Z28 Boy

i did a search on this, but there wasnt anything that was general...all specific to certain engines and setups.

can anyone give me an idea of how to choose a plug's heat range and what gap to use? what changes do these parameters make to the performance of the engine? what other ignition upgrades are required to use different "settings"? in my experience, "advanced" plug selection and gapping is a pretty overlooked aspect of tuning a car.

right now, i use AC Delco R44-LTSes. i have all MSD ignition (including a 6-AL).

this is definitely the type of info that a single web page could answer, so if anyone has any good links with this info, let us know.

thanks a lot...

-brian

rustybluebird

this site has some good general info on plugs
Ngk

Ukraine Train

i co-op for autolite so i think i can field some questions

factors that will determine what heat range to run are mainly compression, cooling and timing. an increase of approximately one full point of compression will require a one heat range colder plug. more timing will also require a colder plug. an aluminum head will dissipate heat faster than an iron one so you can run higher compression with aluminum without preigniting. when i built up my motor, i started with a plug two heat ranges colder than factory and ran it for a while. those plugs fouled out so i moved up to one heat range colder than stock and stopped there because i was getting a nice tan color on the ceramic. if you get bright white or the plug looked like it has melted then you're preigniting and are risking serious engine damage. hence the reason for starting with a cold plug, carbon fouling wont harm the engine

as far as gap goes, a larger than stock gap could smooth out your idle some but doesn't do much at higher RPMs. a larger gap will increase the voltage required to spark due to the longer distance and that will make your plugs, cap and rotor wear faster. one of the techs at work went to one of the big nascar team's garage for testing and he said their plugs were only running 9kV, indicating that their gaps are small. for comparison, a factory ford DIS system runs at about 20kV. the best plugs to use are finewire double platinums. the platinum pretty much illiminates wear (and is NOT a performance enhancement like many people think) and the finewire (referring to the diameter of the center electrode being small) decreases required voltage. i have heard, though, that you shouldn't use platinum plugs with MSD ignition, not sure on the details with that.

which brings me to another point. factory igniton coils, wires, and control modules are fully capable of 6000rpm+ and you dont need an MSD box or upgraded coil or module unless you're turning above that. in fact, because the msd box has to support such high RPMs, it charges and discharges much faster than a factory coil which means less energy output in the spark compared to a factory coil until you hit high RPMs where the factory coil doesnt have enough time to charge/discharge. less energy doesn't necessarily hurt anything, it just means that at low RPMs the MSD box is doing absolutely nothing for you