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Old 05-13-2012, 06:55 PM
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Plug heat range question

Having a hard time telling which one is the colder plug

AR3924 which is a 5 heat range

Or a NGK R5671A-7 Which is a 7 heat range

Now the way this works is NGK the higher the number the colder the plug

Autolite the higher the number the hotter the plug..

Yeah i'm extremely confused maybe somebody can sort this out for me and let me know which one is the COLDER plug..

Thanks guys appreciate it

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Old 06-11-2012, 05:39 AM
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Well here is some homework for you buddy. Lots of smoke and mirrors in the numbers for sure. No such thing as a "quick " answers.
The AR 3924 is equivalent to an NGK FR5 which is a hotter plug than a NGK R5671A-7 (NGK high numbers= colder plug. )
So using the info from the chart (link) the colder plug of the 2 you have listed is the NGK R5671A-7.

Personally i use the NGK plugs in my 347. They have the correct colour up after 1000 new miles so i will stick with them. The gaps i have found only open marginally after a lot of service. I cant remember ever having a bad one.
Cheers from downunda
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