Spark Plug Gap

Hello,

I was wondering if anyone knows about, or has ever heard anything about
this: A co-worker of mine was looking on a site for tips for his Mazda
Miata, and I happened to see that the stock gap for their plugs is .044",
which is the same as my 1990 Honda Civic. Someone posted on the Mazda site
that reducing the gap to .035" gives you better combustion in the higher RPM
ranges. Is this true? If so, would there be any undesirable repercussions
in the low RPM ranges?

Thanx!

Jonathan

 

1. it may not start. the size of the spark gap is partly a function of
the gas pressure in the cylinder. the higher the pressure, the smaller
the gap can be. but on the very low cranking rpm's, cylinder
compression pressure is comparatively low, so you need sufficient gap to
spark properly.

2. when the engine's running under load, you need a big hot spark to
ensure full combustion. closing the gap means a smaller spark &
sometimes less complete combustion. back in the 70's in europe, some of
the ford rally cars experimented with dual spark plugs per cylinder
because of the increased engine output more sparking power provided.
the advent of electronic ignition that was able to get comparable power
by firing much bigger spark gaps reliably killed that idea. [plus of
course, two sets of [conventional] ignition systems are a pain to
configure & were not reliable in the way that electronic ignitions are.]

3. it effects the voltage spikes in the ignition coil which may lead to
breakdown over time.

4. regapping usually involves poking bits of metal around the plug gap.
it's been shown that small traces of metal left on the insulator from
this kind of activity can cause unanticipated sparking characteristics,
weakening the spark & causing less complete ignition, which in turn
causes emissions problems.

bottom line: always use new plugs with factory spec spark gap if you're
using factory ignition.

 

Don't experiment with various gaps--you could do some long term damage
that would be expensive to repair. Let your friend experiment all that he
wants with his Mazda--if that is what he wants to do. Use the factory
specs when setting gaps on your Honda Civic. You were wise to get our
advice. I made the mistake of experimenting with various stuff on my first
car--I learned the hard way that it is not a wise plan to experiment on
cars or motorcycles--I wasted a lot of money on my stupid experiments.

 

No. A smaller gap gives you a smaller, lower voltage spark. On a road car
with a coil and igniter expecting 1.1mm gaps, a smaller gap is not a good
idea.

Lower gas mileage, less power, etc etc etc.

Also, re-gapping platinum plugs can damage the platinum coating reducing
the lifespan of the plugs.

Just use what the manual tells you.

 

Thanx for everyone's feedback. I'll leave "well-enough" alone.

Jonathan