spark plugs

i have ngk's on my 1995 5.7 tbi but i want to go back to ac delcos but their heat rating is a 3 and the ngks is a 5 will this better or harm my mpg

as for heat range of a plug it is a measurement at witch a plug begins to break down depending on the spark voltage 40.000 --80.000 v is what you need to look at to determine heat range / regardless of heat range you cant make gas burn hotter or cooler and to get the best gas mileage from a spark plug match voltage to plug /as for what are asking I don't think for a stock motor normal driving I don't beleave it will make much difference in your gas mileage if any

I would suggest to all posters here to google spark plug heat ranges for a better understanding of what determines a plugs heat range and how that relates to engine and combustion chamber design..

i have ngk's on my 1995 5.7 tbi but i want to go back to ac delcos but their heat rating is a 3 and the ngks is a 5 will this better or harm my mpg


I would use the ac delco irridium plugs that are the OEM recommended plug. changing heat ranges is only done to attempt to overcome a worn engine problem.

these irridium plugs work much better than plats. they can take much higher heat .last much longer.. only problem is if you mess with the gap you will break the plug tips.