Spark Plugs

[340Dart]

I am going to change the plugs. I noticed that the early 340's used RN9Y. Now they list the plug as RN12Y which is hotter. I have the Edelbrock heads so I was using RC12YC. I was going to go with the Autolites which would be 3924. Do I get those or do I get 3923's. I am running 10.2 compression if that matters. Thanks for any help.

Fred B

 

[Longgone]

I use the 3923`s or RN9Y in my stock 340. You can still get the RN9Y`s if you `d like ,you just have to order them by their # and not application. I like the Autolites a little better, they seem to have longer lives under more extreme conditions.

 

[bobs340dartsport]

I cannot understand why the newer books list RN12YC plugs for a 340, an engine with that much compression should use a cooler plug RN9YC.

RN12YC's are for an engine with lower compression 9:1 like a 318/2bbl.

I had the same issue with Champion Platnium Plus plugs I bought for my engine, the ones listed for car are the hotter plugs.

I have used the champion RN9YC, but actually prefer the Accel 114 u-groove plugs I used last season.

bob

 

['64 Cuda]

Wouldn't you want a bit hotter plug with the aluminum heads? Do they pull the heat out of the plug faster or is my thinking all screwed up? I know the 12's are what Edelbrock recommends, but we all know that every engine is different.

 

[dgc333]

You want to use the hotest plug that does not cause detonation issues. I have 10.6:1 compression in my 360 and I run 5224 or 3924 Autolite plugs which are equivalent to the Champion 12 heat range.

 

[Bigdummy]

what about NGK 5671-A7,6,5

 

[340srule]

Yes,3923's are the plugs you want to run i use them in my 416 stroker with Edelbrock heads 10.9 to 1 comp... i would'nt even run Champions in a lawn mower..