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Thread: Question about plug heat range.

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    Default Question about plug heat range.

    So I have been chasing ghosts for a time now. Managed to improve the performance of my car over 40 horsepower to the rear wheels. Recently it came to my attention that the plug heat range could have a significant effect on engine performance and potentially the carburetor adjustments.

    Case in point, my plugs were cold fouling and the car was running rich. The plugs smelled like gas when I pulled them to check them. I cleaned them up and put them back in and they seem to improve that adjustability of the four corner idle screws and improve performance. However, over time the rich condition seemed to return. Checking I found I had NGK level 6 plugs in the car. I changed those for AC Delco R45 and the same results, they were fine for a short period of time then everything went bad as they fouled. I did notice that when I adjusted the four corner adjusters lean, engine operating operating temperature seemed to rise. The change was about 15°. I also noticed I had seen the condition deteriorate over time when operating the engine say continuously for an hour. So I changed the floats out to. They had been sitting dry for several years prior to firing the car up. Settling down with the cleaned NGK heat level 6 plugs and new floats I was able to adjust the four corner screws inward from 5 and 1/4 turns from the seat to about 3 and 3/4 turns. That is when I noticed the engine temperature climb about 15°. I backed the adjustment screws out about 1/4 of a turn and the engine cooled back down.

    I went and bought a set of R44 plugs and put them in. I was able to adjust the four corner screws inward to about 2 3/4 turns from seated. The plugs read really good right now but the car is hard to start. I have the timing set at 18° initial and 36° full advanced with a very short curve (light springs). So the question is there really a correlation between the adjustment screws and the plug heat range? I have about 50 miles on this plug.

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    Last edited by wrp; 04-17-2017 at 06:40 PM.

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