Consider keeping your stock factory plugs
but 'cut back' the ground electrode
and increase the gap to about 0.060
and sharpen all edges.
As you put the 16 plugs back in
'index' the gaps
so that the ground electrodes face one another
toward the center.
This allows the flame kernel to grow outward
from the FAQ:
On a 5.7Hemi, it is very probable that by re-arranging the stock 16 plugs to
their best position in other cylinders that is 'lucky for them' when they
tighten down, you could achieve indexing without buying more than
4-6 additional plugs at most....perhaps none at all.
My guess: Aim the dual plugs' ground posts each other (toward center of bore)
so the flame kernel can expand un-hindered outward. This leaves a small
spot in the center of the bore with a blocked flame path but it probably
won't matter because that spot is so turbulent anyway.
In the picture below the left hand sparkplug is the way I am talking about
but the right hand sparkplug needs to rotate clockwise another 90 degrees:
The factory stock ignition system that fires the dual plugs on the 5.7 is
apparently VERY good. Recently a few owners with high miles (68K and
108K) on original factory 5.7 sparkplugs have pulled them for inspection
and found these plugs are still firing with worn gaps as great as 0.075
This brings up the question of whether a 5.7 owner might want to pull his
plugs, sharpen all edges, then re-gap to 0.075 or more and do some MPG
testing to see if the dual larger sparks give enough 'fast burn' to improve
low rpm torque and fuel economy.
A DCx employee whose day job is running dynos reported that the stock
5.7 Hemi Ignition settings in the factory PCM is within 4 degrees of
'Mean Best Torque' at all throttle settings above 2000 rpm so it is not out
of reason that bigger gaps and sparkplug indexing could put you 'spot on'.