Let's talk about spark plugs. I know there are a lot of opinions on what kind of spark plug to use in our old engines (351M, 400, 360, 390, 429, 460). I want to gain some real knowledge from you all. Trial and error knowledge. I read a very small article many years ago about this but can't really remember what it said.
First and most important question- What heat range of spark plug should we run? I know too high of a number results in pre-ignition. Too low of a number results in poor performance and sooting.
Second question- What is the manufacturer's recommended plug style? I don't imagine it a "platinum" series or nichel chrome plug. I would think a copper core is likely the choice.
I'm not looking to buy a high dollar performance plug for $25 each. I just want to get the best plug for my mildly built 351M daily drive.

 

A stock heat range plug in a stock engine is where to start with tuning. The engineers knew what they were doing. As performance modifications are performed, a colder plug is needed.

Personally I like NGK. If a hotter, or colder plug is needed, they make them in several steps on either side. And they are good quality. One thing to keep in mind is to take those spark plug cross reference charts with a grain of salt.

 

I used to run Motorcraft plugs. Never bought into the gimmick plugs. But a knowledgeable friend convinced me to try E3's. I'm very impressed with them.

 

I run champion in most everything because I always have , and they're hard to beat on the dyno. and the same thing that makes them better on the dyno ( losing metal off the electrode ) makes them better on old inefficient engines like we have in these classics. yes they have a little shorter lifespan but who cares for the amount of miles most of us put on a year.

But the reality is the difference between the best and worst plug is so insignificant it's really not important. . run whatever you like.

 

Yep, purdy much! I change mine a couple of times a year. It's just too easy and inexpensive.

 

Autolites copper heads last me 15-20K mi.

 

Motorcraft coppers here!

I have to say that I tried Splitfires in an old Mustang, and was impressed - they looked like Motorcrafts, with the ground electrodes split at the end.

 

One thing somebody pointed out on another board, a spark plug isn't really a super high-tech device, some electrodes, a copper wire, ceramic. How simple can you get? But different brands for whatever reason sometimes run noticeably different in a given engine. So it's worth experimenting a bit.

 

I wasn't looking for any particular brand of plug. I was wordering about the manufacturer's heat range number is for a stock engine. The more I read about the nitty gritty about spark plugs, the more questions I have. The higher the number the hotter the burn. The higher the compression ratio, the hotter plug requirements. Yet no where can I find a starting point. It also seems that most plug brands have their own numbering system. Which causes more confusion for me. Did Ford install all Autolite plugs from the factory in the 70s? When did the start using Motorcraft plugs? Autolite and Motorcraft both have different number system.

 

Ah. Some spark plug manufacturers have consolidated their lines. They claim one spark plug covers more than one heat range. And it's also confusing if you want to switch brands, because the cross-reference charts don't make a lot of sense if you dig into them. I wanted to try a colder plug than Autolite 45, but they don't make a 44. Now what? I can try to find NOS Champion's from back in the day, or maybe Autolite or Motorcraft, but they can get spendy. Starting to see why I like NGK? The reason to start with a stock plug is to get a baseline.

When I first got my Y-block, the plugs were fouled badly because I didn't know how to do a good tune-up or adjust and calibrate a carburetor. I installed a hotter plug. That isn't how it works. Basically the routine is get the ignition, ignition timing, and distributor curve straight, then tune the carburetor carefully for float height, jetting and power valve and the rest of it, and then inspect stock plugs carefully.

As someone mentioned in the older ignition systems they (factory) used fairly hot plugs, because the ignition systems (coils, points & condenser) weren't quite as hot as electronic ignition, and driving around town and idling tends to foul plugs. Kind of have to sneak up on timing, too much robs power, sneak up on fuel, too lean actually increases fuel consumption at some point, and too hot a plug cause detonation. Or pre-ignition, I forget. It's real destructive whatever it's called. Weigh how far you are from a stock engine and make a plan, start from the cold range plugs and work up in heat range. A too-cold heat range plug that fouls a bit in testing won't grenade your engine, but too hot of a plug might be real trouble. If going on a long highway trip in the summer, a step down or two colder heat range plug might be necessary.

Most manufacturers have a system with a higher number = hotter plug. NGK is the opposite.

 

Getting a complete understanding of spark plugs will probably be harder than finding Amelia Earhart or Jimmy Hoffa. It's a bit like finding the best engine oil or filter. You'll get plenty of opinions. What works the best in your 351M may not be the best for my 460.
Your first question is on heat range. I usually try to use the coolest plug that doesn't foul out. There are a lot of factors that will determine which is best. You may just have to start with what the manufacturer recommends and then go up or down from there. All of your circumstances will combine to determine the best. Try to learn how to "read" the plugs after they've been in the engine a while. An examination of the tips will tell how that cylinder is performing.
Your second question concerns plug style. Unless you do a lot of driving or have some condition that erodes electrodes, you won't need the platinums, iridiums, etc. The basic plugs will suffice for most people.
Some manufacturers have their own "line" of plugs. GM had AC; Ford had Autolite & Motorcraft. I thought that Ford started using Motorcraft around 1972, but these days I don't trust my memory as I once did.
The engine exhaust emission control information sticker on my engine's valve cover says that it should use Motorcraft ARF-42 spark plugs with a gap of .042-.046". As far as I know, that number plug is no longer being produced. Hence I must use something else. If you look at the plugs recommended for that engine at Rock Auto Parts you will see many possibilities. You're right; each brand has their own numbering system. Equivalence charts may not always be one to one. Electrodes are sometime different. Internal resistance is sometime different. Some plugs have their shells plated; others do not. Shell to insulator sealing differs.
The spark plug world seems to fit Churchill's comment about Russia; it's a riddle, wrapped in a mystery, inside an enigma. Best wishes for your study of it.