HarleyTechTalk

Harley Davidson has the new Irridium Screaming Eagle spark plugs in a few different flavors and I was wondering why the high compression version has a gap of .035. I was also wondering what they considedered "high compression" and what the theory was in closing the gap to .035 instead of .040. It would be interesting to find out the diference in the standaard plug compared to the high compression plug other than the obvious gap difference.

Quote from: greg1140 on November 07, 2009, 03:28:22 PMIt would be interesting to find out the diference in the standaard plug compared to the high compression plug other than the obvious gap difference.

Probably @ $10-15 per plug... LOL.

You are close, they are $16 a pair and are suposed to be Irridium plugs. I just want to know the difference in the standard Irridium harley plug and the high compression harley Irridium plug. The price is the same.

Quote from: greg1140 on November 07, 2009, 05:26:24 PMI just want to know the difference in the standard Irridium harley plug and the high compression harley Irridium plug. The price is the same.

Different heat range

Higher compression has smaller gap to control spark in a higher pressurized environment.  I would simply stick with the stock plugs.

search more here and with google about plugs - unless your in the 150HP+ area the so called performance plugs are snake oil.
...gene

the higher the density of the air on the chambers, the more pressure (voltage) required to combust, which also requires sometime to reduce the gap to allow the spark to jump in high density air. 

Quote from: genedjr on November 07, 2009, 10:49:08 PM
search more here and with google about plugs - unless your in the 150HP+ area the so called performance plugs are snake oil.
...gene

I was told the same thing by my parts guy.

Quote
........  I would simply stick with the stock plugs.

I am not running out to get them

I have done too much plug testing over the years and even though I am not a Champion fan I run stock and will stay with them. Really if the stock plug needed to be gapped down because of a miss at higher rpm (higher voltage demand less time to build up voltage compounded by high compression) I would be looking at a higher output coil and try to retain the wider gap. That said these motors are low rpm relatively speaking and a warmed over car motor turns higher.
Irridium, an invention to satisfy maintenance requirements when passing stringent EPA emission tests for component durability IMO, now being touted as a performance enhancement?
I hope HD has got the resistance right with these new plugs and if so I expect the owners will feel good and the dealers will too but the net result is a more durable plug, that's it. That said when a motor is tuned right the stock plugs are very durable and cheap. Just throw a set in every 10k and even then the old ones don't look too bad high compression or not unless the motor is detonated and that will kill any plug.

really am I missing something? I know I am an antique but why do we need these and what will they offer?

Build a better mousetrap ...

It gives the mice something to laugh about and fills the wallet of the marketer.

Iridium plugs have the potential for longer life. But even a stock plug or equivilant will last far longer than most give them credit for. Same goes for lifters, these aren't Shovels, Pans or Evos. While the TC still places more stress on some things than an automotive engine, many are replacing things long before they actually need it.

Do whatever makes you feel comfortable or can afford. A little tighter gap on a high compression motor may help ... may not. Most modern electronic ignitions have more than enough voltage and current capability to handle even the nastiest street driven HD.

EDIT: Forgot to mention that many Iridium and other fine wire electrode plugs come pre-gapped due to the fact that they are easily damaged if not gapped with the proper "finesse". It's likely that the gap is tighter on the "Hi-po" plug because they figured that most would attempt to tighten the gap to make it "better" and ruin the plug.

Quote from: ederdelyi on November 08, 2009, 06:59:57 AM
Build a better mousetrap ...

It gives the mice something to laugh about and fills the wallet of the marketer.

Iridium plugs have the potential for longer life. But even a stock plug or equivilant will last far longer than most give them credit for. Same goes for lifters, these aren't Shovels, Pans or Evos. While the TC still places more stress on some things than an automotive engine, many are replacing things long before they actually need it.

Do whatever makes you feel comfortable or can afford. A little tighter gap on a high compression motor may help ... may not. Most modern electronic ignitions have more than enough voltage and current capability to handle even the nastiest street driven HD.

EDIT: Forgot to mention that many Iridium and other fine wire electrode plugs come pre-gapped due to the fact that they are easily damaged if not gapped with the proper "finesse". It's likely that the gap is tighter on the "Hi-po" plug because they figured that most would attempt to tighten the gap to make it "better" and ruin the plug.

I have tried HD's high compression heat range plugs before, on a 10.5:1 bike. Ran like crap. Stick to stock heat range for sure. Also tried their splitfire, platnum split fire and every other thing they have put out as a plug. I like the narrow tips on the hi performance plugs or I would stick with stock. I carry a pair of stock ones on long  (1000+ mile) trips, just incase. Have never needed to change them on the road, except when using the high compression heat range. They would carbon up after a day and run bad.