what are good spark plugs to run on a 340 and gapping ?

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1nasty_dart

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Hey everyone you guys have been a big help with helping me finish this restoration on a 68 dart gt that someone else started and I needed to finish .the car started out as a 273 and now has a 340 out of a 71 dart the last owner told me . when I got the car the electronic choke wasn't hooked up so you would have to pour gas down it . I hooked it up and my buddy changed the jets to 76 front and 88 back and 13.6:1 air to fuel since the guy had it running rich before( that's what the guy told me and I believe he had 76 jets in rear also ) . The car was running really nice all day Saturday and part of Sunday morning. It was low on gas so I put 15 in and drove home fine which was around the block and then I moved it 2 more times . then out of no where started running rough n felt like it had no power and wanted to stall.. I put the same gas in right after in my 71 mach 1 which is still running fine so I don't think it was the gas. I know the guy I bought it from said the plugs haven't been changed in 12 yrs so I figured I would new plugs and see if that helps since i 'm trying to sell the car . what is a good plug people are running with part number and gapping size? I just wanna run to auto zone and make sure they give me the right ones . the motor is a 340 with I think a small cam , headers ,msd blaster coil and i believe a holly 4150 single pump. thank you !
 
The 3.3L-3.8L minivan spark plug from 96 - 2000 will fit the hole and is a titanium 100,000 mile plug.
 
I would check if autozone has champion n10y, and inspect some of the old plugs and maybe go hotter. gap at stock .035"
 
Whatever regular Champion plug the book says for it.
 
NGK, seem to work the best in my car. Gap at .035 for points, if you have a good electronic system I would shoot for .040, on my MSD setup I go .046.
 
71 340 from the factory would have had Champions N9YC.
 
Always a closet Ford fan hanging around.....

Can't stand Autolites in my MoPar.
Now when my wife has her '68 Stang, that was THEY plug to use!
 
oldkimmer said:
............So the op is just supposed to pull a plug number outta thin air I presume?........kim......
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Which is exactly why I gave the answer I did. Usually, 99 times outta 100 whatever the factory plug is will either be dead on or get you real close. After that, brand is personal preference.

I simply assume since the OP has sense enough to post on a forum, he can look up a plug application. That way, he can make his own decision based on his own preference to brand, rather than listen to a bunch of total BS on a forum where most don't know what the hell they're talkin about.

After all, a spark plug is pretty much a spark plug. People think there's a magic plug out there that will unlock 50 HP. I got news. It ain't happenin. Most anything besides a standard single electrode plug is a gimmick to get your money. Above and beyond that, "I" would not recommend a fancy platinum or the like for any older engine like these. Just not necessary......unless you just feel like wastin money.

Anyone saying one plug "sucks" over another obviously has limited experience, or is simply spouting out of their back side. There's probably only about 3 or 4 plug factories in the world that actually make the plug, so that means chances are the plug you thing is good might be the same plug you think sucks.
 
Anyone saying one plug "sucks" over another obviously has limited experience, or is simply spouting out of their back side.
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Far from it..been playing with Mopars a longggg time Champions tend to foul a LOT sooner then Autolites,get out to the track some time you'll find most racers using them..including most nhra teams:D:D
 
Thanks guys! I went with autollite 65 since auto zone only had those in stock lol. The old plugs we're black but I think the electric choke keeps unhooking which caused it to run like crap. Know I just need to figure out where to adjust it to I did it quick before I went to work and seemed to run better. I ll test it when I get home tn
 
The correct answer is: Champion RC12YC.

If you foul out the Champion "too quick" it is because Champion sets the industry standard for heat ranges and the rest try their best to duplicate it as close as they can, using their own idea of what a correct heat range SHOULD be.

In other words...DON'T USE ANY HEAT RANGE COMPARISON CHART EVER.


If you want to run NGK, ND, AC etc or whatever...look up YOUR application in that spark plug manufacturers catalog.


End of rant............for now.
 
madscientist said:
The correct answer is: Champion RC12YC.

If you foul out the Champion "too quick" it is because Champion sets the industry standard for heat ranges and the rest try their best to duplicate it as close as they can, using their own idea of what a correct heat range SHOULD be.

In other words...DON'T USE ANY HEAT RANGE COMPARISON CHART EVER.


If you want to run NGK, ND, AC etc or whatever...look up YOUR application in that spark plug manufacturers catalog.


End of rant............for now.
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Why would anybody around here wanna do somethin stupid like that? Sounds too much like common sense.
 
About the gap... Is that a function of the ignition system? I know stock is 0.035, but when my car was put together, the guy said he had to gap the plugs (I assume stock type) at 0.055 to eliminate some hesitation or something. It's got the REV N NATOR box and a high performance coil in it.
 
Champion is what mother Mopar used and that is what I have used in my 30+ Mopars over the years with out a single issue.Gap is .35
 
Nuke, the increased gap is for increased ignition power. More power, more gap.
 
NukeBass said:
About the gap... Is that a function of the ignition system? I know stock is 0.035, but when my car was put together, the guy said he had to gap the plugs (I assume stock type) at 0.055 to eliminate some hesitation or something. It's got the REV N NATOR box and a high performance coil in it.
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.055 thats a lot i run a full msd system and plugs are gapped at .045..
 
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