I am going to run either autolite or champion spark plugs in my 340. The compression is right around 9.5:1 with iron J heads. What would be a good heat range to use with 93 octane pump gas. My ignition is MSD 6al with blaster 2 coil.
What heat range plug should I use for my 340???
- Thread starter duster360
- Start date
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CPMotorworks
Well-Known Member
NGK 7 would be my choice to start.
EL5DEMON340
Well-Known Member
NGK would be my choice also v power.
fishy68
Tyr Fryr's Inc.
I've had good luck with NGK V-power too. Your on the line for a 6 or 7 heat range. Start with a 7 and see how it looks after a few runs. May be fine or you may need to step up to a 6. My 408 is 9.8 to 2 compression and likes a 7
Would one of you mind helping me with the part number I would need at my local Advance Auto Parts? When I looked up the plugs for my engine it called for a 2635 part # and that was a plug with a 4 heat range. What # for the 6 - 7 heat range plugs?
CPMotorworks
Well-Known Member
R5671A-7 Stock #4091 is a 3/4" reach, gasketed, 5/8 hex, #7 heat range
Found it. Thanks Pete.
connerray
Well-Known Member
With a good spark, I don't see any problem with 40-45 gap.
fishy68
Tyr Fryr's Inc.
I've found some engines like a wider gap and some make no difference, or even slow down but it never hurts to try opening it up and see if it likes it. If it slows down close it back up .005" at a time until it peaks.
Rude72*
Well-Known Member
Hey fishy… I have a ‘72 Duster (built 340) with 11:1 compression. Do you think the NGK 7 (V-power) would be a good choice?
Thank you!
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