Suggestions on which plugs to go with

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Rude72*

Rude72*

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Hello all...

I am going to buy some new plugs for my '72 Duster 340. I am quite the novice here, so I was looking for a little guidance. The specs for my car are listed below. That's about the extent of what I know regarding the car's motor, trans and rear end. Suggestions for plugs? Anyone running a similar setup? Many thanks!

-Correct Vintage 340 block bored .030 over.

-TRW forged pistons & Speed Pro Piston Rings-Compression 11:1

-Mopar Performance Purple Shaft Cam P4120235

-Performance Electronic Ignition with chrome box and Accel Super Coit

-340 heads rebuilt with new Valves, hardened valve seats and 3 angle vale job

-Hooker Comp Headers with Jet Hot coating mated to 2.5" exhaust with cross pipe and Flowmaster Mufflers

-Holley 750 Carb atop Edelbrock Torker I| Intake manifold with K&N Air Filter

-Mechanical Holley Fuel Pump on engine as well as secondary Holley Electric

-Fuel pump located near fuel tank and operated by switch in cabin

-3 row radiator with overflow bottle and Mopar Performance Viscous

-3.23 gears (switching to 3:91 gears soon)

-11:1 compression

-Mopar 727-A automatic transmission

-3200RPM Stahl Speed Trans Specialty Converter

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Rude72* said:
Why's that? Do they foul easily, have poor life? What do you suggest for 11:1 compression?
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I was being facetious. You will find spark plug threads will usually have someone trashing every brand of plug by the end of it.

I like NGK and Champion plugs in my junk. I’ve been running Champion N9YC in my Commando 273 which is 10.5:1 and they were a big improvement over the autolite that came out(same heat range).

Whichever plug you choose, carefully inspect each plug, and verify the gap before you install it.
 
I have run the Champion RN9Yc in my 340s for 45 years. Are they the best. Who knows. It they were the factory plug Chrysler chose to put in them. Yes I have tried others but always went back to Champion. Your results may very. Kim
 
I have found that champ’s always worked better than other brands I tried except for a set of accel plugs I tried. Those worked as good.
Generally the higher the compression, the colder the plug, and I’m sure there is a whole lot more to it than that. Best to stick with one brand and keep trying different heat ranges till you find what works best. I would start out with a stock heat range plug or one range colder. Then again that used to be easy when plugs were stupid cheap in the 70’s.
 
Tell us about "11:1". Is this a measured and KNOWN 11:1" Is this a "my brother's friend's hooker girlfriend said it's 11:1"? If you don't know 100% FIRST HAND then we might need some compression test numbers. ....and it wouldn't hurt anyway. I would say an "HONEST" 11:1 engine would use a plug one, maybe two heat ranges colder than stock.
 
RustyRatRod said:
Tell us about "11:1". Is this a measured and KNOWN 11:1" Is this a "my brother's friend's hooker girlfriend said it's 11:1"? If you don't know 100% FIRST HAND then we might need some compression test numbers. ....and it wouldn't hurt anyway. I would say an "HONEST" 11:1 engine would use a plug one, maybe two heat ranges colder than stock.
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All I know is I had a couple sheets of paper that came with the sale (from the owner) with a long list of mods and specs. I guess I'll just go with a "stock" plug for now and see what happens. Thanks.
 
oldkimmer said:
I have run the Champion RN9Yc in my 340s for 45 years. Are they the best. Who knows. It they were the factory plug Chrysler chose to put in them. Yes I have tried others but always went back to Champion. Your results may very. Kim
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Thanks for the information!
 
Rude72* said:
All I know is I had a couple sheets of paper that came with the sale (from the owner) with a long list of mods and specs. I guess I'll just go with a "stock" plug for now and see what happens. Thanks.
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I don't think that'll hurt a thing. You can always read the plugs from there.
 
NGK BKR6E plugs is all I run in my 340 and 03 magnum ram

IMG_5396.jpeg
 
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I contacted the guy who sold me the car and he said that he always just used the "stock" plugs and never had a problem. But that doesn't necessarily mean that the car was running at its peak performance either.
 
Rude72* said:
I contacted the guy who sold me the car and he said that he always just used the "stock" plugs and never had a problem. But that doesn't necessarily mean that the car was running at its peak performance either.
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But now you have a legitimate starting point.
 
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