Spark Plug Help....
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Joined: Oct 2013
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Spark Plug Help....
I've looked everywhere to find the correct answer with no luck. So hopefully the vast knowledge on this forum can save me. I need to know what plugs to run in my 68? The deal is though, I have a 402 out of a 1972 Monte Carlo in the car with a set of closed chamber cast number 215 heads which are 101cc out of a 1968 396. So do I use the stock R43N plugs that are for the 67 to 69 396, or do run the R44TS plugs that were for the 1972 402s? I also have a MSD Pro Billet distributor on it if that makes a difference in plug gaps or do I just stick with the standard 0.035 gap? Thanks ahead of time guys. So the questions are, what plug numbers at what gap? The car came to me with R44XLS plugs in it.
In the Staging Lanes
Joined: Jul 2013
Posts: 97
From: Greenville, SC
You have to know a little bit about spark plugs first.
R is for resistor
43 is the heat range
N is the tip design, in this case a four ground electrode
The shorter the trip you drive, the higher the heat range you will need to burn the fuel more efficiently. So, the higher the middle numbers are (43 in this case) the higher the heat range.
If it were my car I'd run the R43N plugs and see how they perform. After driving for a hundred miles or more, I'd take one out and see how the splash looks on the insulator (the carbon deposits on the white ceramic). That is one of the best indicators of having the correct plug heat range. If the ceramic looks reasonably clean and not dark, you are in the correct range for the engine. If it is dark you will need to go to a higher number heat range.
That plug is set at .035 gap. High gap plugs are used in some engines with higher output coils that will jump that high gap. Like the HEI distributors of the 1970's and up. They also have lower compression usually and more clearance, so the "plug reach" won't hit the top of the piston.
Here's a diagram of AC plugs for you AC Spark Plug Heat Range - Bing Images
I hope that helps and doesn't confuse you any.
R is for resistor
43 is the heat range
N is the tip design, in this case a four ground electrode
The shorter the trip you drive, the higher the heat range you will need to burn the fuel more efficiently. So, the higher the middle numbers are (43 in this case) the higher the heat range.
If it were my car I'd run the R43N plugs and see how they perform. After driving for a hundred miles or more, I'd take one out and see how the splash looks on the insulator (the carbon deposits on the white ceramic). That is one of the best indicators of having the correct plug heat range. If the ceramic looks reasonably clean and not dark, you are in the correct range for the engine. If it is dark you will need to go to a higher number heat range.
That plug is set at .035 gap. High gap plugs are used in some engines with higher output coils that will jump that high gap. Like the HEI distributors of the 1970's and up. They also have lower compression usually and more clearance, so the "plug reach" won't hit the top of the piston.
Here's a diagram of AC plugs for you AC Spark Plug Heat Range - Bing Images
I hope that helps and doesn't confuse you any.
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QUICKB4C
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