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 Post subject: Indexing Spark Plugs?
 Post Posted: Tue Sep 22, 2009 10:31 am 
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OK, how many of you are doing this and if so, what (if any) advantage have you seen?

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 Post Posted: Tue Sep 22, 2009 11:32 am 
 
I do but i have no choice if i don't they will hit the pistons.
don't know how much if any advantage to it on some of my other engines i did index them and had to change them at the track and didn't have time to index them and the car ran the same so i guess it depends on your engine combo if there is any advantage to it or not just no my junk.


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 Post Posted: Tue Sep 22, 2009 12:20 pm 
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I dont know if it makes any difference but I do it on all mine no matter what, started doing it a few years back when I had no choice but to do it.

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 Post Posted: Tue Sep 22, 2009 2:18 pm 
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I have to index mine for piston clearance too. I don't think there's any performance advantage to it other than mine runs better if the gap isn't closed ;-)

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 Post Posted: Tue Sep 22, 2009 4:37 pm 
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I have indexed plugs on engines that didnt need it for clearance reasons. I observed improvements in the burn. It's not an obvious sign but the engines run smoother . You have to be really careful and sensitive to these things and have the equipment necessary to pick it up.
There is plenty of evidence around that you can find on the internet with Kirlian pictures of pressure progression from the flame kernel, and its always the same, the strap slows the pressure growth in that area. All scientific papers I have read about the subject arrive at the same conclusion too. When the engine is reliant upon efficient flame kernel formation it would make the most difference and the engines I have had to do it on were problem ones.
I must say that if the engine has good fuel preparation techniques and the optimum fuel in it then indexing for non clearance reasons is an undetectable benefit. Thats just what I see in the real world. But my advice is to always index plugs, it doesnt detract, it can only benefit.


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 Post Posted: Tue Sep 22, 2009 4:51 pm 
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So where do you index the ground strap too? I've seen towards the exhaust valve, and so the open side is facing down. What do you all use?


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 Post Posted: Tue Sep 22, 2009 5:04 pm 
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ron owens wrote:
I do but i have no choice if i don't they will hit the pistons.
don't know how much if any advantage to it on some of my other engines i did index them and had to change them at the track and didn't have time to index them and the car ran the same so i guess it depends on your engine combo if there is any advantage to it or not just no my junk.




X2 =;

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 Post Posted: Tue Sep 22, 2009 8:35 pm 
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For flame kernel reasons index the plug so the strap is at the top of the chamber. It depends a bit on the style of head. small variations in plug orientation are not detectable differences.


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 Post Posted: Wed Sep 23, 2009 12:53 am 
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Do I? Yes!
Advantage? Spark plugs stay open! [-o<

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 Post Posted: Wed Sep 23, 2009 3:16 pm 
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Beretta wrote:
ron owens wrote:
I do but i have no choice if i don't they will hit the pistons.
don't know how much if any advantage to it on some of my other engines i did index them and had to change them at the track and didn't have time to index them and the car ran the same so i guess it depends on your engine combo if there is any advantage to it or not just no my junk.




X2 =;



X3 well X4 if I get one for both cars

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 Post Posted: Thu Sep 24, 2009 4:48 pm 
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Sounds like some of you need to take 1/2 an hour with a sanding roll bext time your heads are off and put a slight indentation in each piston. =;


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 Post Posted: Thu Sep 24, 2009 11:27 pm 
 
Mine does have them in there from Aries just not enough.


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 Post Posted: Sat Sep 26, 2009 4:04 pm 
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Mine also have a relief which has been modified for flame travel, its the side of the dome that closes mine up, two cylinders have to be done..


and the digger uses long reach plugs in a short reach head, to relieve them I'd be through the dome

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 Post Posted: Sat Sep 26, 2009 10:50 pm 
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Both my aluminum head SBCs (one Dart, the other Brodix) use long reach (.750) 14mm plugs and neither has a problem with pistons hitting them. Reason I started this thread is because the last set I put in didn't get indexed and was wondering whether others has seen a performance gain from indexing.

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 Post Posted: Sun Sep 27, 2009 2:16 am 
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Seems like I did some dyno testing on this very thing about 12 years ago. Indexed them both ways,...electrode up and down. As feeble memory serves me...I don't think it made a bit of difference.

I think indexing the plugs came into vogue back in the Modified Eliminator days when there was a weight to cubic inch rule in place. In the smaller inch engines you had to have everything running on the minimun to get any compression. They had to make sure the pistons were not at or near TDC in order to just install the plugs or they would risk breaking off the electrodes. The shop I grew up around use to take body filler and mock up the domes of the pistons. Then send them off to the piston manufacturer to have them made. After that they would still massage them into their final shapes. This was back when "Hank the Crank" was D-stroking 283 cranks and they would twist them up to 12k RPMs or so.

Now that I think of it though,...I don't think I did any testing like this on anything that had a bore size over 4.375. So it may make some differences in the higher rpm engines with 4.6"-4.7" bore sizes.

Don

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