How much will this affect mileage and drivability? Especially on a stock CA18?
you might foul them if you don’t need them. for a stock CA18, don’t bother.
for example: if you had turbo back exhaust, T28 and running 14psi, then you might want to go one heat range colder.
what sort of symptoms would call for a colder or warmer plug?
Usually higher boost or higher compression situations will call for a colder plug.
If you are fouling plugs go hotter.
If you are missing at high rev’s or high boost go colder.
Stock heat range is a 5. Turbo engines is a 6. Most people with upped boost and exhasut run a 7.
will an engine act differently if a different plug is needed? What should be looked for?
NGK BCPR6EIX-11 number 6 is the heat range…
http://www.ngk.com/results_app.asp?AAIA=1212444 u can find these at canadian tire or part source…