Im putting in new NGK v-power plugs this weeknd and they say to do them at .045 gap but on some forums for hemis' some people have said to gap them at .050 instead. Why? What would doing this do, would it increase performance or increase MPG any? I dont want my MPG to drop any by doing that.

 

You will still get a good spark to ignite the fuel. .045 or .050 shouldn't make that much diff.

 

The book says 0.045. Considering what it'll take to put 'em in an' take 'em back out, I'd suggest going by the book.

 

Why would you want to open the gap???

Curious minds need to know.

The fi guys either close the gap to 35 or go one range colder.

If you want to open the gap, just leave them in there for awhile, they will do it by themselves and throw some pretty cool check engine light codes.

 

+1, i would just leave it at .045

 

I cant add anything to that!

 

if you are willing to check them more often
{a considerably difficult task on the 5.7}
increasing the spark gap
and indexing the gap direction
will slightly advance the 'real world' ignition timing
and give a torque increase
particularly in the 1400 to 2400 rpm range
with less gain in the higher rpms

on another forum a guy who claimed to be
a Chrysler dyno test technician on 4.7 V8 (and former GM too)
stated that the 5.7 V8 was within 5 degrees
of what is called 'mean best torque timing'
on 87 octane gasoline
so the potential of a wider spark gap is not huge.
that makes sense considering the dual sparkplugs.

the general idea is that you want to increase the spark gap
to the maximum before miss-fire rate increases
at the toughest condition...70% MAP at high EGR flow at 3000+ rpm,
then back off on the installed gap on a new plug
giving the gap room to naturally 'grow' until it reaches the
miss-fire gap size at the recommended service interval
like 30,000 miles, etc

using one of the irridium or gold alloy tipped sparkplugs
that essentially do away with spark gap growth
is worth considering if you intend to increase gap
and don't want to re-check often

the Toyota 4.7 and 5.7 V8s have been using irridium tipped plugs
and wider gaps for some time now

for forced induction (super or turbo charged)
you do want to reduce spark plug gap
to reduce miss-fires
because the consequences of a missfire
can lead to severe detonation on the next cycle