magnum vs LA balance

[chrisII]

i have ben told on this site that the 360 magnum and LA have different balance. i find this as odd being that ive ben told by a mopar parts guy that the cranks have the same PN, as do the rods i would expect. so im curious where the different balance comes from? is it in the harmonic balancer?

[Rolling_Thunder]

the harmonic balancer and weighted torque convertor are different between the LA and the Magnum engine...   

[chrisII]

so then, if a guy wanted to install a magnum in place of an LA he could theoreticly use an LA harmonic balancer and not have to re balance the torque converter or flywheel?

[Chryco Psycho]

no that would not work , piston weight may be the reason for th edifference in balance but you need to use a Magnum balancer & flywheel or torque to balance the engine correctly & not do internal damage

[Rocky]

The following information comes from the book How to build Big-Inch Mopar Small Blocks.

Engine                         1971-92 360 LA                         1993-03 Magnum 5.9L

Piston                               584 grams                                 470 grams
Piston Pin                          154.6 grams                              134 grams
Connecting rod small end     239 grams                                 225 grams
Connecting rod big end       519 grams                                 519 grams
Ring Set                            56.6 grams                                40 grams
Rod Bearing                       47.6 grams                                47.6 grams


Reciprocating Weight          1,034.2 grams                           869 grams
Rotating Weight                 566.6 grams                             566.6 grams
Weight per Cylinder            1,600.8 grams                           1,435.6 grams
Total Bob Weight               2,167.4 grams                           2,002.2 grams


The total weight for each cylinder is 165.2 grams lighter in the Magnum engine.  When eight cylinders are added together, this reduces the reciprocating and rotating weight by 1,321.6 grams or about 2.91 lbs.  The reduction in weight allows it to accelerate faster since it is lighter.

[chrisII]

it seems to me to be similar to taking a stock 318 crank and installing it in my 340 with forged (heavy) pistons.with like 3 seasons and several feature wins on that engine in my stock car i dont think there is a problem, however i dont think its worth the chance on a $3000+ crate motor

[Rolling_Thunder]

yeah - in the paperwork for the magnum crate engines (I'm looking at my paperwork right now) it says about 6 times they CANNOT be interchanged....