MarcDeSoto Posted July 27, 2022 Report Share Posted July 27, 2022 I have an old box of NOS Autolite spark plugs AR 10. Should I use these in my rebuilt 1948 DeSoto engine, or buy new ones? When I open each box, the spark plug is wrapped up in a paper coupon that can be turned in for prizes. The coupon says it expires on December 31, 1945! I guess I'm a bit late for the prizes. 1 Quote Link to comment Share on other sites More sharing options...
SteveR Posted July 27, 2022 Report Share Posted July 27, 2022 They look a bit rusty so I would clean them up so you have a good ground. There isn't anything perishable inside so they should be good to go. Nice touch for a concourse event. Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted July 27, 2022 Report Share Posted July 27, 2022 what gap are you planning to use. Might have to be set at 35 for the resister plug versus regular at 25. Rich Hartung Quote Link to comment Share on other sites More sharing options...
Conn47D24 Posted July 27, 2022 Report Share Posted July 27, 2022 I use A-5 NOS in my D24 Quote Link to comment Share on other sites More sharing options...
MarcDeSoto Posted July 28, 2022 Author Report Share Posted July 28, 2022 19 hours ago, MarcDeSoto said: I found out that most of the NOS plugs are A7 plugs, so not resistor. I guess you should use resistor if you plan to play the radio? I still have an A-5 plug from the 80s. Do they still sell them? Should I use a normal plug or the hotter plug on a rebuilt engine? Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted July 28, 2022 Report Share Posted July 28, 2022 A7 was the standard Autolite plug for our cars. The A9 is a hotter plug both of these are non resister plugs. My friend that has a 39 Desoto is running the Autolite 297 plug and you can get them at Walmart they are a small engine plug and cross over and cost around $2.90 a plug. Rich Hartung Quote Link to comment Share on other sites More sharing options...
MarcDeSoto Posted July 28, 2022 Author Report Share Posted July 28, 2022 Should I buy resistor plugs if I am going to play the radio? Quote Link to comment Share on other sites More sharing options...
SteveR Posted July 28, 2022 Report Share Posted July 28, 2022 7 hours ago, MarcDeSoto said: Should I buy resistor plugs if I am going to play the radio? Resistor plugs help suppress spark plug noise, a valuable trait under certain circumstances. However I had a 1965 Plymouth Barracuda with a 225 slant 6. I did not use resister plugs and my AM radio worked fine with no interference from the plugs. I had problems with the FM band and resister plugs were needed. Quote Link to comment Share on other sites More sharing options...
desoto1939 Posted July 28, 2022 Report Share Posted July 28, 2022 They make a radio condensor that goe on the generator that is used to supress the static from the plugs. That is what came with my 39 desoto since the original owner had the factory radio installed and it does work and then you can use regular plugs instead of the resiter plugs. Rich Hartung Quote Link to comment Share on other sites More sharing options...
Sniper Posted July 28, 2022 Report Share Posted July 28, 2022 There are several sources of potential interference. Ignition noises, sounds like crackling/popping. Resistor plugs and wires for that and a cap on the coil supply side terminal if it's bad enough. Wires and plugs can act as antenna radiating the noise as RF and the radio picks it up with it's antenna, the resistance takes care of that. Noise can also feed back in the electrical system, the cap takes care of that. The alternator/generator, sounds like a whine that varies with RPM. It can be a back diode, if it's an alternator, otherwise a cap on the output for that. Pick your poison https://www.summitracing.com/search/part-type/noise-filter-capacitors Quote Link to comment Share on other sites More sharing options...
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