FAQ: Which Spark Plugs & Ignition Wires should I use?

GMFreak8 wrote:

How long do the stock plugs usually go for? Are the stock plugs iridium or something else? I'm planning on putting a smaller supercharger pulley on when I get the other pulleys replaced. I could return the iridium and get something else. It's gotta be in stock around here though. What do you recommend? I want to reduce pulley size to the smallest before getting into any PCM mods. I want the best plug for combined longevity and mod friendly performance. No extremes.

Autolite 104s are the most widely used plug for mildly modded 3800s. You prolly wont be able to reduce your pulley size much though without a PCM tune however. Might be able to get away with a 3.6.

L67 wrote:

GMFreak8 wrote:

How long do the stock plugs usually go for? Are the stock plugs iridium or something else? I'm planning on putting a smaller supercharger pulley on when I get the other pulleys replaced. I could return the iridium and get something else. It's gotta be in stock around here though. What do you recommend? I want to reduce pulley size to the smallest before getting into any PCM mods. I want the best plug for combined longevity and mod friendly performance. No extremes.

Autolite 104s are the most widely used plug for mildly modded 3800s. You prolly wont be able to reduce your pulley size much though without a PCM tune however. Might be able to get away with a 3.6.

I'm not really wanting to spend $500 for a PCM tuner, so I'll do whatever I can before requiring it. I figure I'm gonna need pulleys anyway, might as well drop it down a size on the supercharger. I just can't wait for morning to come now. I gotta get this fixed. I'm sitting here going crazy just thinking about it. I feel like I have a kid in the emergency room and I'm waiting to be seen.

GMFreak8 wrote:

Any advice on getting to the rear plugs? They look like a big pain in the ass.

-While I do the same thing myself, the 'look' of the plug wires doesn't mean anything... The cores don't care if we have a nice, clean engine compartment.

-Because Delco had stopped making the OE double-tipped-platinum plugs by the time I got my Riv, I went with the Iridiums and I've had no problems at my level of mods... I do believe that Autolite or Motorcraft does still makes a double-platinum plug, if you prefer.

-My tips on getting at the rear plugs with minimal pain are these: First, release that stupid, in-the-way hood strut from the upper connection point... If it's too cold for the hood to stay up with just the driver's side strut, use a prop-rod of some kind. Second, move the heater hoses out of the way, not by prying them off the metal tubes, but by just removing the set-screws and pulling the metal tubes out of the engine... It's a helluva lot easier that way - just clean & re-lube the openings and the O-rings with fresh coolant before reassembling.

Good luck!

GMFreak8 wrote:

How long do the stock plugs usually go for? Are the stock plugs iridium or something else?

The stock plugs were platinum and probably are good for 100k miles on a well-maintained STOCK car, but maybe 50k-80k for the typical driver (I don't believe most owners maintain their cars correctly). Note the OEM plugs were only intended to support 6-8 lb boost levels, not the higher PSI that comes with modding the engine.

GMFreak8 wrote:

I want to reduce pulley size to the smallest before getting into any PCM mods. I want the best plug for combined longevity and mod friendly performance. No extremes.

Unfortunately there is no "best" plug that can have longevity and performance. It's give & take relationship. You decide: do you want plugs that make YOU more comfortable, lasting 80-100k without concern? Or do you want plugs that make the CAR run more comfortably, accepting the fact they will wear out in 20-30k miles?

Point is, if you want to mod for more power, there can be no fears about getting under the hood for basic stuff like changing plugs. If you prefer not to do it, simply pay a shop $50 every 30k miles (about every 2-3 years). Copper performance plugs are only about $10 for all six. You'll pay close to $50 anyway on the iridium type. If you change your own copper plugs, you'll probably not pay $50 total for the remaining life of the car.

GMFreak8 wrote:

I'm planning on putting a smaller supercharger pulley on when I get the other pulleys replaced. I could return the iridium and get something else. It's gotta be in stock around here though. What do you recommend?

Autolite 104 copper spark plugs, available at AutoZone, or from several online 3800 vendors. Read more about how/why these plugs work starting on page 1 of this thread.

GMFreak8 wrote:

I want to reduce pulley size to the smallest before getting into any PCM mods... I'm not really wanting to spend $500 for a PCM tuner, so I'll do whatever I can before requiring it. I figure I'm gonna need pulleys anyway, might as well drop it down a size on the supercharger.

The smallest SC pulley you can safely go without scanning is 3.6" (assuming 104 plugs, CAI, 180º t-stat). You can try 3.5" and probably be safe, but I recommend a scanner at that point (a real scanner, not a code reader). For a 3.4" pulley, you definitely need to scan, and the price in addition to the mods you'll need will exceed the $500 you don't want to spend on a tuner. So you might as well invest in a tuner right way if you ever expect to run a 3.4" pulley and get the most out of it. There is no going lower than 3.4" without tuning software. See more on basic modding here:

https://rivperformance.editboard.com/series-ii-engine-transmission-f4/faq-modding-101-how-to-increase-acceleration-performance-t23.htm

I've re-read this whole thread, and done some googling, and I still can't find the answer to one question: What is the difference between an Autolite 605 and 104?

Obviously I don't mean the heat range, I mean why isn't it a 604? What other physical attributes are different between the 100 and 600 -series plugs? Doesn't seem right - I've used Autolites all my life, and the rest of the friggin' world should use there simple heat range numbering, but for a given engine I've always used the same series...

Good question. I have no idea.

605 = 1 heat range cooler
104 = 2 heat ranges cooler
103 = 3 heat ranges cooler

Aaron...

Can anyone answer the question that was asked????
Seems a simple enough question, but cannot find it on Autolite's site either.

might help explain it some...

http://www.autolite.com/pdf/SparkPlugNumberingSystem.pdf

As I tried to say earlier i can't find an explanation on Autolite's site that makes sense.

The question asked:

Quote :

I've re-read this whole thread, and done some googling, and I still can't find the answer to one question: What is the difference between an Autolite 605 and 104?

It's all explained in the first post of this thread:

Quote :

The 605 is one range cooler than stock, the 104 is two ranges cooler, and the 103 is three ranges cooler than stock. The 605 plug is good for a stock engine and for drivers with conservative driving habits. The 104 is better for spirited driving, or for moderate engine modification (104s are probably the best plug for most members reading this FAQ). The 103 should only be installed further down the road as you increase boost significantly. Only cars running very high boost and/or used exclusively for racing should use 103 plugs.

The rule for choosing plugs according to INTENSE Racing is:

• Less than 6 lbs of boost: 1 range cooler (Autolite 605s)
• 6-12 lbs of boost: 2 ranges cooler (Autolite 104s)
• 12-18 lbs of boost: 3 ranges cooler (Autolite 103s)

Autolite spark plugs are broken down into families which are designated by thread size, reach, hex size or tip design


I'd guess there is some relatively inconsequential difference between the 6 series and the 1 series that prompted them to assign a different first digit. Maybe one or the other is ever so slightly longer, etc. I also can find no specific explanation.

Aaron, that's not what's being asked. What is the difference between the 6 series plugs and the 1 series plugs???

I think I have the answer. Looking at the online specs for the 103, 104, 605, and 606, the only difference I see noted, besides the heat range, is that the 6 series plugs are described as "Copper Core Large Gap", while the 1 series plugs leave out the "large gap" notation from their description.

Yeah Dave, I found that one explanation, too... but they don't list which numbers mean what. That next post of yours sounds like a possible, but aren't they both 60-thousandths?


Aaron, if you read the 2nd line, you'll see that the question asked was:

Quote :

Obviously I don't mean the heat range, I mean why isn't it a 604? What other physical attributes are different between the 100 and 600 -series plugs?

Part Number 606
Product Type Resistor
Description Copper Core, Large Gap
Heat Range Chart Location D14
Hex 5/8"
Reach .708"
Resistor/Non-Resistor/Suppressor Suppressor
Seat Tapered
Thread Diameter 14MM
Tip Power

Part Number 605
Product Type Resistor
Description Copper Core, Large Gap
Heat Range Chart Location D14
Hex 5/8"
Reach .708"
Resistor/Non-Resistor/Suppressor Suppressor
Seat Tapered
Thread Diameter 14MM
Tip Power

Part Number 104
Product Type Resistor
Description Copper Core
Heat Range Chart Location D14
Hex 5/8"
Reach .708"
Resistor/Non-Resistor/Suppressor Suppressor
Seat Tapered
Thread Diameter 14MM
Tip Power

Part Number 103
Product Type Resistor
Description Copper Core
Heat Range Chart Location D14
Hex 5/8"
Reach .708"
Resistor/Non-Resistor/Suppressor Suppressor
Seat Tapered
Thread Diameter 14MM
Tip Power

The 104's I bought were gapped from the factory at .065, It was uncomfortable to reduce the gap to .050, which is where i wanted them gapped to.
The ground electrode required a lot of manipulation to get it perpendicular to the center electrode and gapped properly.

Thanks for that research, Dave. Even if that nomenclature doesn't make sense if they're both pre-gapped to +/- .060,
we now know that the seat and the reach (what I was really wondering about) are the same.

Rickw wrote:

The 104's I bought were gapped from the factory at .065, It was uncomfortable to reduce the gap to .050, which is where i wanted them gapped to.
The ground electrode required a lot of manipulation to get it perpendicular to the center electrode and gapped properly.

That's funny, the 104's are the ones that don't say 'large gap'...
Have you played with 605's as well, Rick?

Ok, you're asking why Autolite chose the numbers they did. I didn't understand you.

3rd number is the heat range: 6 is stock (0), 5 is (-1), 4 is (-2), 3 is (-3)

2nd number references resistor/non-resistor/suppressor spec: even #s are resistor, odd #s are non-resistor, and I assume zero means suppressor type.

1st number, according to Autolite "designates a sub-division within a plug family", indicating a special seat taper, or reach.

There can also be a 4th (new first) number to designate further sub-divisions.

So all AL plugs have at least two numbers. If plugs within the same family have differences, they add a third number to create a group. If plugs within that group have differences, they add a fourth.

Eldo wrote:

That's funny, the 104's are the ones that don't say 'large gap'...
Have you played with 605's as well, Rick?

No, not yet, but i plan to when the weather gets warmer I'd like to try a set of 605"s and run them for a while while scanning and also be able to pull them and read them. For now I'm leaving the ones i have in there as everything is tuned with these plugs.
I did pull one within the last two weeks to read it visually, could not find my magnifier, and it looked good. If anything it looked too good. Looked lean to my eyes, but went on a tuning run with Derek and all was good.
I'm still looking forward to doing some more experimentation with plugs, unless i put the Gen V on sooner than i think, then I will stick with the 104"s.
IDK, if i get my own Tuner software, I might still have the desire to experiment with heat ranges. Where not talking about big differences here between 605 and 104's from what I'm told. But I'm still curios.

NAPA didn't have the AC Delcos so I got these - what do you think?

invisible plugs? i like that!

They'll work. I think 605s or 104s would be better for summer.

I don't have any mods, the 104's have started caking up.

NAPA didn't have 605's. I asked cause I hadn't heard of anyone running 606's.

BTW how should I gap these 606's?

.058" should work fine. Use a gap tool or feeler gauge to set.