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Current and voltages during start on a 72 383 small block with MSD ignition

bikeron

Veteran Member
Senior Member
Fuse box voltage is the green trace (4) at 2V/div, Battery voltage is magenta trace (same reference point as (4) at 2V/div), Battery current is the yellow trace (1) at 20 amps/div (not including the current from the battery to the starter; that is shown in the blue trace (2) at 500A/div) with zero current reference at center line (current from battery is above the center line while current into the battery from the alternator is below the center line). Note the MSD box noise; not good for radio/stereo. Solenoid takes about 38A peak current to engage the starter for 20 milliseconds then drops to something less than 18 amps, perhaps 16A, while the starter is active.
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Back in 2019 I switched out my MSD 6AL out to the 7AL2 I got form my good friend (now passed on) and the difference was very impressive. The car idled 600rpm higher with the 7AL2 over the smaller box and every engine in the car does not miss a beat. This box sure does shoot a good spark also.
 
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