My application on a 383 is with Autolite AR72, they already have the ground electrode cut back, car seems to run better

may be worthless on the street,I feel good doing it even though I run junk

I have cut the strap back also,only thing I got out of it was change the plugs more often,even split the ends like the splitfire plugs

home hawg porting the heads,gasket/port matching every thing down to drilling the oil pump to 1/2 and port matching it to the main cap all gave me good results,some better than others

it has been noticable to me after indexing, wont know till ya mojo,

thats my hobby anyways, homeporting/grinding and doing all the mods I can to make each one with my own mojo,how else am I gonna learn

I even bumped up the exhast valve in a #302 head to 1.60 and just hawged out the exhast port and left the rest untouched and added headers and got a gain in performance on a stock engine

why?,thats what I thought porting was about,getting the exhast to flow as close to the #s of the intake port as possiable,IMO it helped it and was worth the labor for free HP

the time spent hand massaging the engine is free performance with longevity

result may vary and often do,IMO

maybe its just me being rabid under the shade tree doin my hickabilly thing

self skoolin,runin junk,havin a good time,keepin the jy open stimulating the economy buying gaskets

runwhatyabrung

From NGK site: (Still doesn't answer the question)

This is for racers only !!
Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.

However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.

In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.

translated...results may vary

starting out with 150 HP,I will take every 1 HP I can get for some free laobor

Here's the best thing I've found so far:

According to Dr. Christopher Jacobs (of Omni-Pak and Pro-Street ignitions from Jacobs Electronics), indexing sparkplugs 'never hurts and sometimes helps'. Indexing is especially useful if the combustion chamber has a 'squish' area where the piston almost touches the head. This squish area 'squirts' a high speed flow of mixture toward the spark plug. The Dodge Magnum heads do have a squish area (also sometimes called a quench area). The spark plug is at the 'outside' (toward the fender) of the head and the spark plug hole is angled toward the exhaust valve. The intake and exhaust valves are in the middle of the chamber. The squish area is 'inside' toward the intake manifold. The combustion chamber is not round. It is 'kidney' shaped with the tip of the indented 'v' of the kidney pointing toward the spark plug. The difference between 'round' and 'kidney' is the 'squish area' where the piston top almost hits the head at top dead center.
For indexing, Christopher Jacobs recommends that you mark the insulator of the sparkplug with a black magic marker (not a pencil as graphite conducts electricity). Draw a line on the insulator on the side where the gap is open - opposite the side where the ground electrode is. Seems like you could also scratch/grind a mark on the top metal electrical terminal so that you could see & feel it. To align the spark plug's open gap toward the quench area, you would need to have the marked line on the 'top' side - away from the fender on that side of the truck. If you are looking down on the installed sparkplug, this means the mark should lie at either 11 o'clock (if the plug went in angling slightly toward the front of the truck) or at 1 o'clock (if the plug went in angling slightly toward the rear of the truck).
In practical terms, any o'clock position between 10 o'clock and 2 o'clock would be in the ballpark. This would also mean that if the open gap's mark lay in positions between 4 o'clock and 8 o'clock it might be bad - the ground electrode would stand like a fence post partially blocking the spark gap from the squish area.
Jacobs sells washers to go onto the sparkplug's seat to cause the plug to line up this way. You can also file off a little bit at a time of the start of the first thread to cause the sparkplug to end up turned a little. If you have a lathe you could turn off just a bit of the seat.

best thing yet,like i thought,I had the wedge thing backwards..it lights from the big side wedging across the piston to the quench side for leverage

and good quench,happens very fast and can actualy cool the air/fuel charge some for better ignition of the fuel.IIRC

and yes the angle of the plug and 10 to 2 "o-clock" would be in the ball park

worth checking any head IMO

just making sure the flame is not blocked on 1 cly or more per head would be a good thing,IMO

So what thickness wahsers are we using to subtract degress?

Where can I find them?

I index mine in the cuda...906 iron heads{oversized valves} on the 440...I run them straight up at 12:oclock position...They definitely look much cleaner and the "shadow" from the electrode is gone in this position...I have the index washers but I usually just buy a bunch of plugs then sort them out so I don't need to use them... ..I'm right around 500 HP and it seems to idle/run better with them indexed...FWIW..