Which spark plugs to use

[blown motor]

I have a 340 with 10.1 compression. Currently have Bosch Super RO 362 plugs. They've been in for 12 years so I think it's time to replace them. Is there a better option?

[chargerdon]

On motor trend on demand, they have a section called enginemasters..  On that show on season 8 episode 8 they dyno test an engine with multiple different spark plugs.   The results are interesting. 

First, the difference in horsepower between the best results to worst was only 3 hp on a 600+ horsepower engine.   Second, setting an Autolite plug between .020 gap to .065 gap also increased horsepower by the same 3 hp.   

Lastly, the inexpensive Autolite plugs were among the best !! 

Of course they werent testing for durability but agreed that the Platinum plugs will definitely last longer and they werent impressed with multi strap designs.  Very interesting.   

[Bullitt-]

 From what I'm seeing higher compression engines benefit from copper & we all know what CP likes

Deals aplenty if you get enough to offset shipping 
https://www.rockauto.com/en/catalog/dodge,1970,challenger,5.6l+340cid+v8,1078433,ignition,spark+plug,7212

[cudaragtop]

I'd say 12 years on the same set of plugs is good enough reason to stay with them. my 2¢ fwiw

I've been running Champion RC12YC in my 418 C.I. stroked 340 with 10.5:1 for 11 years since being rebuilt, but not the same set of 8 for all 11 years...
Fouled more than a couple sets before getting the tune right but they've been good ever since.
Not sure how long the current set has been in there.

[benguin]

Interesting that Rock Auto doesn't list the NGK 4006 (formerly BPR5ES) for the Challenger 340, but does for the 'cuda 340. 

I've used the NGK copper/nickel since I saw that Paul Rossi used them in his 440-6 Challenger.  Mine still won't do wheelstands like that car did though (unless there is a jack under the front end, and even then, not as high as that thing would launch).

Seriously, they've been good plugs for me at a price I don't feel guilty about guessing about replacement time.
  Ben

[dodj]

From what I'm seeing higher compression engines benefit from copper & we all know what CP likes

I think NGK gets him racing...right?

[dodj]

I have a 340 with 10.1 compression. Currently have Bosch Super RO 362 plugs. They've been in for 12 years so I think it's time to replace them. Is there a better option?

I'm a champion guy, had good luck with them and easy to find locally. I've never bought bosch plugs...But...with the pics you showed in the other thread I'd stay with what you have. Can't complain about their service life. The guy that owned the car before you might have already gone through a few brands and found those bosch plugs to be the best for that build.

[blown motor]

@dodj Those were put in when the engine was rebuilt 12 years ago. I don't know what was in it when I bought it.

[dodj]

@dodj Those were put in when the engine was rebuilt 12 years ago. I don't know what was in it when I bought it.

Ah..ok....but I'd still stay with them...they look good.
How long you own the car Murray? I picked mine up in 1985....sheesh..been a long time.

[blown motor]

Bought it 12.