408 harmonic balancer?

[Valkman]

I'm building a 408 with a 360 block, the rotating assembly will be balanced. Can I just use 318 / 340 balancer?

 

[Gamedog]

Sounds like a question you might want to run past your engine builder, to be honest. 360s were externally balanced from what I've heard and been told, so you'll want to run a harmonic balancer for a 360 unless your builder tells you otherwise.

318s and 340s are internally balanced if I remember correctly.

 

[Valkman]

the 408 crank is internally balanced, where the 360 in not.

 

[72Dart6pack]

I am currently doing the same. So this info will help me also.

 

[rustycowll69]

I am not positive, but I believe the last year (possibly two) of 340 production, they went to a cast crank, and it required a special dampener. I don't know if that means externally balanced, or still internally balanced. So be aware. I am sure someone else will chime in and clarify the situation.

 

[Valkman]

Yes you are correct the 73 340 is a cast crank with a special externally balanced damper, but believe all the all other 340, 273, and non magnum 318 use the same type balancers.

 

[Plymouth 65]

Yes you are correct the 73 340 is a cast crank with a special externally balanced damper, but believe all the all other 340, 273, and non magnum 318 use the same type balancers.

Valkman, I would suggest using a Mopar Performance 340 internally balanced damper. If you're budget allows, a Fluid Damper would be best. Rubber dampers are specifically tuned to the rotating assembly point of resonance. This system resonance varies depending on many factors. The main factors are cylinder pressure and crank stiffness. Most builders have no idea what the crank system resonance frequency is after performance updates. Fluid dampers work over a wider range of frequencies unlike the elastomer type.