Spark plug?

[partsman1965]

I need input on recommended spark plug for my 340. I'm running forged flat tops with J heads with 2.02 intakes. 484 lift MP purple shaft hydraulic cam with Torker 340 intake and Holley Street Avenger 780 CFM vacuum secondaries. Header and 2 1/2 exhaust through flow masters.
Chrome box ignition,stock dizzy and Mallory coil. Any info would be great.

 

[69_340_GTS]

RN12YC Champions should work just great.

 

[jimjimjimmy]

rc12yc champion . or the same in whatever brand you choose .

 

[stroked340]

Autolite 3924's...

 

[partsman1965]

Thanks everyone!

 

[Marcohotrod]

Whoa, we need more info, forged flattops is not enough info. compression ratio or deck height? 1968-71 340 was 10:1 and chrysler used n9y, 1972-3 was 8:1 and used n12y

 

[partsman1965]

zero/flush deck height. felpro head gaskets. so estimated CR is about 9.5 - 10.0? It has rn11yc in it now which were in it when I got it. Ran great with prior cam which was .454 lift. Now with .484 cam it seems to run rich with no carb adjustments made.

 

[Marcohotrod]

you are around 9.7:1, and I don't have a radio so I run non resistor plugs, = n11yc or 54 autolite. bigger cam=less vacuum=lower power valve, may be why it is rich

 

[RustyRatRod]

The 12 series Champions are a perfect starting point.

 

[partsman1965]

great info

 

[kiss]

Aren't Champion spark plugs made in China now?
NGK GR5 is what I used because I thought that was the case...

 

[aaronk785]

I like ngk. The last set of champions I bought were horrible. The center electrode wasn't even close to center on 3 of them. Lined up about half way off center with the ground strap so no more for me. I have used autolite also with good results.