Hi All, Whats is the deal with iridium plugs? Twice now my bike has been to the workshop and the mechs have thrown away my iridium plugs explaining they are shite and should not be used! When fitted I can feel no difference in power, no difference in torque, if anything the bike starts nicer than with regular plugs... So why do tuners hate them when they work perfectly well and last almost forever? Cheers.
If you take the air fuel mixture and compress it as your engine does, a match will make it go bang just as well as a spark plug. The spark energy comes from the electricity and when that jumps a gap it sparks, there is not a better spark or a spark that explodes the mixture better.
It's because they don't perform as well as copper plugs, you could probably measure the difference on a dyno. The counter argument to this is because they don't erode as fast as copper they perform better over a length of time.
If you consider that the energy (power) is in the amount of air/fuel mixture in the cylinder, then the spark that is used to ignite that mixture cannot really influence the energy released. As I said before a match would release that energy, so would a different type of match be able to release more energy? I doubt it because the energy (power) is not in the spark. Someone will be along soon to say that they got more horsepower with a certain make of plug, but that would not be possible without more fuel.
And more oxygen. That's what I thought, from a scientific point of view the above makes perfect sense. Could a larger spark ignite more fuel/air mixture than a tiny spark? In theory I guess yes, but is this even measurable?
Not really because the spark, whatever size, just starts a chain reaction which will burn the air fuel mixture, as long as ignition occurs that the size of the spark should make no difference.
If you were to upscale the experiment I think you would see an decrease in ignition time for a given mass of air/fuel. Fill a stadium with a/f and ignite with a tiny spark in the a far corner compared to a spark the same size as the stadium. The larger spark would set the chain reaction from many more molecules than the tiny spark but in a combustion chamber, in a small cylinder head, with sparks of almost equal size, no, I don't reckon the difference is measurable. Any tuners here care to share their knowledge?
The speed of the burn (chain reaction from the spark) is determined by the octane rating of the fuel and the efficiency of the movement of the burn is in the combustion chamber design. I don't think that it could be measured either.
As per the title below, Larry Kelly's view also known as Shazaam on other Ducati sites, you pays your money. I use Magnecore wires on my 748R which runs surface discharge plugs and they give a much improved spark as these plugs need it as they foul easily on start up. Platinum and Iridium Spark plugs by Larry Kelly Regarding the use of platinum and iridium spark plugs in a Ducati, platinum or iridium plugs will give you worse performance than a conventional plug unless you use a larger gap than is recommended for the steel electrode plug equivalent. One by-product (and benefit) to having platinum or iridium as an electrode material is that the harder material erodes more slowly and consequently allows you to reduce the size of the center electrode and still have a long-lifetime plug. Re-gapping is infrequent or eliminated. In fact, the initial reason this type of plug was developed was an attempt to meet the 100,000-mile durability/maintenance requirement mandated by the US EPA for exhaust emissions, not because they offered any improved performance over conventional electrodes. A smaller electrode, however, will arc at a lower voltage. This is good because the lower arc-over voltage is not as demanding on your less-than-new ignition coils and wires so the firing is more reliable. But this is also bad because a lower arc-over voltage presents a weaker spark kernel (lower arc current and duration) that is less likely to light off the air/fuel mixture. Consequently, dyno testing shows a performance gain with specialty plugs only when their intrinsically lower arc-over voltage has allowed users to increase the plug gap above that possible with conventional steel electrode plugs. A larger plug gap needs a higher arc-over voltage to fire, and a larger gap, combined with good plug wires and coils, will span more fuel molecules resulting in a more reliable burn with fewer misfires. So you get better throttle response. Not more power, just better throttle response. Conversely, I have seen several examples of Ducati throttle response problems cured by replacing platinum/iridium plugs that were gapped too small i.e. the 0.024 inches / 0.60 mm Ducati recommends for conventional plugs. Both NGK and Denso pre-gap their Ducati application specialty plugs to 0.035 inches / 0.9 mm. This should be considered a minimum gap for this kind of plug. If you have a older bike, you may arc-over the plug wires before you can fire an optimized larger plug gap. If the spark plug wires have inadequate insulation, the wire cannot maintain a high enough voltage across the insulation and will arc to ground before firing the plug gap. The factory spark plug leads are stranded wire covered with an EPDM jacket and although the wire itself will last a long time, the insulating jacket will start to break down after a couple of years which is why most good aftermarket wire is insulated with silicone. If this becomes a problem, replace the stock spark plug wires with a set of Magnecore or similar quality wires. This will allow running a larger plug gap without a concern for insulating the higher voltage needed to jump the gap. For road bikes you should use carbon core wires, preferably carbon wires with a spiral wrap center conductor. Straight, multi-stranded, unshielded wire conductors offer theoretical gains resistance-wise, but produce lots of electromagnetic interference (EMI). One major concern is with the computer found used on fuel injected bikes since the radiated EMI can interfere with the computer and corrupt sensor and internal signals which can affect engine performance and reliability. This concern also extends to the use of non-resistor type spark plugs.
The trouble with things that you read on the internet is that they could be written by anyone who might be knowledgeable or might not be. The above statement might make you believe it or you might ask to see the figures. This part says no more power, that is obvious as the power is produced by the energy in the fuel, but as a dyno measures power how is he seeing the performance gain that he talks about in the first paragraph?
This guy sets himself up as a Ducati guru but I know for a fact that what he says about how the quiet clutch mod works is totally wrong, so my faith in his statements could be more absolute than it is. However, Since I installed Iridium plugs, with the pre-set larger gap, my 999's idle has been steadier and pick up has been more precise. I did install a cable kit at the same time though and others have suggested that that makes a difference to their idle and pick-up, so I don't know which it is that's made the difference. So, the performance may not be any better but it's no worse either and the plugs are pretty much fit and forget - what's not to like??
I would expect that, with a larger gap the tickover might be more precise, but to be fair did you also try brand new "normal" plugs at the same time? Comparing a new Iridium plug to a well used "normal" plug is not very scientific. At tickover the used "normal" plug might miss the occasional spark making the engine feel a bit rough, but if there is a spark there, even a weaker one, then I would expect it to ignite the explosive mixture in the cylinder.
Some manufacturers, including Ducati, have gone to considerable expense to fit twin-plug heads to some models. They seem to think there are advantages to having two sparks in the combustion chamber instead of one. Do you think they are deluding themselves?
No not at all. The air fuel mixture is explosive but even an explosion does not happen everywhere instantly. Different octane fuels burn faster or slower so the maximum burn expansion happens when the piston is well past TDC that is why ignition timing is so critical in a modern engine. By fitting two plugs the burn can be started in two different places in the combustion chamber which, in effect, makes the burn seem like it is faster without having to use higher octane fuel. It allows the engine manufacturer to be very precise in their settings and get the most energy out. My wife and I had a pair of BMW R1100S's, great bikes, but mine was a twin spark and hers was a single spark. They were both exactly the same in power output and the feel of the bike in every way. We went out together all of the time and rode exactly the same routes at the same speed. When we filled up my twin spark used to do 46 mpg and her single spark 44 mpg.
Great responses. Pros and cons for both it seems. I was just interested to find out why tuners don't like them.
Nope. I can only speak from experience....When I tried the iridium plugs the bike(s) ran very poorly....Others may have a different view. My MTS TS engined track bike is running on one plug per pot. As Sev (and believe Nelly in the past) has said the TS is really about cleaner burn/emissions/maybe a bit better running at low revs....Maybe.
