Spark plugs?
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Road Master
Joined: Dec 2014
Posts: 994
Likes: 43
From: Essex, England
Spark plugs?
Have spark plugs actually evolved? There was the traditional, then the iridium tips, then the multifire/electrode Brisk types and now the E3 things. I normally just order whatever is spec'ed in the owners manual but am I just being a Luddite? Anyone ever seen any benefits on a dyno from different types of spark plug? Or anecdotal wise noticed any starting/running difference?
Club Member
Joined: Feb 2007
Posts: 16,320
Likes: 306
From: Boynton Beach, FloriDuh
+1 - Iridium plugs are the only ones I would label advanced in that they are typically good for ~100,000 miles. They're ideal for use in many modern vehicles where changing the plugs in some cases is extremely difficult because the plugs aren't accessible.
Plug accessibility is hardly a problem on a Sporty.
Plug accessibility is hardly a problem on a Sporty.
Road Master
Joined: Dec 2014
Posts: 1,036
Likes: 45
From: Florida
I like to use NGK Iridiums and never had any problems with them. I have noticed better starts with older carbed Sporties. Many will be against them because they don't have the Harley Logo on them and they are not spec, but in turn they will use other manufacturers oils. I have yet to see any valid argument that the stock plugs are better than the iridiums other than "claims" that the iridiums affects the knock sensor. I have not noticed that problem. I attached a video of a dyno run on a touring Harley showing stock vs iridium plugs results.
Road Warrior
Joined: Nov 2013
Posts: 1,843
Likes: 1,976
From: Eastern,North Carolina
I do agree with that, I use to have a Honda 600cc 1cyl thumper that you had to kickstart. I rode it to work on pretty cold days and it would fire on 1 or 2 kicks with these plugs while standard plugs would take several kicks.
Club Member
Joined: Feb 2007
Posts: 16,320
Likes: 306
From: Boynton Beach, FloriDuh
I like to use NGK Iridiums and never had any problems with them. I have noticed better starts with older carbed Sporties. Many will be against them because they don't have the Harley Logo on them and they are not spec, but in turn they will use other manufacturers oils. I have yet to see any valid argument that the stock plugs are better than the iridiums other than "claims" that the iridiums affects the knock sensor. I have not noticed that problem. I attached a video of a dyno run on a touring Harley showing stock vs iridium plugs results.
Road Master
Joined: Dec 2014
Posts: 1,036
Likes: 45
From: Florida
Yeah I should have been more specific with that since I deal within a broader range of Harleys including the VRODS and not just specifically with the Sportsters. My bad but you get the point I was trying to share. I hope the example dyno run that shows a Harley touring bike don't confuse people also.
Last edited by Cool Inferno; Sep 3, 2015 at 02:51 PM.
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Extreme HDF Member
Joined: Dec 2007
Posts: 13,402
Likes: 941
From: Illinois
Iridium plugs are self cleaning and will last 100K miles. But the main reason that they are in most new cars is that they ignite E10 87 octane gas better than other plugs. Since that is all that I use in everything from the 883 to the 110 CVO's I use iridium NKG plugs. More mpg's.
My 12 RGC gets 52 mpg, the 12 RGC 110 CVO gets 50 mpg and my 03 883 gets 57 mpg. I gave up on high octane gas for HD low compression mild tuned engines long ago.
Who cares about mpg? Me! I ride over 30,000 miles per year. I save $0.60 per gallon over 91/93 in this area on over 600 gallons of gas that is at least $360 dollars. A side benefit is that a little more power is produced with the more complete burn in each power stroke.
Gas stations for several weeks before Sturgis when I rode through on a return trip from Canada had raised high octane prices to $1 dollar over regular. They were ready for the HD crowd!
If you install cams and raise the compression then 91 or better is needed and regular copper core plugs do the best job.
My 12 RGC gets 52 mpg, the 12 RGC 110 CVO gets 50 mpg and my 03 883 gets 57 mpg. I gave up on high octane gas for HD low compression mild tuned engines long ago.
Who cares about mpg? Me! I ride over 30,000 miles per year. I save $0.60 per gallon over 91/93 in this area on over 600 gallons of gas that is at least $360 dollars. A side benefit is that a little more power is produced with the more complete burn in each power stroke.
Gas stations for several weeks before Sturgis when I rode through on a return trip from Canada had raised high octane prices to $1 dollar over regular. They were ready for the HD crowd!
If you install cams and raise the compression then 91 or better is needed and regular copper core plugs do the best job.
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Stellar HDF Member
Joined: May 2007
Posts: 3,256
Likes: 522
From: USA
I have no cite for this statement.
Copper core (center electrode) plugs carry electricity better (stronger) than Iridium, Platinum etc metal plugs.
The exotic metals wear longer than copper hence their benefit.
For years there have been multi ground electrode plugs and yes these can provide a hotter spark. But rarely is there a horsepower increase.
Best, for maximum performance, with any single ground electrode plug is indexing the plug.
Copper plug replace every 10K and indexing on a Harley...yes I think that is fun maintenance.
Copper core (center electrode) plugs carry electricity better (stronger) than Iridium, Platinum etc metal plugs.
The exotic metals wear longer than copper hence their benefit.
For years there have been multi ground electrode plugs and yes these can provide a hotter spark. But rarely is there a horsepower increase.
Best, for maximum performance, with any single ground electrode plug is indexing the plug.
Copper plug replace every 10K and indexing on a Harley...yes I think that is fun maintenance.
Tourer
Joined: Sep 2013
Posts: 259
Likes: 0
From: NJ
I started using NGK Iridiums back when I was playing with two stroke dirt bikes, and then racing 125 GP bikes, because they'd foul less often on me. My last Grand Caravan went 110,000 miles on a set of iridiums installed at the factory. When it's time to swap plugs, I'll put a set in, then check them at the change interval to see how they've worn compared to the O.E. plugs.