Should indexed spark plugs face head or piston?? - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

Reply
 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 01-24-2005, 11:26 AM Thread Starter
 
Join Date: Oct 1999
Posts: 89
Thanks: 0
Thanked 0 Times in 0 Posts
 
Should indexed spark plugs face head or piston??

If you side gag and index your plugs which way should the gap face and in your opinion why is your way the best??

I know engines so we are talking best combustion angle.

Thanks
Doug
MudLake is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 01-24-2005, 11:55 AM
 
Join Date: Feb 2004
Posts: 946
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

The gap Towards the intake valve. I think the reason to index your plugs is to be sure the spark gap isn't shielded to the flow of the mixture coming into the cylinder.

I havn't heard of "side gapping" a plug but maybe it was called something else in my day.

OK. Found it:


Interesting idea. Must be a well kept secret as all the ignition books I've read has never mentioned it.

http://performanceunlimited.com/docu...degapping.html
John_Strenk is offline  
post #3 of (permalink) Old 01-24-2005, 12:18 PM
Carpal \'Tunnel
 
knifeboy2's Avatar
 
Join Date: Jul 2002
Location: Macomb, IL
Posts: 2,571
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

I've heard of it, and never put much thought into it, as I can't imagine it makes a noticable difference on my tired 304 running cheap pump gas.
knifeboy2 is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 01-24-2005, 02:01 PM
 
Join Date: Aug 2002
Posts: 353
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

I doubt that you will see much performance gain if you index spark plugs - usually only racers do it in order to squeeze every possible and miniscule amount of power
RedCJ7 is offline  
post #5 of (permalink) Old 01-24-2005, 03:36 PM
 
Join Date: Sep 1999
Posts: 2,006
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

[ QUOTE ]
usually only racers do it in order to squeeze every possible and miniscule amount of power

[/ QUOTE ]


Yep way back in the race car days we used about 6 sets of plugs to get the indexing right for 8 plugs,, and surprising as it may sound with competition fuel mixes it did make a difference. Small but it was noticeable on the scope. [img]images/graemlins/burnout.gif[/img]
GP'n is offline  
post #6 of (permalink) Old 01-25-2005, 12:08 AM
Journeyman
 
DuneCountry's Avatar
 
Join Date: Mar 2003
Location: Winchester Bay OR.
Posts: 134
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

We use "indexing washers" on our quads. They are different thicknesses to tighten up the plug in the right spot.
The gap pointed toward the intake port on a two cycle and toward the intake valve on a 4 cycle.
I have never indexed a car engine but I have seen the washer assortment somewhere, I think Summit Racing has them.
DuneCountry is offline  
post #7 of (permalink) Old 01-25-2005, 08:01 AM
 
Join Date: Dec 2001
Posts: 3,090
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

Waste of time and plugs!!!
did it to a mustang after a dyno run, and got NO differece on the second series of dyno passes.
BurnedBronco is offline  
post #8 of (permalink) Old 01-25-2005, 10:35 AM
Keyboard Implanted
 
Gnarly4X's Avatar
 
Join Date: Sep 1999
Location: Casa Grande, AZ
Posts: 3,758
Thanks: 0
Thanked 0 Times in 0 Posts
  
Re: Should indexed spark plugs face head or piston??

[ QUOTE ]
Waste of time and plugs!!!
did it to a mustang after a dyno run, and got NO differece on the second series of dyno passes.

[/ QUOTE ]

It depends. I know the guys at a local engine shop, they have an engine dyno and the chief engine builder builds mostly V-8s for drag racing, and he does index plugs with gap pointing towards the piston. In a daily driver or non-race applications you probably won't notice any difference.
Gnarls.
Gnarly4X is offline  
post #9 of (permalink) Old 01-25-2005, 12:35 PM
Way Outta Control
 
Join Date: Sep 1999
Location: usa
Posts: 10,815
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: Should indexed spark plugs face head or piston??

I've seen as much as about a 6% HP gain by indexing properly.
Most of the time you can tell where they should point by marking the ground electrode on NEW STOCK ORIGINAL PLUGS THE HEAD WAS DESIGNED TO USE - not aftermarket junk. And it must be torqued accurately to spec. That gives you the guide.

Then most of that time you'll find the open gap is toward the center of the combustion chamber. The ground electrode will be AWAY from the chamber's center.

The ground electrode creates a "shadow" to the flame. The flame has to bend around it, splitting the flame front into 2 waves as it passes. Sometimes when those 2 waves collide on the other side of the electrode it creates spark knock -- harmful ping. That's why sometimes they aren't always pointed directly at the center. In those cases the ideal place is found by experimentation.

Remember -- the intake valve closes long before the spark occurs. After the valve closes the gasses swirl and mix as it gets compressed. Just before ignition those gasses almost stop moving (it's designed to do that, the engineers aren't really crazy.) The spark ignites the mixture and the flame moves across the chamber evenly, creating a nice burn - hopefully without much swirling - you want a straight push down by the expansion.

That's why it's pointed toward the majority of the mixture - the center. (Same reason a Hemi works so well.

That's why multi electrode plugs are just a sales gimmick - too many shadows!
RRich is offline  
post #10 of (permalink) Old 01-25-2005, 01:56 PM
 
Join Date: Feb 2004
Posts: 946
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Should indexed spark plugs face head or piston??

Yeah, I should of thought the valve is closed for a long time.

But what about Side Gapping? Fact or Fancy?

Heck, I'm still trying to figure out how Ford put two plugs on each side of the combustion chamber and didn't create an area of intense pressure in the middle causing knock. Must of been the shape of the combustion chamber. [img]images/graemlins/smile.gif[/img] Must work because Audi and others are doing it.
John_Strenk is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome