Gents, dealing with RHS Pro-Action aluminum heads and the 3/4 reach Champion C57YC plugs they recommend. the plugs out of the box are gap'd @ .025. I am running HEI w 50kv coil. I previously understood that with HEI plug gap should be ~.045 but there is no way to put that much gap on these plugs. Even increasing to .035 requires some force and then the electrode angle looks fubar?! I am leaning towards installing them out of the box but that I would look for some feedback.
TIA!

 

Autolite platinum AP3924 They are the best heat range and use a thin coat of antiseize

 

.045 is commonly used. I use .050 with the ground straps cut back to expose greater portion of air/fuel mixture to the spark. Looks like this;

http://www.google.com/imgres?client=...6&tx=138&ty=67


Then the angle of the ground strap is not a concern.

 

You need to get a pair of plug gapping pliers. Holds the plug with the gap of your choice and when you squeeze the handles, they make the ground strap parallel to the tip of the electrode just like it should be. I got mine from Summit.

 

I'd call RHS tech and question them on the recommended gap. That seems way to small to get an efficient spark imo.

 

Been using those since the 90s never ever had a bad one.
(oops edit non platinum)
3923 if you need a little colder one

Run .035 with an MSD never saw need for a huge gap.

 

After I installed new plugs AC45, new HEI dist. And 50000V coil I had a miss fire at idle and at low speed. The last thing I checked was my plug gap because they were new plugs and I had gapped them at .045 when I installed them. But I must have have used the wrong feeler gage because they were only gapped at .025. After correcting the gap back to .045 the moss fire or popping sound was gone.

 

They look like normal Champion plugs see no reason why they cannt be adjusted to .045

http://dragpartsusa.com/i-10814716-c...FUie4AodJAsAIQ

 

Thanks guys! After thinking through this a little more I re-evaluated and using a standard feeler gauge and my vice as a force point, I was able to get a clean, square 040. Installed them last night while watching the ballgame. I did use light anti-seize on the threads and di-grease on the termianls.

I know lots of folks like Autolite plugs....but I have been using Champions for long time and comfortable with them. RHS/COMP recommend either these for street or ZEX for track, but they do not recommend gap as they claim it is dependent on the type of ignition system. Maybe I'll try the Autolite next time, but it kinda gives me the *****'s to put Ford parts in my Chevy... and I know the affiliation with Ford is long gone, but still....

I do find it strange these came 025 out of the box. Iv'e never used a MSD multi-spark type system, is this a gap taylored there?

anyhoo, thanks for all the advice!

 

I do find it strange these came 025 out of the box. Iv'e never used a MSD multi-spark type system, is this a gap taylored there?


In the instructions for the MSD 6AL ignition box, there is a chart for spark plug gap versus compression ratio. For up to 10.5CR, the gap can be between 0.050" - 0.060", for 10.5 - 13.0, gap is between 0.040" - 0.050", above 13.0CR, gap is 0.035" - 0.045". I'm at 11:1, so I've been running 0.045".

 

I always run as big a gap as the system can tolerate without misfire.
Bigger spark better light off.
Better light off, better throttle response and more time to burn all the fuel which equates to more potential power and better fuel economy.

 

Well that answers that! Like I said I set them at 040 I am running 10.5:1 compression. Installed the plugs, set the timing curve and adjusted the carb. Went out for short ride this morning and everything is great! Nice smooth idle @850, good throttle response in a short cruise with light acceleration. I'll go out tomorrow morning when the roads are clear of morons and go for a romp but for the moment all is good! Thanks again for the advice!

 

Just to throw a wrench into the wide gap theory. I run NGK -9 heat range plugs gapped at .025.

Ill close with this... You ever notice the gap the plugs come with in the box, the gap the plugs are manufactured with? It gets smaller as the heat range gets colder. If you are using the right heat range, the gap is appropriate for the cylinder pressure. They have been making sparkplugs a long time, you might think they have the gap deal figured out.

 

There are many factors that determine what heat range you run and what plug gap you run. What the manufacturer guesses for your application (how could they possibly know what you are using it in or in what application) I would not consider one of those factors.
However; CR, intake temps, fuel volatility, chamber turbulance, squish distance, detonation resistance, RPM, ignition system voltage, etc. those are the just some of the factors that should be considered.
Think of it like this. If you have ever used a gas stove with piezoelectric ignitors how many clicks do you hear before the flame is ignited? At least two or three, usually more, that's a very small ignition source. With an old gas stove how many matches does it take to light the gas? likely one. That is a relatively large ignition source.
Same with a BBQ. Those piezoelectric ignitors. You'll push that thing half a dozen times some times and still not get the gas to light. Use a match and it lights right off. Better yet use a torch. At some point a larger source is not better just larger. But too small of a source of ignition delays the complete burn of the fuel.

The fuel only has X amount of time to burn. The conditions in the combustion chamber are not always ideal for ignition. We try to achieve that, but fact is many factors can alter our carefully planed combustion process.
If the fuel does not burn quickly enough then some of that fuel is left unburnt. That unburnt fuel or not completely burnt fuel goes out the exhaust pipe wasted and not producing power.
So in order to give the fuel the best light off and the best chance of burning completely it seems it would be of benefit to have a nice large, hot spark with the greatest exposure to the most mixture. Particuarly at idle and lower rpm operations due to lower CR's from overlap on the cam.
At higher rpms if the ignition system is not up to the task then the gap will need to be closed in order to get a strong enough spark to prevent misfire.
Check out the plug gap on your modern fuel injected car. Chances are it's .050 or bigger. Many are of a fine wire construction. This is to focus the energy of the spark creating a hotter spark for good ignition, and to expose more of the mixture to the spark.
At the end of the day the difference is small, but still notable. For those wanting a fine tune it's worth consideration.