SPARK PLUG RECOMMENDATION FOR SCJ-A ALUMINUM HEADS

I have a 466 BBF with SCJ-A aluminum heads, 10.13 compression. This motor is not a race motor, but a daily driver in a Super Cab truck. I need to know what spark plugs to use with these heads. Autolites? NGK? Or??? Also, what heat range? From what I've read, it's recommended to use Motorcraft AGSP series of plugs, but I need to know exactly which specific plug #. To be honest, I don't know anything about spark plugs and which ones to use with aluminum heads vs iron heads, which is why I'm on here asking for suggestions. Thanks in advance for the advice.

I use NGK's because they have a shiney finish on them as opposed to a black oxide coating for the others....which makes plug reading much easier (especially if your eyes are not the greatest!!).
I use NGK #9 it is a moderately cold plug for nitrous use, but you can probably begin with a NGK #7 as it is a little hotter of a plug.

Since I'm not using nitrous or any other power adder and my motor isn't super high compression and I'm not racing it, am I understanding you correctly that I should use a hotter plug rather than a colder plug? What NGK plug would be too hot for my setup? Also, what's your thoughts about v-style plugs and platinum plugs? Are they a waste of money? Copper is the best conductor of electricity, right? So wouldn't a classic style Autolite (or another brand) copper plug be best? Educate me.

It depends on the rest of your ignition system components. Just going from memory (or lack thereof!! ), I think some ignition boxes such as MSD have some type of warning against using certain style of plugs/wires.

I have all MSD stuff. an NGK #5 is in the ballpark of what a "stock" plug would be. A #4 would be a little hotter still.
So on a scale it looks like this
Cold <---------10, 9, 8, medium <------7, 6, 5........4, 3, 2, 1-------> Hot

AR3924 Autolite has always worked well for that application.

Oh yea ... they are nickel plated not black oxide.

I'm using a MSD 6A ignition box, MSD Blaster II coil, FAST EZ EFI 1.0 throttle body fuel injection....So when you say the #5 plug is in the ballpark of a stock plug, would that be stock on an iron head? Aluminum disperses head better than iron, so should I be ok using a #4 plug? Would that be too hot for my setup?

Correct me if I'm wrong, but a hotter plug does a better job at igniting the fuel/air mixture and burns more completely, is that right? So what happens if I use a plug that's too hot?

I'll look through my MSD stuff and see if it gives any suggestions of plugs to stay away from.

Also, I want a resistor type plug, right? What does a resistor plug accomplish vs a non-resistor type plug? Does that have anything to do with electrical interference in the stereo system? I remember back when I was a kid listening to a tape deck in a car and you could hear a buzzing sound through the speakers that seemed to get worse when you revved the motor. Does this have anything to do with using a resistor vs non-resistor plug?

78 F150 wrote:I'm using a MSD 6A ignition box, MSD Blaster II coil, FAST EZ EFI 1.0 throttle body fuel injection....So when you say the #5 plug is in the ballpark of a stock plug, would that be stock on an iron head? Aluminum disperses head better than iron, so should I be ok using a #4 plug? Would that be too hot for my setup?

Correct me if I'm wrong, but a hotter plug does a better job at igniting the fuel/air mixture and burns more completely, is that right? So what happens if I use a plug that's too hot?

I'll look through my MSD stuff and see if it gives any suggestions of plugs to stay away from.

Also, I want a resistor type plug, right? What does a resistor plug accomplish vs a non-resistor type plug? Does that have anything to do with electrical interference in the stereo system? I remember back when I was a kid listening to a tape deck in a car and you could hear a buzzing sound through the speakers that seemed to get worse when you revved the motor. Does this have anything to do with using a resistor vs non-resistor plug?

Yes, a #5 plug would be very close to a stock iron head application. A #4 plug will work too, but keep an eye on things just to be safe. A hooter plug will ignite the mixture easier, but it can also cause pre-ignition / detonation if its too hot. Since its electrode is longer, it protrudes further into the chamber and holds heat at the tip longer than a colder plug.

I remember the same whining sound coming from the car speakers too when I was young!! Resistor plugs helped to cure that, but in this day and age of much better quality electronics, I don't know if its much of an issue anymore!!

Well I just reviewed my EFI instructions and it says to stay away from non-resistor plugs and solid core plug wires. So I guess that answers my question on resistor vs non-resistor plugs.

I do worry about pre-ignition, especially when towing my trailer. But I do have forged pistons, so that helps stand up to pre-ignition issues. So #5 or #4 plug....Hmm....Leaning toward #5 just to be safe. But maybe I can get away with a #4 plug because of the aluminum heads. Hmm, need to think about that one.

I know I have NGK plugs in now and will be changing them, but not sure exactly which plugs I have. Need to look into that, hopefully tomorrow if the weather holds off.

78 F150 wrote:Well I just reviewed my EFI instructions and it says to stay away from non-resistor plugs and solid core plug wires. So I guess that answers my question on resistor vs non-resistor plugs.

I do worry about pre-ignition, especially when towing my trailer. But I do have forged pistons, so that helps stand up to pre-ignition issues. So #5 or #4 plug....Hmm....Leaning toward #5 just to be safe. But maybe I can get away with a #4 plug because of the aluminum heads. Hmm, need to think about that one.

I know I have NGK plugs in now and will be changing them, but not sure exactly which plugs I have. Need to look into that, hopefully tomorrow if the weather holds off.

Your timing and the quality of gas will be big factors here!!

Timing is at 14* at idle, 30* all in by 3000; set up to work with my heads via recommendations by a BBF engine builder. I'm also using top quality pump gas; Conoco supreme 91 octane with no ethanol.

RM gave you the answer autolite 3924 .My 460 drag car uses them and my fe powered edelbrock headed street car uses the same 3924 plug .I gap mine at 0.40 sometimes 0.45 MSD ignition.

manofmerc wrote:RM gave you the answer autolite 3924 .My 460 drag car uses them and my fe powered edelbrock headed street car uses the same 3924 plug .I gap mine at 0.40 sometimes 0.45 MSD ignition.

There are 3 differences between the AR3924 and the standard 3924. They are both resistor plugs.
1. the standard is not nickel plated
2. the ground strap on the AR plug is cut-back to the center of the center electrode
3. the standard one costs about twice as much from most places; although it is available almost anywhere.

1. What does AR stand for; Autolite Racing? I noticed in a lot of the threads I've read through that guys who were using AR plugs had motors with higher compression than what I have and they were racing their vehicles.
2. Why are the ground straps on the two plugs different? Is there any benefit to having the ground strap cut back on the AR plug? Will it make a difference in how my motor performs?
3. Is it better to have nickel plated?
4.Do I want the standard plug or the AR plug?

78 F150 wrote:1. What does AR stand for; Autolite Racing? I noticed in a lot of the threads I've read through that guys who were using AR plugs had motors with higher compression than what I have and they were racing their vehicles.
2. Why are the ground straps on the two plugs different? Is there any benefit to having the ground strap cut back on the AR plug? Will it make a difference in how my motor performs?
3. Is it better to have nickel plated?
4.Do I want the standard plug or the AR plug?

Either one will work the same in your application ... the standard plug ground electrode will usually last longer before needing replacement.

Thanks for the info. I'll probably go with the standard plug due to longevity. So does nickel plated last longer than non-nickel plated? Does nickel plated produce a better/hotter spark?

78 F150 wrote:1. What does AR stand for;

 Assault Racer

78 F150 wrote:2. Why are the ground straps on the two plugs different? Is there any benefit to having the ground strap cut back on the AR plug?

 Better concealment  

78 F150 wrote:3. Is it better to have nickel plated?

if you sweat a lot.

78 F150 wrote:4.Do I want the standard plug or the AR plug?

It depends if you want a typical or a scary looking plug.

So I got the heads off the truck today as I need to have steel inserts put in the spark plug holes because one of the holes is starting to strip out. So I took a look at the plugs I've been using and they are NGK R V-Power UR4 plugs. There's also this number on the plug: K4YG. So can someone tell me what heat range of plugs I have? One of you guys mentioned heat range 5 was about a stock heat range, with a 4 being a little hotter plug. Is this a heat range 4? Is that was UR4 stands for? Are these good plugs to run with my heads, or not?

78 F150 wrote:So I got the heads off the truck today as I need to have steel inserts put in the spark plug holes because one of the holes is starting to strip out. So I took a look at the plugs I've been using and they are NGK R  V-Power UR4 plugs. There's also this number on the plug: K4YG. So can someone tell me what heat range of plugs I have? One of you guys mentioned heat range 5 was about a stock heat range, with a 4 being a little hotter plug. Is this a heat range 4? Is that was UR4 stands for? Are these good plugs to run with my heads, or not?

If the plugs you are using with the aluminum SCJA heads are the "UR4"  then they are completely wrong; the thread reach is wrong, the heat range is wrong and the seat type is wrong.

Good to know. So I'll be looking to get the 3924 plug as you suggested....

A few questions....with the things you mentioned that were wrong with the plugs I was using, what was affected by using these plugs?

1) You mentioned the thread reach was wrong, which I assume you meant it was too short and didn't reach far enough into the head? If it's too short, was it not burning the air/fuel mixture very well? Can you clarify this issue?
2) You also mentioned the heat range was wrong. What heat range are these plugs?
3) What seat type do these plugs have vs the 3924?

Sweet Jesus man, buy the f'n Autolite plugs already!

Those heads use 3/4" thread reach, gasketed seat spark plugs. The heat range is determined by the rest of the engine specs and how it is to be used.

You may now need to "chase" the spark plug hole threads as those shorter reach spark plugs have probably allowed the bottom third of the threads to become hindered with carbon and other combustion trash.

Jasonf--I will be buying the 3924's as I stated earlier. But in the mean time I'm trying to educate myself on spark plugs by asking questions so I don't have this issue again down the road. Not sure about you, but I like to know WHY I'm doing something, that way I can make educated decisions. Relax man!!!

Rmcomprandy--One of the spark plug holes have already started stripping out because I have a tendency to over tighten things. So I'm going to have steel inserts put in all the spark plug holes to prevent this from happening again down the road. I consider this "preventative maintenance". This is why I pulled the heads in the first place. Actually, I am in the process of swapping intakes from a dual plane to a single plane that will work better with my TB EFI system, and while I had the intake off I figured this was a perfect time to pull the heads and address the spark plug hole issue. So that's what I'm in the process of doing. I just got the heads off last night and wanted to figure out this spark plug issue by asking for your help and advice. So I appreciate all the help you and others have provided.

The guy at the auto parts store is the one who suggested these NGK plugs and because I knew nothing about the differences in spark plugs, I just went with his suggestions with the impression he knew what he was talking about. Apparently that was a mistake. From what I'm finding out by researching and comparing these two plugs, the NGK UR4 plugs have a heat range of 4 and the 3924's have a heat range of 3. The Autolites also have a 3/4" thread reach compared to the NGK's 7/16" thread reach. So this will put the electrode farther into the cylinder and it will have a hotter spark. I'm hoping this helps with a hard starting issue I've had. We'll see once I get it back together. I have to wait until I receive my ECU back from FAST before I can fire it up and see if there's any difference. In the mean time I'll get the inserts installed and get the heads and intake back on the motor and wait for the ECU to arrive sometime mid to late March.