Setting Gap on Iridium Plugs (2011)

Started on a new thread on Iridium plugs while I sort out my ignition woes.

I have some new ngk BPR7EIX plugs enroute for installation. The NGK website recommends not to change the gap on iridium plugs... I was wondering what others out there were doing, whether they were setting the gap on iridiums to Norton specs or just leaving them as is...

Cheers,

- HJ

What are they set for from the factory? Don't want to go much over .025"

Depends on ignition system and Comp Ratio. Wider gap better until it fails to fire. So can just keep opening up till noticing misfires then close till none at all. Higher CR or weak ignition needs closer gap. Heat range comes into play here as if soot builds up then bigger gap tends to short out rather than jump spark. Timing effects this too. Diddle until thermal stain on hook electrode occurs half way to the bend. Plugs are important heat path for combustion chamber too. Mild soot on bottom rim is considered correct heat range.

I'm running them in all of my British iron, and in all cases I'm following the factory gap setting of 0.031". The thin sharp electrode is designed to allow breakdown at slightly lower voltages (or larger gaps) than conventional plugs. Still, I'm using "high-performance" coils in all of my toys. My Mk3 has a Pazon dual-output coil; its output voltage is not spec'd, so I'm taking Andy's word for it. No problems, though. Instant start, smooth tick-over, and good acceleration. I'm a cruiser kind of guy, so you may want to get opinions from the thrashing side of the forum. Iridiums carry 5 kohms of series resistance, so be sure to use non-resistive caps and wires. Those really attractive NGK caps with the white lettering, BTW, are resistive.

IMO, iridium plugs are the ultimate, I like the Densos over the NGKs because Densos have a smaller diameter center electrode and also the groove on the underside of the ground electrode.

They can explain it better than I can, so here's a link to Nippon Denso's Iridium site -

http://www.globaldenso.com/en/products/ ... tures.html

The thin wire electrode plugs are only an advantage if the thin electrode has a negative polarity. When using a dual output coil one plug center electrode will be at negative polarity and the other will be at positive polarity.

I just stuck them in as they came, I have found they do cause run on now and again. To be perfectly honest I can't tell any difference.

Cash

I put a set of iridium plugs in my race bike. It made 1-2 horsepower more at the higher end of the rev range, but the dyno operator reckoned that it indicates an ignition system that is running at the outer edge of its capabilities.

Jim,

The advantage of sharp conductors lies in the focused discharge path, and thus higher current densities, from one conductor to another. The polarity is simply a convention imposed by us humans. It is irrelevant to the physics of gas discharge. It would be more efficient to have BOTH electrodes sharp, but, alas, mechanics interferes. The advantage of iridium electrode geometry exists regardless of the alternating polarity of a dual-output coil. BTW, I had no idea this was the case with these coils; exactly how does that work?

Rick

Rick,
The lower voltage advantage of a small or sharp electrode happens because the small area tends to concentrate the excess electrons at the point of emission. Electrons are only emitted by the negatively charged electrode so a spark jumping from a large [or rounded] electrode to a small electrode does not get this benefit. [at least that is what they taught me in school].

A dual output coil only has one secondary winding. Each end of that winding has a plug wire attached so when the field collapses one wire will be positive and the other will be negative.

That is why double platinum plugs were created. They have a small platinum electrode attached to the side electrode as well as a platinum center electrode. They are specified for cars using wasted spark ignition and dual output coils. Without two platinum electrodes the plug attached to the positive output of the coil will not get the benefit of the platinum and will erode quickly. Jim

pommie john said:

I put a set of iridium plugs in my race bike. It made 1-2 horsepower more at the higher end of the rev range, but the dyno operator reckoned that it indicates an ignition system that is running at the outer edge of its capabilities.

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I have found installing a new set of plugs is generally worth a horse or two on the dyno. I can't say exactly why but I know it is short lived. Jim

comnoz said:

Rick,
The lower voltage advantage of a small or sharp electrode happens because the small area tends to concentrate the excess electrons at the point of emission. Electrons are only emitted by the negatively charged electrode so a spark jumping from a large [or rounded] electrode to a small electrode does not get this benefit. [at least that is what they taught me in school].

Jim

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Benjamin Franklin earned his bones as a credible scientist in the international community by proving that lightning rods with sharp ends worked better than ones with a sphere at the end. Pretty big deal, back in the day.

rick in seattle said:

Those really attractive NGK caps with the white lettering, BTW, are resistive.

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Not entirely correct. NGK caps as mentioned in black with white lettering, come in both resistive and non-resistive and look identical. There is a very small faint part number stencil on the cap body. check the NGK website. I recently dumped Boyer (non resistive caps) and changed to Pazon who recommend resistive and supply then too.

Mick

ugh, ole Bin [lightening-kite one] and our Bob got the pointy emitter phenomena down, and Tesla the big fat domes to prevent an arc before its time. To nit pick, with dual fire ign. one plug's center electrode sends e-'s off at lower v potential than the other plug broader hook which delays a bit for more EMF to arc e-'s across. A decade ago discussion of this revealed about 15% difference of energy-current, with the pointy negative post polarity on top. So ideally-anally one should set gap ~15% narrower on the reversed polarity plug. This EMF difference-delay to spark also slightly retards timing on the reverse polarity plug, if gaps set same on each plug in wasted spark ignitions. It may also be felt by princess's as a tiny bit of horizontal engine imbalance vibes. Less current/amps flows across the reverse gap than other.

Don't know if filing hook to a point would help or if a different heat range on one side matters in above.
I do know for sure that an over rich tuned Combat I 1st got -before I even knew where the points were- would foul plugs in a few miles until 4 post platinum Bosch plugs tried by day 5 and then a day later went off with locals to drag strip camp out 160 miles away for the avatar tire folding torque testing. Parts of me came apart that day but my Combat never missed a beat.

http://www.nightrider.com/biketech/hdig ... odules.htm

There is a school of thought that states a single fire ignition system produces a smoother running engine than dual fire ignition. Arguments for single fire ignition center around firing the second plug when the cylinder is not on the compression cycle, the 'wasted spark' theory, the 'wear out the plugs' theory, and the 'not enough spark in the right cylinder' theory. Bike Tech is not aware of any hard evidence to support the "smoother running" statements since this is a highly subjective rating. Since many people want to get a smoother running engine, they will perceive that their motor now runs smoother when a single fire ignition system is installed. While it is possible that a specific engine combination does get smoother, it is likely that more than an ignition module setting was changed. Normally the ignition module, coil, spark plugs and plug wires are changed at one time. Any engine that has a few hundred miles on these parts may smooth out when they are changed.

No difference in horse power has been seen between a single and a dual fire engines in testing of 1994 stock 80 CID motors by Bike Tech using the same ignition and coil to test both modes. Bike Tech tested a DYNA 2000 ignition system with a Crane Single Fire coil in both single and dual fire modes. A single fire coil can be converted to dual fire by simply placing a jumper between the two coil positive leads. Testing under conditions where the only difference was the single fire or dual fire mode produced no difference in horse power. Both horse power curves were identical.

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Mick,

When I switched to NGK Iridiums two years ago I searched the NGK website for non-resistive caps that would replace the very cool white-letter 5 kOhm caps I was using. As you can see from the web link

http://www.ngksparkplugs.com/docs/Resistor_Covers.pdf

the white-letter caps are 5 kOhm only. Standard black caps are offered in 1 kOhm or non-resistive flavors. If you have a source for non-resistive white-letter caps, please point me to it, as these caps are much better looking.

Jim,

Does your argument mean that thin-electrode plugs work well in, say, positive-ground machines, but not in negative-ground machines, where the electrode polarity is reversed???

Also, I'm not following your explanation of dual-output coils. Conventional coils are auto-transformers, where one side of the secondary is common with one side of the primary, and from there to the frame; this gives the HT lead a ground reference to the head. Dynatec states that its dual output coil contains two separate secondary windings, each with a common connection to the primary ground, which makes sense. Where is the HT ground reference in your description?

Rick

Rick,
The ground polarity of the machine as far as the battery is concerned has no bearing on the spark polarity, although reversing the primary polarity of the coil will also switch the secondary polarity. If a lucas coil is connected as indicated by the plus and minus symbols then the plug wire output will be negative in reference to the ground (the outside of the case) no matter whether the battery is negative or positive to ground.

The dynatech coil dual spark Harley coil I am familiar with is two separate coils in one housing and is not normally used in a wasted spark configuration although I suppose it could be. It has two separate primary windings and two separate secondary windings both referenced to ground.

Most dual output single primary coils as used on most wasted spark HDs and fitted to British bikes have no ground reference for the secondary winding and only one primary winding. The currant path is out one plug wire ,across the gap, through the cylinder head to the other plug, across the gap and back to the coil. Jim

Hi Jim, so did you said that with a dual output coil (say Accel yellow in my case ) will ask for dual electrodes plugs?

marinatlas said:

Hi Jim, so did you said that with a dual output coil (say Accel yellow in my case ) will ask for dual electrodes plugs?

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That coil would have a single secondary winding so 1 plug wire will be positive and the other will be negative. If you want to run platinum plugs you will need to run "double platinum" plugs to get benefit of platinum on both cylinders. They do not have dual side electrodes but if you look at the bottom of the side electrode you will see a small piece of platinum .

Or you can just run conventional plugs. I would say it is not very likely that a Norton would take advantage of the long wearing electrode in a platinum plug because they are usually replaced due to deposits long before they are worn out.

I would suggest running conventional plugs and replacing them regularly. Double platinum plugs are expensive.

Here is info on a double platinum plug quoted from the Federal Mogal website. Jim

"Champion Double-Platinum Power spark plugs have platinum on both the center and ground electrodes. The center electrode is platinum fine wire that is riveted onto the nickel alloy center electrode. The ground electrode has a platinum pad welded to its surface.

Using platinum on both the center and ground electrodes provides longer life and minimal wear. In addition, Champion’s fine-wire and V-trimmed electrodes create sharper spark focus than conventional plugs. The electrodes on these plugs use our exclusive Heat-Active™ alloy to reach operating temperatures quickly and maintain stable operating temperatures under varying engine loads.

This plug design is widely used for a distributorless ignition with a Waste Spark design. In this kind of ignition system, one bank of spark plugs fires from the center electrode to the ground, and the other bank fires from the ground electrode to the center."


http://www.federalmogul.com/en/Aftermar ... inumPower/

http://www.densoiridium.com/ir_power.php

Good information there.

I see Denso is making an iridium plug with a platinum pad on the side electrode for wasted spark cars. I wonder why they don't use an iridium pad instead of platinum. Jim