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GM LS3 crank wheel gap/TDC relationship 
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TO92 - Vaguely active

Joined: Tue Dec 09, 2014 7:50 pm
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I am working on an ignition design for a carbureted LS3, and I'm trying to find the timing relationship between the gap in the crank sensor wheel (the 58x wheel) and the crank position. I saw in a couple of places the statement that the GM 58x gap "starts at 30 deg ATDC of cyl 1", but in looking at the LS3 I have on the stand, that does not seem to be correct. If I turn the crank by hand, the leading edge of the gap (i.e. where the last tooth trailing edge starts) is about 5 BTDC for cyl 3 (the last cylinder in the sequence), or 95 deg BTDC of #1. The gap ends at 80 deg BTDC #1, so it is about 15 deg wide. I can't seem to reconcile this discrepancy. Does anyone know what the gap AT THE SENSOR relationship to TDC #1 is?
Dave T.

Tue Dec 09, 2014 11:50 pm
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TDC #1 is what you want, but you need to think in terms of sensor position, and what type of sensor you're using. IE, VR means middle of tooth, likely one on one side of the gap. Hall, on the other hand, means one edge of one of the same teeth, depending upon how it's setup. Measure this yourself, the internet is full of bullshit :-)

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