I have an 87 prelude Si. The engine is tired. It is border line to pass emissions. What spark plug would you recommend? Do they all burn the same? Does it matter what kind of conductor it has? Does it make any difference widening or shortening the gap for a tired engine? Tired in this case means compression that is below the minimum required.

~Rob

 

If you want to drop the coin NGK Iridiums are the best you can buy IMO. But they are also $8.00 a plug, I dont think for your car it would be worth it. I cant remember which ones are cheaper the NGK platinums or coppers, either way pretty much any "new" plug will work. Better plugs usually last longer too.

Spark-plugs do have different heat ranges but unless your car is modified I suggest just getting regular replacement ones. As for plug gap, I dont see any seriously noticeable advantage you would get by going over or under spec. Just do what the OEM manual says and it should work as well as its going to.