Richard Cranium Posted June 17, 2019 Report Share Posted June 17, 2019 So Wags and I are getting set to convert the dragster to fuel injection. The instructions call for resistor spark plugs and I've been running non resistor Autolite Racing AR51 plugs in the car and I'm happy with them. As best I can tell there is no resistor version of the AR51. Does anyone have any good resources to sort out an equivalent resistor plug? Here are the specs on the AR51 Shorty Spark Plug: No Resistor: No Electrode Tip Material: Chromium nickel alloy Electrode Core Material: Copper Insulator Type: Projected Spark Plug Thread Size: 14mm Spark Plug Reach: 0.750 in. Spark Plug Seat Style: Gasket Wrench Diameter: 13/16 in. Ground Strap Quantity: One From what I've read online the last digit is the heat range, so I'm assuming 1, so it's a fairly cold plug. For anyone who does not know the car it's an NA big block chevy, high compression running 112 octane. I don't have many more details than that as the motor is effectively the same as when I bought it turn key. The reason I am happy with the AR51s are that they work well, and they are cheap. Something similar would be ideal. Quote Link to comment Share on other sites More sharing options...
BuckeyeROC Posted June 17, 2019 Report Share Posted June 17, 2019 Would this chart help? Edit: Hotlink failed, so the link is here: https://www.sparkplugs.com/Data/uploads/Charts/NGK_Plug_Chart_1.jpg Quote Link to comment Share on other sites More sharing options...
BuckeyeROC Posted June 17, 2019 Report Share Posted June 17, 2019 Also: https://www.sparkplug-crossreference.com/convert/autolite/AR51 Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted June 17, 2019 Author Report Share Posted June 17, 2019 Also: https://www.sparkplug-crossreference.com/convert/autolite/AR51 I saw that while I was googling around. I figured those would all be direct replacement similar (non-resistor) plugs. I'll scope through some of them and see if any of them are resistor plugs. Thanks. Quote Link to comment Share on other sites More sharing options...
BuckeyeROC Posted June 17, 2019 Report Share Posted June 17, 2019 I saw that while I was googling around. I figured those would all be direct replacement similar (non-resistor) plugs. I'll scope through some of them and see if any of them are resistor plugs. Thanks. Looks like my first link is a bust, they don't like traffic to their site I guess. Google "ngk chart" and there are a few images of charts that break down NGK's part numbering system based on specs. Quote Link to comment Share on other sites More sharing options...
Geeto67 Posted June 17, 2019 Report Share Posted June 17, 2019 Is any part of the FI using radio or other transmission frequency to operate? Maybe Bluetooth or wifi to connect to the controller? The primary purpose of resistor plugs, caps, et al is to reduce radio interference from the ignition system. Anybody who has ridden in a 50's Chevy missing it's radio shield can tell you about hearing the engine through the radio. You can get resistor caps too but I think those are just shielded rather than having an actual higher resistance. The only other thing I can think of is that it wants a specific resistor plug to track misfires. If that is the csn you can just add a resistor inline to the plug wire and while it won't tell you if your candle is out, it will read normally. Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted June 17, 2019 Author Report Share Posted June 17, 2019 Is any part of the FI using radio or other transmission frequency to operate? Maybe Bluetooth or wifi to connect to the controller? The primary purpose of resistor plugs, caps, et al is to reduce radio interference from the ignition system. Anybody who has ridden in a 50's Chevy missing it's radio shield can tell you about hearing the engine through the radio. You can get resistor caps too but I think those are just shielded rather than having an actual higher resistance. The only other thing I can think of is that it wants a specific resistor plug to track misfires. If that is the csn you can just add a resistor inline to the plug wire and while it won't tell you if your candle is out, it will read normally. No, nothing is using radio waves for signaling, everything is wired. I went back through the instructions and I don't see resistor plugs as a requirement. I have watched a lot of YouTube videos as well and I may have seen it somewhere in there. I assumed they were simply trying to eliminate as much interference as possible. It does not list any specific plug in the installation instructions. I'll have to do some more research and see if my brain is making this all up. It was pretty late last time I was looking through the instructions and videos. Thanks everyone. Quote Link to comment Share on other sites More sharing options...
Cordell Posted June 18, 2019 Report Share Posted June 18, 2019 The resistor is just there as a precaution to help make sure there is no interference, voltage spikes and RFI are just not good with electronics. Look at these. They are a heat range 2, might be a good starting point. https://www.summitracing.com/parts/atl-4062/ Edit: a little more research and it looks like an AR51 is actually a heat range 3 So try this. https://www.summitracing.com/parts/atl-63/ Quote Link to comment Share on other sites More sharing options...
craig71188 Posted June 18, 2019 Report Share Posted June 18, 2019 The resistor is just there as a precaution to help make sure there is no interference, voltage spikes and RFI are just not good with electronics. Also, are you running solid core or resistor plug wires (If not coil on plug)? Solid core wire can also cause interference. Resistance wire sets are also run for the above reasons. Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted June 18, 2019 Author Report Share Posted June 18, 2019 The resistor is just there as a precaution to help make sure there is no interference, voltage spikes and RFI are just not good with electronics. Look at these. They are a heat range 2, might be a good starting point. https://www.summitracing.com/parts/atl-4062/ Edit: a little more research and it looks like an AR51 is actually a heat range 3 So try this. https://www.summitracing.com/parts/atl-63/ COOL! Thanks! Also, are you running solid core or resistor plug wires (If not coil on plug)? Solid core wire can also cause interference. Resistance wire sets are also run for the above reasons. Other good points. Not coil on plug. I believe it is an older MSD Pro-Billet Distributor. New plug wires seems reasonable for this project. Thanks! Quote Link to comment Share on other sites More sharing options...
Richard Cranium Posted June 20, 2019 Author Report Share Posted June 20, 2019 Based on Scott finding out the heat range is 3 for these. It looks like I'll probably go with the AR3924 Shorty Spark Plug: No Resistor: Yes Manufacturer Heat Range: 3 Electrode Tip Material: Chromium nickel alloy Electrode Core Material: Copper Insulator Type: Projected Spark Plug Thread Size: 14mm Spark Plug Reach: 0.750 in. Spark Plug Seat Style: Gasket Wrench Diameter: 5/8 in. Ground Strap Quantity: One Looks like the only difference is the wrench diameter size changes from 13/16 to 5/8. I don't think that change will be significant. Thanks again for the help folks. Quote Link to comment Share on other sites More sharing options...
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