I am currently running an IK27 from Denso in a AFR 210 headed LT1. I have a nitrous setup that is going to force me to a colder plug. The shop that did my dyno work are not in favor of the iridium center electrode and directed me to a autolite 3923 or 3924. These look to be 2 and 3 steps hotter and not at all what I want. The Denso that is two steps colder also had an iridium center electrode and cost 18.90 apiece. I don't mind the cost if it is what I need but can anyone suggest an alternative with a resistor or convince me I don't need resistor plugs with the BigStuff 3 computer?

TIA

Rick

 

I would not run the 3923 or 3924 in a NOS application, they work great for mild NA.

I believe the coldest resistor plug from autolite for your application is the 3922.

The 3911 and 3910 are very cold non resistor plugs, they work well in all out effort.

Add AR to the plug number to get racing plugs with cutback ground electrodes

 

The Autolite 3910 is the suggested starting heat range for the AFR's. I had it in my head that I needed resistor plugs and sought them out. I have read at sparkplugs.com that the iridium has not been a problem with nitrous and I can go the two steps colder. These plugs are pretty well suited to racing with a rounded end and concave underside, to unshroud the spark kernel, on the ground strap.

Rick

 

Just get a regular set of cold plugs and put them in. There is not a big secret to it. It's not like ya will gain a .1ET by changing plugs.

 

Are you saying I do not need resistor plugs? I guess there is one way to find out. I'm not attached to exotic materials or high price tags.

Thanks,

Rick

 

 

I don't know about the BS3, but non-resistor plugs do not interfere with my MoTeC ECU. I run a Champion S57YC with a 300-shot.

 

Ya don't need them as long as ya got good resistor wires.

 

I’d bet that you wouldn’t see as many if at all of the iridium in the more serious competition engines if it wasn’t for the contingency money/sponsorship that they are throwing around to get their name out there, hell, look at engine masters…

You need the resistance somewhere, but not necessarily everywhere. I’ve run non resistor autolites in my 3rd gen just because the autolites were one of the few common plugs that I could get in that heat range (AR12) and I don’t trust autolite resistor plugs (try measuring resistance across them and pressing on the electrodes, you’ll find that a good percentage of them are loose and change resisance and will even go totally open in some positions). No problems with a factory style ECM and a hot ignition…

 

Just FYI (plug trivia), it doesn't always work to measure resistance of a plug with an ohm meter cause some plugs have a resistor with a semiconductor type pellet which actually changes resistance in use and others have a fired-in ceramic slurry type resistor which you can actually measure with the ohm meter. Just depends on how it is constructed. And don't forget that when 20,000 volts is going thru the plug, the resistances from internal parts and oxidation are negligible when compared to the pissy 9 volts or whatever the DMM is trying to put through the circuit - so, while the resistance might be hard to measure, it is probably still a good plug. For instance, NGKs you can measure, Champions you can't - some of the others I haven't tried because we don't use them at work, but the fired in suppressor plugs are more common. A lot of the manufacturers make plugs for several brands, so you don't always know what you got (some automakers use plugs made in China...). Typically, the reject rate of bad plugs off the assembly line is about 3-6 parts per million - they are very dependable parts. The production lines for them are completely automated.

 

Oh, I wasn’t implying that you can tell anything by the actual resistance value of the plug, but that you’ll find that different plugs consitently follow patterns, and that the autolite resistor plugs are consistenly inconsistent and I’ve found a good percentage of them with loose center electrodes, and FWIW, they aren’t always a problem in the car, but I have found that if you have a miss caused by a plug, going through and replacing the inconsistent ones has always gotten rid of it for me (and usually it takes 10-11 autolite resistor plugs to find 8 consistent ones). FWIW, Autolite seems to have the hardest insulators out of all of them which is good and bad, good in that nothing soaks into them and they are more likely to clean themselves off then any of the others if you foul them, but bad in that they are very easy to crack and cause misfires, a little too much sideways pressure on the socket, drop the box… NGK seem to be the other end of the scale, softest insuators.

As far as different manufacturers… take a look at the AC Delco plugs coming out of the boxes… I’ve had plugs with exactly the same PN (R43TRS or something like that) come out of the boxes looking completely different, some have “old school” insulators and logos (the same as the original plugs I found in my ‘83TA) and some have newer, longer design insulators, they actually look a lot like the Autolite resistor plugs. I’ve never had a problem with the old school ones, they seem to last forever also, but the newer design seem to only last a fraction as long… I know I had a set that were in my truck for 5K miles and started misfiring.

Oh, back to fouling and cleaning up… 2 nights ago we had our first really cold night and I realized that I didn’t have any antifreeze in the radiator of the formula, so I siphoned what I could off, dumped some antifreeze in it and went to start it. Initially the battery was dead, and at 22*F, the engine barely cranking, a tank full of summer gas, 77pph injectors, a half assed tune that was never tuned for anything colder then 60*F, and worst of all, super cold, AR12 plugs… that I fouled the plugs and that will be the end of it. As a last ditch attempt I ran jumper cables from the truck and no ****, it started and seemed to clear it self up as it warmed up (to get the thermostat to open and circulate the coolant, can’t drive it because it’s got a blown up transmission in it.)

 

I checked with the Champion rep about my suspicions and he confirmed that, although Autolite makes some of their own plugs, Torch is also making some of them (can you say Chinese quality?) AC Delco is making some of their own plugs, but Champion is also making some for them. Hope this helps solve part of the mystery.