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Junior Charter Member
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Discussion Starter #1
I just picked up a used Challenge Car and was going through a few things. The car came with a fresh box of Autolite 3924's. However when I pulled the plugs from the car they were Autolite double platinum APP 25's, which have a much shorter threaded length. What is the right plug?
 

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Pro FFR Builder and Moderator
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14,662 Posts
3924's. The 25's are for stock iron 5.0 heads.
 

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3,235 Posts
So, I look up the Autolite 3924's and there are at least 4 different types.

From Amazon:

Copper $1.99

Iridium XP $5.63

Double Platinum $4.69

Platinum $2.99

Recommendations?

Thanks, George
 

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Premium Member
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1,266 Posts
Boils down to what you want to pay and what metal you think is the best. I run the basic copper plug. I tried all kinds of different plugs, pre-Trick Flow heads, and came to the conclusion that basic plugs are fine.
 

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Me too. Regular old copper ones. Cheap and work well.
 
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