How does the indexing tool work?

Larry
code5coupe

 

Well I want to gain 1%, for something this easy. What way should they go in a L98? I would think it would be the same for all like engines, but I could be wrong.

see ya on the road

 

It lets you screw the plug in with different washers to see where the ground strap will trun out? I don't think I'm going to bother doing this anymore.

 

 

The issue of clearance comes into play with high compression engines with big cams. My last engine (555 w/14 to 1 compression and a cam with over .800 lift) required the proper indexing of the plugs. The clearances are so tight that you could smack a plug into a piston at high rpm.
Also, flame travel in engines with big bores (mine was 4.56) needs all the help it can get. Flame travel gets more dificult in bores larger than 4.500. The sooner the plug can ignite the charge and begin the flame travel from one side of the cylinder to the other, the better.
There is also a realized HP benefit, but that's not why I did it.

 

Like this only more expensive.

 

That's what I'm thinking, too................................

I don't need the tool to do that, I only need the heads. The tool won't tell me where the straps will end up when the spark plugs are screwed into each of the eight holes in the heads.....

Larry
code5coupe

 

Spark plugs have no magic powers...they are simply a set of replaceable electrodes for the spark. The spark, in turn, simply initiates combustion...it either ignites the air/fuel mixture on the compression stroke or it doesn't. The spark cannot affect combustion speed, heat, or efficiency. Combustion chamber design (including piston crown shape) controls those things.

Larry
code5coupe

 

any increase in performance will be negated by the added weight of the indexing kit -

 

Well, yeah...and you are reconfiguring your combustion chamber.

Once in place, that spark plug tip is a part of the combustion chamber, just like the piston & valves.

Placing an obstruction between the spark and part of the mix DOES affect combustion speed, heat, and efficiency.

1% is still only 1% at the end of the day though. You either look at it like a big PITA for a street car, or a pretty cheap couple of HP.

Oh...to the OP...I don't have any clue how that indexing fixture works. I've always just used the Sharpie, like everyone else here.

 

Yes, it would be if that 1% figure was a fact.
So far, it has just been used as an example, not a proven fact.

You might look at it this way, also; If I understand indexing correctly, a spark plug's optimal position would have at least a 180 degree range in position. This means every spark plug, in every engine, has a 50-50 chance of being indexed correctly. In an eight-cylinder engine, four plugs will not require changing electrode position, on average. Makes ya' think, doesn't it?

As as been reported in this thread, by people who have tested plug indexing, it's more trouble than it's worth. People love it for the same reason they love K&N's; cheap and easy, even if the results are debatable.

I'll tell you this: if I knew for a fact that I could get 3hp by indexing my plugs, I'd do it tomorrow.
But, logic and other people's experience agree when they both say I'd be wasting my time and money.


That's just how I look at it.

Larry
code5coupe

 

A mechanic at a speed shop in which I had some involvement with ten years ago indexed the plugs for me and we dynoed the car not showing any gains at all. He was big into the bracket racing stuff with he and his buds indexing the plugs as standard fare.

That was ten years ago.......guess I could revisit it again as it may be worth another try just to see what happens.

 

I did this on my lawn mower and felt SOTP gains!

 

Well, the 1% was presented (in the other thread) as a statistical average observed by some well-respected engine builders on SBCs or SBC derivatives.

For an SBC the gap should be between the intake and exhaust valves, so the range is closer to maybe 60* than 180*. But it's largely irrelevant anyway, as the observed result is still the observed result regardless of how many plugs were involved, or how many happened to already be indexed by luck.

*Logic* says that the science is valid. The rest is subjective.

Maybe you'll change your plugs and lose 3hp next time.

We're splitting hairs here, though...at the end of the day most would consider ANY mod offering an imperceptible gain to be unworthy of ANY perceptible effort...

...and <5hp is imperceptible.

 

If that's a push mower, I call .

 

 

I must not have expressed myself very well.
If you look at the end of a spark plug, you'll see that the ground electrode only "shrouds" the center electrode (spark) for about 10 degrees of an arc; the remainder of the 360 degrees is "open"...the "gap" as you call it, is almost all the way around....there is only one very small area in which it is not open.

Logic would tell me that any spark plug... randomly installed... would have a 350 out of 360 chance of being indexed properly anyway. That's probably why the people reporting actual results on this thread say "no gain".


Well put.

Larry
code5coupe

 

I ran cut-back indexed plugs on my 85 at the dragstrip against an LT4 with normal plugs, and won.

So they're worth about 100 hp.

 

The issue though is the volume of air/fuel mix that is shrouded by that fixed 10* sector (or whatever it actually is).

With the strap down (away from the valves), the least volume of mix is shrouded from the spark.

Rotate it up, and that same 10* shrouds a much greater volume.

It's like casting shadow-puppets on a wall...if the wall is close, the shadow (sector shrouded from light) is small and well-defined. Move away from that wall and the shrouded area grows and becomes less defined.

Anyway, you get the idea. As you travel around that 360* circle, there's ~ 60* or so that the affected volume is minimized. That volume grows as you rotate the strap around approaching the center of the chamber, and shrinks again as it moves away.

Using 60* as a nominal estimate of the "best" arc to shroud (minimized volume), you have 300* that could be improved upon. This equates to an 83% (5/6) chance that any given spark plug could benefit. The actual degree of benefit is a function of actual strap position, combustion chamber shape, A/F ratio, type of fuel, blah, blah, blah.

What was it Smokey Yunick said...something about it being easier to find 100 places to pick up a couple HP than it is to find a couple places to pick up 100 HP?

For *me*, if there's 1% variance out there, and it costs a whopping $4 & 15 minutes per plug change (headers make it easy) to ensure that I have it...that's a pretty simple decision.

I've spent more time posting in this thread today than I'll spend indexing my plugs over the next 5 years.

 

Way too funny! How about your snow blower?