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My question is; how do you select your spark plug heat range? I have a 648" BBC with a set of 14 degree heads, and all of the bells and whistles, compression is going to be about 15:1 this year and it is in a pulling truck. I have been currently been runnig an Autolite AR3910, but I think it is pretty cold for my application. What do you guys think?
 

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My question is; how do you select your spark plug heat range? I have a 648" BBC with a set of 14 degree heads, and all of the bells and whistles, compression is going to be about 15:1 this year and it is in a pulling truck. I have been currently been runnig an Autolite AR3910, but I think it is pretty cold for my application. What do you guys think?
The AR3910 should be the correct heat range. Personally I would prefer the NGK R5672A-9 which is easier to read than the Autolite plug. The Autolite plug is a very good plug for running nitrous once you got your tune up right. But because it has a thicker ground strap it's harder to read.
Also the NGK with the thinner ground strap you can watch and if the strap mental starts fuzzing (burning) you know your on the edge of to much combustion heat. The thicker Autolite strap will not read that warning.
You can try a #8 heat range and see how it does. If you have to cold of a plug in the engine it will read like it's fat, but could actually be lean. Always run as hot a plug as you can get away with.
My thought's anyway..............Blessing................Ron.
 

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I just noticed that your plug is different (R5672A-9) than mine (Big Chief 18 degree) R5671A-9 (#9 heat range) so make sure you've got the right plug.

Blessings.........Ron.
 

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Discussion Starter #4
Thanks for your reply's. I did some cross referencing and we are using the same heat range plugs. The difference between yours and mine are you plug should use a 13/16" socket and it is a standard tip. Mine uses a 5/8" socket and has a projected tip. I do not run any form of nitrous that you are refering to in your first post, my engine is N/A.
 
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