Spark plug help NGK Plugs

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SRT_DSTRHOLC

SRT_DSTRHOLC

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Hi guys, I am trying to find the hottest plug that NGK makes for some Magnum style closed chambered RHS Indy heads. I currently run FR5s with gas, but I am switching to E85 and was told by Mark Sullens that I need a hotter plug. I believe I may have found the hottest plug, FR2B-D. It has the same reach and thread as the Fr5's but I wanted to ask for some more help before I buy them. Thanks!
 
I think your headed in the wrong direction. Mark recommended a 7 heat range for me. Like a NGK 5671a-7 or autolite ar3935.
Fr5 is a 5 heat range. I used to run these.
 
Plugs are to be hotter for e85 is what mark said. I currently run FR5 and FR4 is the hottest
 
According to google on the NGK site the lower the # the hotter the plug.
FR4 is hotter than FR5!!
 
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