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Best spark plugs?

what are the best spark plugs to run in an early 3.0L? i notice pelican has lots of options

Old 11-06-2014, 11:29 PM
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Hard to say which ones are best. Currently I'm using NGK BKR8EIX iridium plugs and they work fine. They were around 7 bucks each somewhere on ebay with free shipping. Do a search you'll find someone selling them. Autozone has them too.

In the past I've used Bosch W4CS silver and Bosch W3DPO platinum were in my car when I got it and they all worked fine. I guess you'd have to find someone with more experience that's done dyno runs on the same day with each type of spark plug.

Some people have supposedly had fouling with the cold W3DPO plugs when driving around town all the time but I never did. They may have been running too rich or burning some oil. I still have them stashed in a drawer.

Don't sand blast spark plugs to clean them because sand particals can get wedged up in between the white insulator and steel housing around it. If you see it in there you may not be able to reach in there with a sewing needle or something and dig it out.
Then when running them in the car the sand would probably come out when they heat up and then scratch a cylinder wall and piston.
Old 11-07-2014, 09:15 AM
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I am also running the NGK iridium plugs. I would guess it also has to do with if you are running stock or not.
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Old 11-07-2014, 09:22 AM
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I used both the NGK and Denso iridium with good results.
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Old 11-07-2014, 11:30 AM
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Here is my tech note on spark plugs, and a comparison chart on some popular plugs (items in red were show-stoppers for me).



Do you have a stock setup with capacitive ignition? The W3DPO's are still a pretty good choice.

When I looked at the choices for myself, I considered these factors:

Ignition system type (capacitive or inductive)
High tension wire type (spiral wound or solid core with shield and resistor)
Combustion type (single plug or dual)
Longevity desired
Heat range

Ignition System
If you have the original or an aftermarket capacitive ignition system, the voltage rises very, very fast. In fact, it happens too fast, so most capacitive systems discharge several times for each cylinder firing to emulate a longer spark. Capacitive ignitions do not like resistance because it reduces the spark energy (voltage over time) at the gap. For stock 930's the total resistance from distributor end to spark plug is 4K.

Inductive ignitions, whether wasted spark or COP produce a long duration spark. Since they only strike once, resistance is less critical. If wires are used, they have a spiral construction to reduce EMI, and use a resistor plug for RF suppression. Typical wire resistance is 5.5K/meter. A resistor type spark plug is typically 5K. Thus, the total resistance from distributor end to spark plug is around 8K.

Wire Type
If you want to stick with the Beru metal shielded cables, then you shouldn't use a resistor plug, as the Beru metal shielded cables have the 3.5K resistor build into the connector. It can be removed, if you want to take that route. Then you could/should use resistor plugs.

Most, if not all of the aftermarket spark plug wires are spiral wound steel wire with a silicon cover, with about 5K per meter resistance. On a capacitive system it would be better not to use these wires and a resistor plug, as the combination of resistor plug and spiral wires have too much resistance.

Combustion Type
The big combustion chamber of the 930, and the giant valve sizes, make it hard to get the spark plug close to the center. For this reason, Porsche specified a longer protrusion in the stock spark plugs electrode to get it further in. This really is only a part throttle and idle thing. Not so big of a factor at WOT.

If you twin plug (not something I recommend), you can do away with this and use a standard protrusion, which protects the center electrode a little better.

Longevity
In fact, all spark plugs are copper plugs! The fancy metal is too expensive to make the whole thing out of it. The core is copper, but the tip is something else. Copper erodes over time, increasing the gap. Also, newer plugs have fine wire center electrodes. Why? So that it will heat up faster and burn off the combustion products. This usually makes for a better idle. If you are not too fussy about idle and want to change plugs a lot, copper is fine.

Heat Range
There are lots of cross references on line to convert from a Bosch heat range to that for other brands.

Old 11-07-2014, 04:57 PM
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^^Thank you guys for all the very informative and educational replys. I think i made my decision

Old 11-09-2014, 02:00 PM
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