gap for plugs - MSD box & dist.

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str12-340

str12-340

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I am going over my 340 and wanted to get the best pugs and the correct gap for my set up. This is a 1969 340 with factory TA heads and forged nominal 10.5:1 pistons (my best guess is between 10 and 9.5 to 1 actual compression). The car is street driven with very few passes down the 1/4 mile. The ignition set up is an old analog MSD 6A box and a MSD billet distributor with a Flamethrower conventional shaped coil. The engine is running well on Champion RN14YC plugs, but it is time to replace them and there is a lot of new technology out there. The main goal is rock solid dependability - can't have things screwing up hundreds of miles from home. The RN14YC plugs were gapped at .045.

Looking for replacement plug recommendations and gap recommendations with the MSD set up.
 
There is no new technology in plugs. .045 is the widest gap I’d go. The plugs you have are fine. Just replace with the same.
 
I’ve gone further on a driver. A stock low compression 360 looking for mileage. When the gap was at .055, it fell off some and I went back to .050. This is what I found best for THAT APPLICATION which may it be good for YOUR APPLICATION.

With the higher compression ratio, the gap needs to be smaller. IMO, that .045 is correct and what I’d run and do run as well.

Same spark plug by the way.

I also have no issues with Champions. Others like Autolights a lot. Some claim they last longer in the race or hotrod. I’d just run what ya got. No trick plugs needed.
 
I would go 45 and go with the Champion or Autolite
Last set of Autolite or Champion I used were set at 44 out the box. So just checked all to make sure all were at 44 and ran them
 
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And the gap will widen as they wear.
 
str12-340 said:
I am going over my 340 and wanted to get the best pugs and the correct gap for my set up. This is a 1969 340 with factory TA heads and forged nominal 10.5:1 pistons (my best guess is between 10 and 9.5 to 1 actual compression). The car is street driven with very few passes down the 1/4 mile. The ignition set up is an old analog MSD 6A box and a MSD billet distributor with a Flamethrower conventional shaped coil. The engine is running well on Champion RN14YC plugs, but it is time to replace them and there is a lot of new technology out there. The main goal is rock solid dependability - can't have things screwing up hundreds of miles from home. The RN14YC plugs were gapped at .045.

Looking for replacement plug recommendations and gap recommendations with the MSD set up.
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Check out MSD's website. They have a chart on spark plugs and gaps. Start with whatever they recommend and go from there. On my 408, I am running NGK's gapped to .043 with an MSD 7AL3 and Pro Billet distributor.
 
The statement in post #2 is completely wrong, there is NEW technology. The writing mannerisms remind me of someone that has been banned from this site at least twice before....


Platinum, Iridium are just two of the new boys on the block.
The plug you are using is a hott-ish plug which is a good idea. NGK equivalent is a 5.

If you go to a Plat or Irid plug, you get two major benefits: long term reliability & higher spark energy which allows you to run a bigger gap. The smaller electrodes of P & I plugs require less firing voltage, which means they can run bigger gaps. The benefit of a bigger gap, exposing more spark to the mixture should be obvious. With a canister coil, I would use 0.055" gap, 0.060" gap with a an E core ign coil. MSD actually recommends 0.060" gaps up to 10.5:1 CR with the 6A box, & that is with stock coils & stock spark plugs.
 
Bewy said:
The benefit of a bigger gap, exposing more spark to the mixture should be obvious.
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It's not the size of the spark, it's the quality of the spark. I find .028-.030 works best for me in most cases.
 
Bewy said:
The statement in post #2 is completely wrong, there is NEW technology. The writing mannerisms remind me of someone that has been banned from this site at least twice before....


Platinum, Iridium are just two of the new boys on the block.
The plug you are using is a hott-ish plug which is a good idea. NGK equivalent is a 5.

If you go to a Plat or Irid plug, you get two major benefits: long term reliability & higher spark energy which allows you to run a bigger gap. The smaller electrodes of P & I plugs require less firing voltage, which means they can run bigger gaps. The benefit of a bigger gap, exposing more spark to the mixture should be obvious. With a canister coil, I would use 0.055" gap, 0.060" gap with a an E core ign coil. MSD actually recommends 0.060" gaps up to 10.5:1 CR with the 6A box, & that is with stock coils & stock spark plugs.
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It’s not new. Those plugs have been out for years. The REM plugs are designed for engines that the manufacturers want to go 100k miles before they need to be changed.

They can lose power, especially if the ignition is under powered. What the OP has and is doing is perfectly fine.

It’s dumb to use those plugs if you can get to them. It’s not a performance upgrade.
 
More BS in post #13. My Dart had the same type of Champion plugs [ post #1 ] when I bought it in 1969.
Decades ago. My 1996 only lists Plat plugs, not Iridium not available at that stage. Plat plugs were also pretty new on the block. I picked up the flier [ below ] on the new Irid plugs in 2004. My 1993, 850 page Bosch handbook does not mention Plat plugs.

img328.jpg
 
Newbomb Turk said:
It’s not new. Those plugs have been out for years. The REM plugs are designed for engines that the manufacturers want to go 100k miles before they need to be changed.

They can lose power, especially if the ignition is under powered. What the OP has and is doing is perfectly fine.

It’s dumb to use those plugs if you can get to them. It’s not a performance upgrade.
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Years? How bout decades? Especially Platinums. When you said no new technology, I immediately knew you meant the likes of Splitfire, E3 and all that "snake oil" and you're dead right. There ain't any new plug technology. You gave good advice.
 
Completely wrong. If it hadn't been for 'snake oil' we would still be using two piece 18mm spark plugs that my 1942 Harley had. Just one example of many. The Copper centre electrode is another......
 
Engine masters already did the episode comparing spark plugs. Short version: doesn't matter when it comes to power output.

Platniums run hotter, iridium are harder, copper are cheap and work. Outside of more complex systems like mazdas skyactiv and similar, there's no new tech in spark plugs the last 35+ years..

The extra heat of the platinum helps them avoid fouling and last longer between changes and their adoption was more to keep up with EPA fuel consumption targets for more miles.
 
Bewy said:
Completely wrong. If it hadn't been for 'snake oil' we would still be using two piece 18mm spark plugs that my 1942 Harley had. Just one example of many. The Copper centre electrode is another......
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blah blah.....I hear a toilet flushing backwards in the background. lol
 
Phreakish said:
Engine masters already did the episode comparing spark plugs. Short version: doesn't matter when it comes to power output.

Platniums run hotter, iridium are harder, copper are cheap and work. Outside of more complex systems like mazdas skyactiv and similar, there's no new tech in spark plugs the last 35+ years..

The extra heat of the platinum helps them avoid fouling and last longer between changes and their adoption was more to keep up with EPA fuel consumption targets for more miles.
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Didn't they also conclude copper was the best conductor? I know it was found to be true I just caint remember who did it.
 
RustyRatRod said:
Didn't they also conclude copper was the best conductor? I know it was found to be true I just caint remember who did it.
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Best, depending on how that is qualified. There are better, but they cost a lot and the difference isn't really enough to justify it. Most copper electrodes are alloyed with nickel for heat resistance.

Even aircraft engines which operate almost exclusively under constant and immense load use copper-nickel plugs.

I've had a few vehicles that came OEM with iridium plugs and the Mfg in each instance acknlowdged it was because of the increase chance of fouling and not performance or power which required their use. One was a Honda big twin motorcycle with dual plugs, but it was a big bore and the plugs were so far from center that they collected carbon no matter what the AFR was. The others were boxer engines that dealt with higher oil consumption.

I did some reading on plugs that lead me to run platinum ones in my dart, but I really haven't noticed anything. The thing that got me curious was the firing voltage for a platinum is supposed to be lower and so less chance of misfire. But the more reading revealed that the lower breakdown voltage isn't actually a benefit because less energy is actually jumped across the gap and in very rare instances there can be secondary spikes and other electrical black magic that can nuke sensitive ignition electronics (which our cars don't have, but some late model and especially exotic ones do) which is why OEMs are such sticklers for using the exact right parts.
 
The 'copper' seems to always confuse people.......My understanding is that ALL of the major manufacturers use copper. The copper is not exposed directly to engine heat which is why it doesn't melt. It is encased in a steel compound in the centre electrode.

The performance benefit with Plat, Irid comes from being able to run bigger plug gaps because the reduced firing voltage allows this. Common sense should tell you that the bigger the spark, the better......& more chance of complete combustion.

That big cam you fitted & now idles rough. That rough idle is incomplete combustion & the engine misfiring. I wonder if you had a spark 1/2-1" long.....& hotter....what would it do.
 
Bewy said:
The 'copper' seems to always confuse people.......My understanding is that ALL of the major manufacturers use copper. The copper is not exposed directly to engine heat which is why it doesn't melt. It is encased in a steel compound in the centre electrode.

The performance benefit with Plat, Irid comes from being able to run bigger plug gaps because the reduced firing voltage allows this. Common sense should tell you that the bigger the spark, the better......& more chance of complete combustion.

That big cam you fitted & now idles rough. That rough idle is incomplete combustion & the engine misfiring. I wonder if you had a spark 1/2-1" long.....& hotter....what would it do.
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You can run the same gaps with copper core plugs that you can run with any other plug.

Gap doesn’t make power, regardless of what all the advertisements say. Get a better ignition.
 
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