Your spark plug poll reminded me of a question I had been meaning to ask...
I have AC delco I think 43XLS plugs in my 68 L36. The owners manual recommends a 43 something plug and the ones I use are the present day equivalent. I have seen others recommend a 44 or 45 instead. Is that colder or hotter? That's really not my question. My question is, what type of performance difference should I look for in changing from a 43 to a 45 plug? Any difference in idle? hp? cold or hot starting? life of plug? What difference will it make? MJ

 

Spark plugs not only ignite the spark in your engine, but they also control, to some extent, the temperature of the combustion chamber. Spark plugs conduct the heat out of the chamber; how well they do this determines their heat range. With a highly efficient and/or high compression setup, you would run a lower heat range (aka colder plug) than a similar but lower compression/less efficient setup. My stock '76 L-48 I believe took an AC Delco RC45(TS?) plug. The 5 in that part number designates the heat range; a 4 is colder and a 6 is hotter. (The other parts are the size, taper, tip length). If you run too warm a plug, you will increase detonation and I believe you can even burn the tip off, and a red hot piece of metal flying around in your cylinder spells trouble. Too cold a plug will foul out - or load up with deposits (by being too cold to burn them off), and will eventually misfire and cause a rough idle and less power. You should use the plug the manufacturer calls for with your specific motor, unless you heavily modify it. Increasing the efficiency and/or compression, or adding boost or nitrous may call for a colder plug.

There is a good tutorial on this subject I believe on NGK's website, look around at the plug manufacturers websites for more info.

Rob

Try this info, it's a little more accurate than mine ;) http://www.babcox.com/editorial/cm/cm59910.htm


[Modified by robzr, 5:10 PM 8/10/2001]