the 3922 plugs are a little cooler than the 3923. the 3922 are for nitrous applications. that way the motor dont go boom. i am happy with my 3923 plugs.

 

As mentioned above...

The standard plug for the 3.9L V6, 4.7L V8, 5.2L V8, 5.9L V8, etc. is the 5224. A lot of people have switched to the 3923 which is a little bit shorter than the 5224 plug, and one heat range colder. The Magnum V6/V8 tends to detonate when hot or under heavy load - the reason people started switching to the 3923 wasto give a more controlled burn by preventing early detonation. Cooler plugs do NOT make more power! If you're feeling "more power" from a 3923, it's because your prevous plugswere probablyFUBAR, or your engine was experiencing a lot of detonation issues (you should also look into replacing your cap/rotor, spark plug wires, use higher octane fuel, etc.)

Standard plug length: 5224
One heat range colder: 5223
Two heat ranges colder: 5222

Shorter length: 3924
One heat range colder: 3923
Two heat ranges colder: 3922

 

Whatmiliage are you all changing these at? I have 06 with 18,550 on it. Non-HO. Do these have to be bought online or are they a normal part carries at the auto parts store?

 

The 5224's should be standard fare at most auto shops. I've found the 3923 to be hit or miss, although my local Wally World Superstore started carrying them on a regular basis. I usually end up replacing my plugs every 5k-10k miles, but I that mileage is usually spread out over a year or longer, and I have taken my trucks to the dragstrip/autocross/etc. so they experience some hard driving.