to my alternator!
     
  3. HEAVYchev

    HEAVYchev Veteran Member

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  4. 1978LT

    1978LT Veteran Member

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    Darn, and I was thinking of upgrading to a 100 amp unit [​IMG] I figured unhooking the alternator would be worth 4 hp max.
     
  5. Bondo79

    Bondo79 Veteran Member

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    it is unless there is some load placed on it.
     
  6. milbroman

    milbroman New Member

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    I'S NO SECRET BEEN TOGGLING THE ALT ON THE RACE CAR FOR EVER ITS THE DIFERENCE WHEN ALL YOU NEED IS ONE CAR LENGTH
     
  7. CanadaGreg

    CanadaGreg Veteran Member

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    Hmmm. I'd say this is worth more investigation. I don't have any type of engine dyno or anything. But I have a megasquirt and i should be able to tell something by the datalogging. I'll run the car through the gears with and without the alternator and compare which is going through the RPMs faster (no speed sensor on anything but engine).

    This is of course when I get the car on the road (hopefully this summer). Darn being in college!!

    Thanks guys
     
  8. Joekool

    Joekool Veteran Member

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    You might free up 12 hp if you have an 80 amp load on your charging system, but if you just have a 20 or so amp load your not going to gain that much hp. In the old days you could turn off everything (head lights, radio, heater etc) and drive for 2 or 3 hours with no problem, with a new car your lucky if you get an hour of reserve out of the battery, EFI, DIS, ABS and all the other electronics draw current, even with the car off most new cars draw upto 200 milli amps, thats a constant load at all times on your bat.

    If your hardcore go for it, me I like my stereo, heater and other electric stuff to work right so Ill just sacrafice that 4 hp.
     
  9. onovakind67

    onovakind67 Veteran Member

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    The average alternator is about 50% efficient. One horsepower equals 746 watts, or 51.5 amps produced at 14.5 volts. Turning off an alternator that is producing 51 amps will save you about 2 horsepower at the crank. In order to save 12 horsepower, you would have to be dissipating about 7500 watts in the alternator, and that sucker would be red hot.
     
  10. Mathes79Z

    Mathes79Z Veteran Member

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    Cut off the alternator and gain what, 4hp max..
    that cuts your ignition from 14.7 volts to 8 loaded volts, loss of roughly 8-20hp from ineffecient fire.
    fuel pump speed drops which drops pressure and ability to keep up with high rpms, now you cant rev to 6000rpms because of ignition and fuel.
    oh yea, now your cars a real badass.
    if nothing else, at least underdrive your alternator.
     

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