Platinums are worth the extra bucks, IMO....When my bike was new, it developed a miss suddenly at about 6500 miles with the regular HD plugs. I replaced with the same and had the same results. I replaced those with HD platinums. I ran those 30k miles before taking them out. They were still running fine. I only took them out because I had put in new cams and a DFO and wanted to monitor new plugs. My last set of platinums have 24k on them and are still going strong.

Which ever plug you choose, stick one of the old ones in your tool bag. A bad plug on the road is no fun in a V-Twin engine.

 

This topic just came up in the Sportster section.
https://www.hdforums.com/forum/sport...ark-plugs.html

Here are my responses:

...I upgraded to Denso Iridium fine-wire plugs in my '09 1200 Custom. Essentially it goes back to the days when I owned an airplane. There are basically 2 types of spark plugs: massive electrodes and fine-wires. On a 6-cylinder aircraft, there are 2 plugs per cylinder for redundancy purposes. Regular massive electrode plugs run $25 each but would require more frequent maintenance (greater chance of potential damage by the wrench monkies) and would also foul fairly easily. Fine-wires, on the otherhand, were a little more costly ($100 each; 12 spark plugs = $1,200) but never fouled, put out a much cleaner spark allowing for better engine performance at all altitudes, increased fuel economy and provided a much needed peace-of-mind that the plugs will perform in flight. Too much going on in a cockpit to have to worry about your plugs.

I've since discovered the same on my Sportster. Starts right up every time under every condition (hot or cold), performance seems better from dead stops shifting through all the gears into highway speeds, gas mileage is better (gained about another 1.5-2.0+ MPG), no fouling and that famous Harley exhaust sounds "Harlier." I paid about $10 for each plug. Pretty inexpensive mod with noticeable performance improvements. Check out Denso's website:

http://www.densoiridium.com

Quote:
Are they a regular brand at auto parts stores?
Yes and No.

Many auto parts stores carry Denso plugs but not the ones we need (IXU22 gapped at 0.040"). I bought mine from Dennis Kirk (had'em in a couple of days):

http://www.denniskirk.com

As for price, they're hardly what I would consider "expensive" ($10) especially when compared to aircraft fine-wires ($100 each) or when compared to all the extra chrome-crap people decorate their rides with and expect to get paid back for when they sell the bike.

Aircraft engines are not high-tech either, certainly not the standard air-cooled piston jobs commonly found in Cessnas and Pipers. In fact, isn't a Harley motorcycle engine just 2 cylinders of an aircraft engine?

 

It's called "indexing"...

 

K.. so you're not running a turbo, and the plug requirements for coil-on-plug are different than coil-wire-plug. With coil on plug, you are removing having to match the impedance of the output of the coil with the plug, with the plug wire. Plus, the Harley EFI system does ion-sensing for it's knock control settings. Basically it is sensing the 'impedance' between the electrodes of the plug. There have been posts, and I have not found anybody (at HD) to confirm, related to the point of non-standard plugs rendering the knock control system inop because of mismatched impedances. I do know you have to be careful what plug wires you use on the bike, because it will throw a DTC if you have improper wires. Although following that train of thought, a mis-matched plug should do the same thing, and I haven't heard of a mis-matched plug throwing a DTC....

 

This is the site that addresses Harley's knock sensing spark plugs. And, yes, some plug
wires (spiral core) will emit EMI / electromagnetic interference that can cause a variety
of problems. The SE wires are carbon core and the correct resistance to keep the
system balanced - not expensive either. IMHO.

 

[QUOTE=xxxflhrci;5505692]Spark Plugs for Evo Engine ('97 Wide Glide)

= Champion RA8HC

* I just change these out every 1,500 miles...cheap enough to do and clean plugs.

 

The HD plugs at my dealer were only about $3.50 each. They are made by Champion but are proprietary to H-D. They also have a specific resistance that provides feedback to the ECM via a tap on the ignition coil, for knock sensing purposes. Looks like cheap insurance to me!

 

[QUOTE=GREENOHAWK69;5514586]Changing plugs ever 1500 miles is a pure waste of good plugs.

 

wow. alot of Techno savy input for a SparkPlug. Lmfaoo, you guys are ACES.

 

>>Aircraft engines are not high-tech either, certainly not the standard air-cooled piston jobs commonly found in Cessnas and Pipers. In fact, isn't a Harley motorcycle engine just 2 cylinders of an aircraft engine?<<

More like a two cylinder slice out of an aircraft radial engine rather than the horizontally opposed flat motors that are in Cessnas and Beechcrafts.