Spark Plug indexing

[836dstr]

Well, I just spent the afternoon indexing 4 sets of plugs. I thought the following information might be usefull.

This applies to 14 mm gasket type plugs. The crush thickness on the stock gaskets/washers ran between .050 and .055".

I bought a set of indexing washers packaged by Moroso (sold by Summit/Jegs/etc.). The set has 10 ea. .043", .054" & .064" washers for $15, or $.50 each. I found that this combo didn't give me enough selection to get the plugs deadnuts.

I went online to McMaster-Carr (http://www.mcmaster.com/) who I get a lot of fasteners and stuff from. I finally found metric 14 mm I.D. stainless steel washers that fit the bill:

1.0 mm    .039"  P/N 98089A392  $8.07 for 25 ea (as are all the packages)
.5 mm      .020"        98089A348  $6.52
.3 mm      .012"                  305  $8.14
.2 mm      .008"                  263  $8.26
.1 mm      .004"                  224  $7.35

This works out to $.31 each.

I found that a .5 mm and .2 mm washer/shim rotated the plug 180 degrees. The .5, .2 and .1 mm were the most usefull, but I did use some of the others.

Hope this is helpful for others.

Tom   

[jl222]

Well, I just spent the afternoon indexing 4 sets of plugs. I thought the following information might be usefull.

This applies to 14 mm gasket type plugs. The crush thickness on the stock gaskets/washers ran between .050 and .055".

I bought a set of indexing washers packaged by Moroso (sold by Summit/Jegs/etc.). The set has 10 ea. .043", .054" & .064" washers for $15, or $.50 each. I found that this combo didn't give me enough selection to get the plugs deadnuts.

I went online to McMaster-Carr (http://www.mcmaster.com/) who I get a lot of fasteners and stuff from. I finally found metric 14 mm I.D. stainless steel washers that fit the bill:

1.0 mm    .039"  P/N 98089A392  $8.07 for 25 ea (as are all the packages)
.5 mm      .020"        98089A348  $6.52
.3 mm      .012"                  305  $8.14
.2 mm      .008"                  263  $8.26
.1 mm      .004"                  224  $7.35

This works out to $.31 each.

I found that a .5 mm and .2 mm washer/shim rotated the plug 180 degrees. The .5, .2 and .1 mm were the most usefull, but I did use some of the others.

Hope this is helpful for others.

Tom   

  Thanks for the info, should be usefull to a lot of racer -tuners.

                        JL222

[sheribuchta]

on the harleys we only index the plugs it there is a large squish band --if your engine doesnt have a squish band you are wasting your time --you are much better off running duel plugs if you can --the flame front will start at both sides at the same time -faster flame travel =less timing and more horsepower --i guess that most of you car guys will have to be happy indexing the plugs which may or may not make more horsepower --if you have a lathe you can cut the bottom of the plug and you wont need any indexing washers   just some thoughts  willie buchta

[javajoe79]

 Good info. You can also run gapless plugs that don't need to be indexed. Though they might not be available for all applications.

[Loose Goose-Terry#1]

Many years ago I tested engines on the dyno using colder plugs, hotter plugs, side gap and gapless plugs. Wore out a couple engines just testing. But what the heck, the college furnished the dyno and the engines. Also tested the combinations that I thought worked best on dyno on the racetrack. Conclusion: indexing your plugs does about as much good as waxing your helmet

Good luck and have fun. Please remember, every time heat propagates to a surface and has to pass the air gap to another surface, you lose heat transfer and that will adversely affect the heat range of your plugs when you use several gaskets or shims.

Terry

[GH]

I always thought indexing plugs was like picking gnat s*** out of pepper.

[doug odom]

I think the problem is some people think indexing the plug is for horsepower. I have had to index plugs so they would not be hit by the piston. Now I was using a longer plug because it did make more power with the longer plug. But the indexing was done for clearance reasons in my case.

[jimmy six]

WE put together a dirt track 350 Chev with RHS iron heads 64cc chambers, 220 intake flow, and 11-1 pistons and had 6 plugs hit pistons. We used the reccommended  plugs and nothing hit on the hand turn over. It was a suprise but we have found this is common. Good Luck

[836dstr]

Thanks JD,

Wish you were going to be there.

Tom

[Dean Los Angeles]

Indexing spark plugs is like any other method you use to optimize horsepower. If you have a large squish area and the plug is indexed backwards the electrode is in the way of the supersonic wave traveling towards it.

Even if you don't have a large squish area, indexing the plugs makes sure you have uniform ignition in all cylinders.

In addition to washers, you can also buy 24 plugs, do a little mix-and-match to get the right ones out of the set, and return the rest to the store.

[ddahlgren]

JD next time try turning it over without the head gasket and without the washer on the plug.. Been there done that LOL
Dave