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

The type of plug you use will depend on your level of modification. A good upgrade for a stock engine is to replace the OEM plugs with a type known as "cooler" than stock. A good copper spark plug is the Autolite 605 or 104. Autolites are very reasonable at about $10 for a set of 6, and can be found at most auto parts counters.

The idea behind cooler plugs is that they will dissipate heat away from the electrodes more quickly than standard plugs. Since excess heat in the combustion chamber is one of the chief causes of knock in the L67, running cooler plugs helps to lower the chances of it occurring.

Understand that a cooler plug does not have a "cooler spark". The reason a cooler plug stays cool is because it has a smaller insulator, so heat can more easily escape. 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)

The size of your SC pulley and the mods to your engine/exhaust will determine your level of boost and the plugs you should use. Using plugs that are too cool can result in plug fouling. This is a condition where a plug's electrodes become coated in soot/debris, preventing easy starting or even causing misfires. We have so far found zero instances of plug fouling, even using 104s with a completely stock engine. Since our engines make 6-8 PSI in stock form, either 605s or 104s will work. Lean toward the 104s if you plan to be in the throttle a lot.

A note about platinum/iridium plugs: some people use them with success, but they generally aren't considered the best performance plug for our supercharged engines, especially if you'll be doing any racing or frequent WOT activity. It's generally thought that copper plugs are the best performance plug for our engines because copper runs cooler and happens to be a lot less expensive. The chief advantage with platinum and iridium plugs is they will last a long time - perhaps 100k miles versus 50k miles for a set of copper plugs. But if performance is your primary goal, it makes sense to change out the plugs once every 1-2 years anyway, being that they are inexpensive and easy to replace. So, even if you only get 20-30k miles out of a set of copper plugs, it's nice to know that you always have a set of clean, fresh plugs making good spark. And although some say platinum/iridium plugs offer better fuel economy, it's probably a very slight improvement, if any, over a fresh copper plug. In fact, since copper plugs get replaced more frequently, there's a chance you'll see better efficiency with them because the electrodes will be cleaner and any damage will not go overlooked.

Although tempting, it is probably not worthwhile to upgrade to aftermarket plug wires. The OEM (AC/Delco/Delphi) wires have proven to be worthy performers. You should replace your wires at least by 100k miles, or a bit earlier if feasible. A new set through the dealership is $59.99, but they can be found for as little as $35 if you shop around.

kinda weird, but the first time i modded the riv, i ran a wai, dp, full exhaust, 3.25, and 1.5 range colder plugs (R42LTS). the second time, i ran a fwi, dp, full exhaust, 3.4, and powrtuned and a .5 range colder copper plug caused my car to run poorly, so i ran a .5 range hotter ngk iridium plug and it fixed the problem i was having.

Looks like lots of variables in your set-up that made your situation unique. In my experience, 1/2 range changes don't make that big of a difference. If you go cooler, your engine should run the same, but the chance of fouling increases.

The fact that you changed plugs period may have fixed your problem. Also, gap and plug material could make a difference, although copper has given the best results for most.

the stock range platinum plugs i replaced w/ the coppers caused it to act the same way. i was totally perplexed (sp.?). the exhaust would kinda pop like it was backfiring. i did run a smaller gap though. idk, it was weird. i, too, like to use copper plugs instead of Ir/Pt. a local clubgp memeber suggested i try those plugs and they worked, so i was happy.

I did not know of any concerns with using lower heat range plugs. I put in 2 range colder 104s in mine because I knew eventually I would anyway.

What are the downsides to using cooler plugs?

Plug fouling is the only real concern. Over time the electrodes may blacken and cause a hard start or misfire.

its better to use a tuner to get rid of kr instead of trying to mask the problem w/ colder plugs. its best to run a hotter plug (in releation) cause they burn fuel better.

I remember in the original FAQ for the Riv it said it is good that the plugs require frequent changes. Guess that is a positive to some!

To me it is, I just have to remember all of my replacement schedules...

i went to the partstore tonight and went to get some auto lite 104. they told me they are the same thing as the 605's are they full of it or what? what ones shouls i get for my car and do i have to gap them or are they pre-gaped.

I think they are pre gapped, not sure tho. They are different hence the different number. They are one heat range cooler than 605s and two ranges cooler than stock.

quote from top of thread:

• 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)

104s and 605s are not the same, but both can work in your application. A lot depends on your driving style. If you're not aggressive, 605s are better. If you're hitting WOT a lot, 104s will work fine. The only danger of going too cool is fouling of the electrodes.

As mentioned, gap to .058". Plugs are pre-gapped, but they are not the correct value, and if a box gets dropped or shifted during shipment... never trust a pre-gapped plug.

Basically my only plans in terms of modification right now is a 3.4 pulley & intake plumbing (and 180 tstat & higher flow mufflers in case it makes a real difference) and i will pretty much always be using 91-93 oct gas just depending on what station i go to. my question is do i want to use 605 or 104 plugs?

with the 3.4 you will need 104 plugs. you could run the 605's until you get the 3.4" pulley on.
IF you pull the 104's out and they look burnt then you may want to go to 103's.
the only draw back to running too cold of a plug would be fouling the plug. and i've never foulded them. go WOT every once in awhile to keep them clean and your good. also the autolites are the best and also the cheapest so if they do happen to go bad or foul then a new set is only like $7

thanks much. im assuming 103 is the next colder after 104. just out of curiosity, what kinda plugs do people use who are running like 3inch pulleys and stuff

yes 103 is 3 ranges colder than stock. 103 is about the coldest people go b/c if your running a 3" or 2.9" pulley then you have tuning done and a range colder plug will not do much to prevent detonation. colder plugs are only part of what we do to prevent KR

my friend was able to "acquire" a set of autolite 104 platinums. would those be fine to use instead of the coppers?? i HOPE so...

I think the platinums are hotter. I'm not the expert, but that's what I'm led to believe. I could be wrong though. Can you exchange them SOMEWHERE and AQUIRE the copper?

jax95riv wrote:

I think the platinums are hotter. I'm not the expert, but that's what I'm led to believe. I could be wrong though. Can you exchange them SOMEWHERE and AQUIRE the copper?

i was hoping they would be the same as copper 104s, just platinum which under normal retail circumstances would be an unnecessary feature

They'll work ok, especially if you aren't racing all the time. In theory, the platinums do run hotter because the spark is focused at a specific point, whereas the copper distributes the spark around the electrode because it is a cylindrical shape.

For everyday driving, you won't notice a difference, and the platinums will last twice as long (their only real advantage). But when you are going WOT, and you want as little KR as possible, I always prefer coppers. And as I've said before, who really wants to keep a set of plugs in for 50k miles anyway?

those plugs would be colder than stock still right. Right now I have the stock NGK iridiums in there and since i'm hopefully putting on the pulley this weekend, i'd like to have the thermostat and plugs ready also

Yes, they'll be an improvement because their heat range is lower. This means they let more heat escape the combustion chamber. You're not going to notice anything, but when you get that 3.5" SC pulley on, it'll keep the knock down.

wish i had a good scanner

all the actron tells you is net advance. can you figure out what KR with that or no

No, but if your timing is pulled much below 12 at WOT, there's a good chance the PCM is correcting for excessive knock.

codith, you and me have it hard trying to determin how the engine is running w/o a KR indicator. my autera scanner shows everything but.
you can baisicly tell how safe it is running by looking at O2 readings at WOT, timing advance (may be like mine and show negative when it really means positive), LTFT, and by keeping track of the fuel you put in, temps etc.
you cant have less than 0 knock so do all the supoting mods you can to make sure its running right.

Has anyone used NGK plugs on a 96 Rev 3800 SC ?
If so, what part #?

I cant find Autolite's here in Ontario