Iridium vs. Platinum spark plugs for stock engines

[lonewolf]

Does iridium make any real performance difference over platinum plugs in stock engines?

Do they really last 6+ times longer than platinum?

Is there any difference in quality between iridium brands like Denso, NGK, etc.?

[onegunguitar]

I take it the plugs you are talking about are for your bike. I always run NGK's in my Kawasaki and my Yamaha,I never really used the other brands but my buddy has a bike and atv shop and I'd bet he'd recommend NGK's. I've seen SplitFire plugs work great and other times no difference,except in price If I were you I'd just run whatever the oem calls for in a stock motor.

[lonewolf]

I take it the plugs you are talking about are for your bike. I always run NGK's in my Kawasaki and my Yamaha,I never really used the other brands but my buddy has a bike and atv shop and I'd bet he'd recommend NGK's. I've seen SplitFire plugs work great and other times no difference,except in price If I were you I'd just run whatever the oem calls for in a stock motor.

I use NGK's for my bike too, but this is for a BMW Z3 2.5L "Technical Upgrade" engine. Each plug has its own coil assembly mounted above the plug.

[onegunguitar]

I take it the plugs you are talking about are for your bike. I always run NGK's in my Kawasaki and my Yamaha,I never really used the other brands but my buddy has a bike and atv shop and I'd bet he'd recommend NGK's. I've seen SplitFire plugs work great and other times no difference,except in price If I were you I'd just run whatever the oem calls for in a stock motor.

I use NGK's for my bike too, but this is for a BMW Z3 2.5L "Technical Upgrade" engine. Each plug has its own coil assembly mounted above the plug.

Oh,haha,good luck then Jeff!

[JackANSI]

Iridium is an extremely dense metal (might be the most dense on the table I think). It conducts heat and electricity fairly well. It allows for a thinner electrode that keeps its gap better which allows for a more predictable spark in a wider range of conditions (inside the combustion chamber).

Similarly platinum doesn't react easily with the chemical process involved in combustion, so it doesn't suffer from chemical degradation as quickly as other types of plugs. This allows the same predictability, thinner electrode, and consistant gap as iridium.

There isn't much difference I've found in iridium vs platinum except when using race fuels. But I would go with platinum if you're going to feed your vehicle with <=89 octane gas. It'll be more resistant to the garbage in the lower grade gas.

What I've learned:

The longest I'd ever recommend using a plug, even if its still in great shape and made out of the fingernails of jesus, is 75K miles or 3 years.

I've never had a problem with NGK plugs, I trust them.

You'll never feel a difference in performance between two sets of new plugs, even back to back. All of the performance gain you feel with new plugs is because what is going on in the combustion chamber is more in-line to what the ECU/physics is predicting will happen.

If its going to see daily driving duty (60% highway, 40% city) and you're not burning any oil:

Normal copper plugs should be replaced every 10K-15K miles no matter what gas you use, gap checked and electrode read when you change your oil.

Platinum:
If you use crappy gas (87-89 octane) you won't get any benefit from longer lasting plugs except an increase to 30-40K miles between plug changes and about 10K between reading and gap checks. Your plugs will be ready for a change after about 40K.

If you use better gas (91+ octane) you will be able to go 15K-25K between reading and gap checks and the plugs should last a good 60K easy.

In forced induction engines, I've never had a good result with those E3 plugs. You end up with more hot spots (these cause the worst kind of knock) under consistantly heavy loads like a track day or climbing a long uphill grade. They work just as good as any other plug on NA engines. They are also a copper electrode so you need to change them as often as any other normal plug.

Learning to read your plugs and checking them often can really be an eye opener to the condition of your engine and its sub parts. In one summer you can get a feel for how fast your plugs wear and you'll pick up a rhythm for your car maintainance if you read and gap your plugs every few weeks. You can also guage if you need colder or warmer plugs to help extend their working life.

Also if the plug is 'double plated' as in the electrode is tipped with iridium or platinum and the ground electrode (the arm sticking off the casing) has a plating (usually a small square raise section) they usually come pre-gapped and you should NOT regap them. You could allow the spark to reach the non-plated portion of the ground electrode, which it wasn't designed to handle. I know NGK uses a -# after their model number to denote what they are pregapped to. Like BKR7ES-11 is a BKR7ES with a 1.1mm gap.

[lonewolf]

Iridium is an extremely dense metal (might be the most dense on the table I think). It conducts heat and electricity fairly well. It allows for a thinner electrode that keeps its gap better which allows for a more predictable spark in a wider range of conditions (inside the combustion chamber).

Similarly platinum doesn't react easily with the chemical process involved in combustion, so it doesn't suffer from chemical degradation as quickly as other types of plugs. This allows the same predictability, thinner electrode, and consistant gap as iridium.

From what I've read about iridium plugs, the significant difference is that the electrode's arc surface can be significantly (like 40%) smaller than the other materials, including platinum. The smaller arcing surface requires a lower voltage to produce spark--up to 5,000 volts less. This might be a good thing for wear on the coils, especially if you have 6 of them, each mounted directly on each plug and bolted down with two bolts. Changing, cleaning or gapping plugs ain't no picnic with BMW like on most other cars. You have to remove an engine cover, 12 bolts, 6 coil assemblies & two ground straps just to get to the plugs.

There isn't much difference I've found in iridium vs platinum except when using race fuels. But I would go with platinum if you're going to feed your vehicle with <=89 octane gas. It'll be more resistant to the garbage in the lower grade gas.

My engine requires 91 and it usually gets 93, if not, 92. I kinda thought that with standard fuels, there wouldn't be a noticable difference in performance between the two. The iridium might have a more consistent spark, but you probably wouldn't notice it driving down the road. It might result in a minimal gain in MPG.

[Ron]

I would highly doubt if the lower spark voltage would have any change on the ignition coil life. The secondary side of the ignition coil is basically passive and doesn't see any significant current. The only thing I can see going wrong on the secondary side is breakdown of the insulation over time.
The primary side and the switching components take all of the abuse. 12V directly across the terminals, back EMF, etc.

[JackANSI]

NGK platinum and iridium tips are the exact same diameter.

Coil-on-plug hardly wear out unless you let plugs go well beyond their recommended gap.

On a stock WRX to get to the plugs, you need to remove the wiper reservoir, battery, and intake filter box just to get to the plugs. Its coil-on-plug too, except you are working horizontally with frame rails and wheel arches in the way.

Your BMW is a cake walk to change plugs.

Feel free to duplicate my experience with plugs if you want.

[lonewolf]

NGK platinum and iridium tips are the exact same diameter.

Coil-on-plug hardly wear out unless you let plugs go well beyond their recommended gap.

On a stock WRX to get to the plugs, you need to remove the wiper reservoir, battery, and intake filter box just to get to the plugs. Its coil-on-plug too, except you are working horizontally with frame rails and wheel arches in the way.

Your BMW is a cake walk to change plugs.

Feel free to duplicate my experience with plugs if you want.

Nah, hot babes don't wave and get whiplash when a Subaru goes by.

[JackANSI]

Let's take it to the track


If you ever need a hand doing something to the car let me know.

[lonewolf]

Thanx.