Spark Plug Gap Thoughts


Installed the Edelbrock Performer RPM aluminum heads #60179 designed for the 68-73 340 engines onto my newly rebuilt "close to stock" specs 1970 340 engine.

Engine was bored 30 over as a clean up with new pistons

Initial start will be with points ignition

Edelbrock recommends the use of Champion RC12YC spark plugs with these heads.

No recommendation on spark plug gap. Purchased the plugs; I was going to gap at the usual .035.

Any thoughts on this appreciated.
Phil

With points I would use .030 and change it later with a better ignition to what the new ignition calls for

anywhere in the .030-.035 range should work ok.

Agreed, with a lean towards .030 if all is stock

Buy Autolite 3924 instead. They will be gapped a 44 so close um up 32-35

Spark plug recommendations are like oil, filters, and so many other things; opinions vary.

If you already have the Champs, there is no good reason not to go ahead and run them. Especially on a milder build. If you feel that they do not last long enough, you can always change brands later if you feel the need to experiment.

I have ran both the Champs and the Autolites in my Hemi. I haven't noted any difference between them.

And .030" to .035" would be a good range. If the Champs come out on either end of that, I would just run the gap that they were sent with.

I don't have a problem with .035" gap on my 51 Plymouth's points ignition. It ought to work just fine.

Is it converted to 12 Volts or still the stock 6 volt ignition system?

12v now, pretty much mimics the OP's setup. But even when 6v it had no issues at .035"

Engine Masters did a stint on plug gaps.Sdeems with good ignition they actually gained power and torque.This was on the dyno usins different plugs.I run 45 to 50 thou on my aluminum headed 440 with MSD.

The difference wasn't as much as you'd think. 2hp on an 800hp engine, 0.045 vs 0..065"

They also did one on ignition, Best one was with a MSD box.

Do yourself a favor and get NGK plugs. Champions have too much resistance.

Not being argumentative, but Champions have too much resistance for what?

I have tried all 3 preferred brands in my engines; Autolites, NGKs, and Champions. I have experienced no difference in them. Just like oil, filters, carbs and so many other products, it seems that some guys have better experiences with one brand over another. But that does not mean that the other brands are inferior or no good.

How about some evidence of the additional resistance that the Champions have and the results of it that you feel would negatively impact the OP in his relatively mild engine?

When you say they, Champions, have too much resistance what are you talking about, from the tip on top of the plug where the plug wires slides on to the bottom of the center electrode or exactly what?
You do know that the coil will only build up enough voltage to jump the easiest gap, correct. The easiest gap to jump, correct? It will jump out of bad wire to ground or jump around inside a dirty distributor cap, correct
Try setting all of the spark plug gaps at .035 and then go drive the vehicle, come back and regap them all to .045 and then go drive it again the same way on the same route and let me know what you found different and like or didn't like about the wider gap or smaller gap
Back in the mid 1970s when MSD was still building and selling their first gold race boxes, 404,404B and 404C, I used one of them on my old max wedge stocker with the plug gaps set at .090 per their instructions, we didn't get the same information on time slips back then, 1/4 mile ET and MPH only. I later try narrowing the gap to .045 and then down to .035, I never saw a noticeable difference in the time slips or how the car started and ran in gear around the pits and on the race track.
I did see a noticeable difference on my other stocker I race from 1974 to mid 1976in my old 1970 Hemi Cuda, it started and idle better when cold, below 45F in the winters in the high desert in SO CA, that car liked those old gold MSD race boxes and so did I
It would also pull in high gear in the middle of the summer in SO CA at the old Irwindale 1/4 mile track back when you could cut the smog with a knife, it didn't do that well with either the old Hays S4 ECU, later became Stinger brand ignitions and the old Mopar D.C. Chrome race box ECU

I've never had an issue with new plugs gapped at .035 on any street driven car I've ever had (that called for an.035 plug gap). The gap gets larger as the plugs add on the miles. I have pulled older plugs and re-gapped them back to .035 and the ride seemed to run better, but that was probably just my mind playing games with me.

Larger plug gaps can cause problems with first start ups in areas with cold winter temps, especially with standard ignition systems.