Shorty plug part numbers for 73 340 & detonation.

[73Challengr]

Hi all, anyone got shorty sparkplug numbers for a 73 340?

Also (sorry, I know spark plug conversations are a pain) i'm running headers. When I changed plugs last time the 2 that are "boxed in" by the header (driver side rear) were very dirty. I do have slight detonation under power even with high octane + octane boost, I'm guessing its one or both of the driver side rear cylinders based on the dirty plugs. The other plugs looked good.

Any thoughts on running 2 colder plugs in the driver side rear and "normal" plugs on the rest? Help, hurt...absolutely no difference?

Thanks much.

 

[Chryco Psycho]

The shortest spark plugs I have found is Accel & they are not a lot shorter . Sorry I don't have a part#
No harm in trying a cooler plug but if they are fouling now cooler plugs will foul faster .
Poorer quality headers can make 5&7 cyl a pain to access .
Detonation can be a lot of things , timing , fuel mixture , plugs carbo build up in the cylinders , tuning the carb may get rid of it without changing timing .

 

[KVB]

The shortest spark plugs I have found is Accel & they are not a lot shorter . Sorry I don't have a part#
No harm in trying a cooler plug but if they are fouling now cooler plugs will foul faster .
Poorer quality headers can make 5&7 cyl a pain to access .
Detonation can be a lot of things , timing , fuel mixture , plugs carbo build up in the cylinders , tuning the carb may get rid of it without changing timing .

I pulled out some really fouled RN12YC (340 w/J heads) and replaced with NGK BPR5ES (which is a little cooler?). To my eye, they were a thread or so shorter and I didn't break them installing under hooker comps....

I noticed a difference just changing plugs and plan on upgrading the wires and distro cap, just to sure everything up.

 

[Chryco Psycho]

Cool at least you are getting it running better !
The NGK plugs I have found to be very finicky & if they start to foul they will fail fast .

 

[AUSTA]

Same found once NGK have failed they will not clear where the Champions will fire & burn off the carbon once the system leans out