cut-off switch
On our old car when we go to the track,we install a cut-off switch on the alternator,because at hight rpm the alternator rob horsepower.We make the 1/4 on the battery,can we make thet on a ssei 1994???On a old chevy 350 the rpm at idle raise 200 rpm .If we can make it on a ssei 1994,which wire we install the switch??just for the run at the track.
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No, most fuel injected GMs from like '86+ rely highly on the alternator, and the car will most likely stall out or die when you cut the alternator off, as the PCM needs a signal from the alternator.
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the signal is not from the battery?but from alternator??if the alternator fail the car stall immediatly???we can't drive on the battery for few distance??
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Pretty much from experience, when I disconnected the positive cable from the alternator on my '94, the car stalled with a known, good alternator.
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This is why a little battery corrosion on the cables can kill your car.
You don't want to anyway. Your ignition coils need the highest input possible to produce the hottest spark possible. With a battery only, you'll have a weak spark. |
I just ask this because we can make that on our old car ...we installed a 1000 amp bat and we make the run without alternator (I think the car needed a litlle voltage because we don't have pcm) it was just for 1/4 ......sorry for my english
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Amps will get you nowhere for spark. You step up the voltage through a coil (transformer) and the current drops proportionally to the voltage gain.
Voltage is what allows you to jump a spark gap, not current (amps). |
Let's put this another way. Based on a known coil:
The MSD 8224 coil has a turns ratio of 80:1 At 12VDC that equates to a spark voltage of 960 V. At 14VDC (typical alternator output) that voltage is 1,120. 15-20% hotter spark. I'll keep my alternator. |
Let's look at this.
200A * 14v = 2800W = 3.75Hp So even a 200A alternator at full load is pulling less than 4Hp. Even the hottest MSD ignitions are pulling less than 10A at 6000rpm. During a run at the track (lights, AC, stereo all off) the alternator has less than 50A load. 50A * 14v = 700W = 0.94Hp This is less that the run to run variation you will see on a dyno. The extra weight of the bigger battery costs as much as the gain from the alternator shut off. |
The ICM boosts the voltage going to the coils, so spark output is a lot more than 1,000 volts. Somewhere around 30,000 volts IIRC. So at 15% you'd be more like 30,000 vs 34,500 volts.
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I threw that at him as a basic comparison because I couldn't find the ICM ratio spec. ;)
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Race specific batteries are available that offer higher voltage. The ones I have seen are 16 volts though. I don't think that the PCM would like that....
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when my alt seized up... my car made it hmmm MAYBE a quatermile before the battery died.. and it didnt have POOP for power running off just the battery...
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