Woodie Posted October 31, 2023 Report Share Posted October 31, 2023 I came across some NOS Auto-lite A-5 spark plugs (factory recommended originally for my 48 Chrysler). Although both old and new have A5 on them there is a plug height difference. - would the shorter height one run hotter since the spark path is shorter? The shorter one has a military spec number on the Auto-Lite box. comments? Quote Link to comment Share on other sites More sharing options...
Sniper Posted October 31, 2023 Report Share Posted October 31, 2023 What makes a plug hot or cold is the path from the center electrode to the metal shell, that is inside the plug. Eternal lengths are not really part of it. Quote Link to comment Share on other sites More sharing options...
Woodie Posted November 1, 2023 Author Report Share Posted November 1, 2023 Thanks Sniper - another thought was that these shorter plugs were for heads that were flatter from the top head surface to the well the spark plug fits in - as new design heads came out with deeper spark plug wells they raised the height so plug wires wouldn’t short out and jump to the head. The packaging of the shorter plugs look like they were for maybe 30’s Mopars. Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted November 1, 2023 Report Share Posted November 1, 2023 I looked in my Autolite sparkplug literature that covers from 1930-1939. The only reference for the A5 was for the Hudson. Refer to the attachment below. for High speed driving C. I Hd from 1936-1939. The A 5 is a colder plug according to their chart. Rich Hartung Desoto1939@aol.com 1 Quote Link to comment Share on other sites More sharing options...
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