plug selection

[oldtrux]

hi all,i,m hoping someone can school me on spark plug selection!i have a 283 4 bbl with hei.when i got it it had ac45 plugs in it(points dizzy).just wondering what folks are running for plugs.do i stay away from resistor plugs?i've heard good things about ngk plugs gapped to 40 or 45.would like to hear your opinions!thx

[Marv D]

FIRST you need to check and see which heads is on the motor. Just because you can physically screw a taperseat plug into an old head intended for the large gasketed plug... Don't mean it's a good idea.

The very early HEI took a plug with 0.060" gap,, then the very next year ((69 or 70 I think) the HEI coils became a bit hotter and the plug gap dropped to 0.045.
The thing to keep in mind is cylinder pressure (compression) is resistance to the spark jumping the gap,, more compression requires a tighter gap, and hotter coil. and cylinder temperature requires a plug that doesn't overheat,, nor doesn't run so cold that it fouls

Yes it is a balancing act.

If you don't know the true MEASURED static compression (calculated from measured chambers and deck clearance / gasket / valve reliefs,, do a compression test and at least we can get an idea if this is a factory 9.5:1 283 that is still donning the 0.015" steel shim head gasket and tiny combustion chambers,,,,, or if it has been a backyard build of mix and match with barely 8:1 compression (also cam will have a profound effect on cranking cylinder pressure but the psi will give us a very general idea)

THEN it's just a matter of identifying which type of plug the head is SUPPOSED to have (13/16 gasketed plug,, 5/8" gasketed plug, or a taper seat plug) , and then picking a projected tip / retracted tip plug to be sure you don't cause mechanical contact with the piston or valves,,, THEN you can pick a heat range that will work with the compression / cylinder temps. See and you didn't think there was any rocket science in just picking a stupid spark plug LOL.

Really it's not all that bad, but honestly every one of those points mentioned can present valid concerns.

FIRST is to verify the plug seat type. (the head casting number will usually do) Once you ID the heads and which base plug fits the head, then the rest can be approximated and a good starting point of a 'typical' heat range like the
"44" in Autolite,
a 12 series in Champion,
a 3 or 4 heat range in Delco

My personal preference is NGK, but the heat ranges can be confusing. I have a full plug x-reference chart]on the server in .xls format (click link) you can download. It's a few years old but has more information then you want to look at I'm sure.


So pick your poison and you can cross it to whatever brand you like.

[oldtrux]

thanks for the response marv d,the 283 has the original p/pack heads.the compression would be the stock 9.5:1.the cam was upgraded to mellings mtc 1
nothing crazy.dui hei distributor.i was thinking ngk xr5 but i'm unsure about the resistor part?your right...nothins easy lol.thanks so much for your help...dan

[Tazimafied]

I have been using E3's with good results.
'03 Monte Carlo.........3.5L
'00 Grand Cherokee...4L
'76 Blazer.................350ci HEI

Recently checked the plugs on the Blazer when my control module burnt to a crisp(never buy an Accell distro. They think silicone grease makes a good thermal compound) and the center electrodes were still in excellent shape after two years.