Brooklyn Beer Posted April 28, 2020 Share Posted April 28, 2020 I have a 1939 Chrysler Royal on it's way and after doing a web search I see choosing a spark plug is a very personal choice. But one thing I see is as many people choosing a resistor plug over a non resistor plug. So I was hoping someone with a greater set of electrical skills can tell me what really is the difference of running either in a stock 1939 motor ? And what plug would you run? Link to comment Share on other sites More sharing options...
Pete O Posted April 28, 2020 Share Posted April 28, 2020 Since resistor plugs weren't developed until the '60s, a non-resistor plug would be standard for a '39. And as the last paragraph below mentions, a resistor plug delivers a lower energy spark. All the more reason not to use a resistor plug in a car that was not designed to require one. Link to comment Share on other sites More sharing options...
Rusty_OToole Posted April 28, 2020 Share Posted April 28, 2020 I would use a non resistor plug of the same make and type as recommended by the manufacturer of the car. Didn't Chrysler use Autolite as standard equipment? I would use solid core spark plug wires same as original equipment and if I wanted it to start and run in all weather I would buy the Everdry spark plug boots from Bernbaum. BUT I would use a resistance wire for the coil wire in the interest of radio suppression. 2 Link to comment Share on other sites More sharing options...
Bloo Posted April 28, 2020 Share Posted April 28, 2020 (edited) I doubt a resistor plug delivers a lower energy spark. Maybe a little lower. The resistor would raise the firing voltage by a little but probably not a lot. The old standard advice was to never use both resistor plugs and resistor wires on the same car if it had a points ignition. Once resistor wires became available, anything that had a radio probably had them for interference suppression. That meant non-resistor plugs always for old cars. Looking back with more understanding of how ignition systems work, I think that might be an old wives tale. From a practical standpoint, in 2020, almost all non resistor plugs have been discontinued, and some heat ranges discontinued altogether, even in resistor plugs. What plugs are they offering to fit a 39 Chrysler? I too would run non-resistor plugs if I could get them. My Pontiac has lawnmower plugs in it. Where theres a will theres a way..... Edited April 28, 2020 by Bloo (see edit history) 1 Link to comment Share on other sites More sharing options...
Brooklyn Beer Posted April 28, 2020 Author Share Posted April 28, 2020 I tend to ask questions and then look to see what other are running and make comparison. I find Rock Auto a good source because of the spec's they give. MOTORCRAFT SP473A {#SP473} Info w/ Aluminum Head; .025"/0.6mm, OE Style; Non-Resistor Plug; Copper $0.71 Add to Cart AUTOLITE 295 {#295DP} Non-Resistor Info .025 Gap; Non-Resistor Plug; OE Style; with Cast Iron Cylinder Head $1.01 AUTOLITE 306 Resistor Info .025 Gap; Resistor Plug; with Cast Iron Cylinder Head $1.19 Add to Cart AUTOLITE 216 {#216DP} Non-Resistor Info .025 Gap; Non-Resistor Plug; OE Style; with Aluminum Head $1.22 Add to Cart ACDELCO R45 {#19307612, 19354428} Professional; Conventional (Rebate/Promotion Available!) Info Gap .025; With cast iron heads $1.42 Add to Cart MOTORCRAFT SP480 {#A7C} Copper; Non-Resistor Info OE Style; with Cast Iron Cylinder Head; .025"/0.6mm; Non-Resistor Plug; Copper $1.42 Add to Cart CHAMPION 511 {#J11C} Copper Plus Info with Stock Cast Iron Heads, Non-Resistor Type; Gap .025" $1.52 Add to Cart ACDELCO C45L {#01559452, 19310645, 19422133} Professional; Conventional Info Gap .025; With aluminum heads $1.53 Add to Cart CHAMPION 592 {#RJ12C} Copper Plus Info with Stock Cast Iron Heads, Resistor Type; Gap .025" $1.75 Add to Cart CHAMPION 854 {#RH10C} Copper Plus Info Aluminum Heads; Gap .025" $1.93 Add to Cart Platinum (lasts up to 2x longer than copper) ACDELCO 7 {#19238458, 19360569, 25171346} Professional; Rapidfire (Rebate/Promotion Available!) Info with Stock Cast Iron Heads; Gap .025" $2.92 Add to Cart Double Platinum (lasts up to 3x longer than copper) ACDELCO 41833 {Click Info Button for Alternate/OEM Part Numbers} Professional; Double Platinum (Rebate/Promotion Available!) Info with Stock Cast Iron Heads; Gap .025" Link to comment Share on other sites More sharing options...
Pete O Posted April 29, 2020 Share Posted April 29, 2020 I have an old Chilton's manual that goes back to 1940, and that shows the oem sparkplug for Chrysler was an Autolite A7. I imagine 1939 was similar. You can still buy these: https://donsautoparts.com/spark-plugs/catref/spark-plugs/ref/bo185/older-copper-core-spark-plug-autolite-a7 Link to comment Share on other sites More sharing options...
FLYER15015 Posted April 29, 2020 Share Posted April 29, 2020 I run a set of A.C. Delco C-49's in my '31 Imperial 8, and my '40 Buick 8. They are a commercial, copper cored plug, with a little bit "hotter" spec than the 45's or '46's. Still made in quantity today they are spec'd for a lot of stationary generators. Both cars have 'unmolested" (never torn down) engines, and we don't do a lot of high speed cruz'in . Mostly under 55 on state highways and around town, so we don't get a chance to "blow them out". Mike in Colorado 1 Link to comment Share on other sites More sharing options...
The 55er Posted April 29, 2020 Share Posted April 29, 2020 (edited) Maybe this will help. Edited April 29, 2020 by The 55er added pics (see edit history) 1 Link to comment Share on other sites More sharing options...
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