What effect does changing the spark plug gap have?

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Jun 3, 2011 | 04:23 PM

#11

riteway

Extreme HDF Member

Joined: Apr 2008

Posts: 13,023

Likes: 989

From: Just Outside Chicago

Quote:

Originally Posted by fabrik8r

I've always been an advocate of indexing, it positions the ground strap so it doesn't shield the spark from the air/fuel charge.

My Brother was a 1/4 mile racer and did indexing but i never thought about it on my HD?... id like to see a pole on how many guys index their plugs and do they think it makes any difference.
If it really does help,seems like an ez performance improver!!!
Subscribed...

Thanks.... Tim...o~`o.....................................

Jun 3, 2011 | 04:34 PM

#12

mrfikser

Outstanding HDF Member

Joined: Oct 2009

Posts: 2,488

Likes: 30

From: Maryland near DC

I believe the difference in the specs. is for wear..say you are suppose to "be" between .038 and .044 ..you set it at .038 and as the plug is used the gap will expand with wear..when you reach .044 you need to regap the plug..but most people just toss them and install new long before that happens...That's my story and I'm sticking to it!!

Jun 3, 2011 | 05:03 PM

#13

dstrat1

Cruiser

Joined: Mar 2011

Posts: 228

Likes: 1

In the racing world, I first thing we see is guys buying more motor.(thinking it will make them faster)....My motor man took the money but told me ...Dave, the driver is worth seconds, the setup is worth tenths, the motor is worth hundreths (of a second)...One track day is worth more than most people can ever afford to do to their motor...... ditto for suspension...It is humbling to learn, but you usually are not slow because of the motor..

A little like talking to saleman in a high dollar (bicycle ) store about overweight customers spending an extra 1000 for a lightweigt bike and then hanging 4 water bottles on it.....

Last edited by dstrat1; Jun 3, 2011 at 05:06 PM.

Jun 3, 2011 | 05:30 PM

#14

jmacdonald5

Outstanding HDF Member

Joined: Nov 2006

Posts: 2,144

Likes: 10

From: Mass

..indexing plugs on an average Harley?....won't do anything to the engine, or performance that matters...no harm...but no point...to each his own...

Jun 3, 2011 | 05:45 PM

#15

speakerfritz

Road Warrior

Joined: Jun 2009

Posts: 1,943

Likes: 3

From: NYC

on an 07 ultra, changing away from stock plugs craps out the anti-knock feature, I tried plugs that were supposed to be gooder....but the loss of the anti-knock was anoying, so I went back to stock....I have to believe that change the gaps out of range could also bring havoc to the anti-knock system.

Jun 3, 2011 | 06:06 PM

#16

fireaxxe

Road Master

Joined: Nov 2009

Posts: 997

Likes: 3

From: Charlotte, N.C.

You want to set you gap close to the smallest setting for longevity. The tighter the gap the longer you can go between setting the gap the spark is strongest at the lower end of the measurement as the gap increases the spark is a little weaker because it has to travel a longer distance and this takes energy to accomplish. The smaller gap causes the spark to travel very fast and you want the spark to stick around long enough to ignite the fuel mix so if you go below the min setting you may have a misfire the same will happen if the gap is to large. I like to use the rocker arm shims to index my spark plugs they come in .005", .010", .015" and up to .025" I think they were originally used on the 80's model Shovel head engines and these are steel shims.

Nov 20, 2011 | 02:01 PM

#17

Jeff's 1st Harley

Road Master

Joined: Dec 2009

Posts: 1,118

Likes: 5

From: Coweta, Oklahoma

I tried gapping the plugs at .038 and thought it lacked the power it had before. I then regapped them at .043 along with indexing them and it seemed to run a little stronger than before. JMO.

Nov 20, 2011 | 02:50 PM

#18

SIDECAR BOB

Road Master

Joined: Jun 2009

Posts: 932

Likes: 14

From: CENTRAL IL

google Aunt tilly's spark plug gap guide by chris jacobs, he used to make on of the first electronic aftermarket ignitions for cars. it explains what larger and smaller gaps will do and the efect the have. Its based on v8 but woiuld be similar results in a v twin. not sure how big of effect it have but interesting reading all the same. couldnt get a good pic of the chart to attach sorry

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Nov 20, 2011 | 02:53 PM

#19

Gearhead3

Road Captain

Joined: Jan 2009

Posts: 739

Likes: 2

From: St. Louis

Quote:

Originally Posted by riteway

Thanks.... Tim...o~`o.....................................

I've done it to my RG and my LS1. I've also side gapped the plugs in both. It's cheap, it works, (you'll notice it more in some applications...not so much in others) plus I like to "tinker" with things. Hell, I run Mobil 1 synthetic in my push mower! (and yes, the plug is side gapped and indexed!!) I'm just a gearhead at heart and try to make IC engines run as efficiently as is possible. It's a disease.

Nov 20, 2011 | 03:08 PM

#20

NickD

Road Master

Joined: May 2007

Posts: 899

Likes: 10

I've always indexed my plugs. But I know it may be like hot chicken soup when you have the flu. It may not really improve things but it can't hurt and it does make you feel better . . .

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