In asking about between a magnum and an LA 360.
Is the pistons or the rods or the crank? And can any of those be interchanged?
I have "some of both" LA/Magnum that id like to put together into 1 unit if I can
My son has all 3 from a LA, I have all 3 from a magnum.
Main question is my magnum needs bored, his LA pistons are still on LA rods (could be swapped out to magnum rods) and are the 30-over I'm needing. How much of a cluster**** of a balance job would it be to be able to build an engine with what I have?
Along that line what would it take to balance it neutral like the 318?
Why did they do external balance on the 360 in the first dam place?

I do not know the answer to your questions on what internal parts if any will swap between the LA and Magnum.

But while waiting for someone who might know for certain, you could look at www.magnumswap.com for information. They have a lot of good info there and I use it from time to time myself.

I'd bet it could be balanced internally like people do with the stroker cranks that are used to make 408s with. On those builds it takes drilling holes in the counterweights and adding tungsten slugs. Not exactly a budget build task. The oem counterweight on the flexplate would need to be removed also.

No matter what combo you come up with the balance should be checked and updated. I don't think a normal balancing job is all that much money unless you get into making drastic weight changes to the assembly that require more effort to solve.

The 5.9 Magnum pistons and Magnum rods are both lighter than the 360 LA piston and rod.

The 1995 Ram FSM has the numbers but the correct Magnum 5.9 V8 piston weight numbers and piston drawing are in the V10 engine section of the 1995 FSM.

The weight and drawing of a piston in the Magnum 5.9 V8 section of the 1995 FSM are incorrectly the old 1992 TBI 360 V8.
I do not think this is corrected even in the 1998 Ram FSM, maybe not in the 2001 FSM.

I think from 1995 to 1996 the rear external balance weights went from on the 46RH torque converter to a weighted timing slotted flex plate.

I have the book “How to build High Performance Chrysler Engines” by Frank Adkins but it does not have the tables of different weights and lengths.

The Book “How to build big inch Mopar Small Block Engines” by Jim Szilagyi might have the tables.

https://www.ebay.com/itm/1159026657...msclkid=e77323b2243f10e5796446ff7acf4e7f

A machine shop that routinely does engine balancing could do a custom mix job since the 360/5.9 is externally balanced.

Szilagyi book says
Magnum 5.9 V8
piston 470 grams
Piston pin 134 g
rings 40 g
rod 225 g small end
rod 519 g big end
rod total 744
rod length 6.123 jnches
width .9305 inches

1971-1992 LA
piston 584 g
pin 154.6 g
rings 56.6 g
rod 239 g small end
rod 519 g big end
rod total 758 g
rod length 6.123 inches
width 1.200 inches

2000-2001 Viper rods ( P5007504) are made from the Magnum forging but are 6.221 inches long and come stock with ARP rod bolts.
Viper rod piston pins are 0.039 inches smaller.

The difference in rod weight looks negligible. Looks like mostly the pistons. I wonder if there's enough meat in the LA pistons to eat away 100g?
Cuz the LA 360 pistons are the main parts I want to use on the magnum "because I have them". They're speed pro hyper, coated, flat top, (besides valve reliefs)

Szilagyi writes up more than 6 Mopar SB engine combo’s including several that mix LA and Magnum parts.

Szilagyi writes in several of these combos that engine balancing must be done but “almost never” is expensive “mallory metal slugs” required.

Find a shop that has done this before and get a up to date $ quote.
Inflation has got our attention and the $ estimation Szilagyi gives in 2005 for each combo seems “real low” to me.

For example he lists $150 for crank balancing on a
Speed O Motive 390 cubic inch V8 with year 2005 “approximate total engine kit price” of $1550

100grams is 1/5 of the piston. I had to take 20 out a rb stroker piston one time, it is an ungodly amount.

Here is the difference between a LA 360 and a 380 hp Magnum 360, 380 is .020 over. La is heavier

Wow. Not by as much as I was led to believe. The LA pistons might just work fine I. A magnum with magnum crank, rods, balancer and weighted flex plate. 30g is only about 1 oz.

So I wonder what a "balance job" would cost as opposed to leaving the LA pistons collect dust, vs buying a set of 30-over flat tops "for" a 360 magnum?

Here I want to say a basic balance job on a normal street type rotating assembly is $150 ish from having it done years ago.

Should you be multiplying 30 grams by 8 cylinders?

I have not balanced gasoline engines,
but I have balanced the rotors of big 100 to 600 hp electrical motors
and even 30 grams of imbalance will cause the assembled motor to “walk across the floor” due to vibration as it runs just below 1800 RPM with no load.
I would guess the vibration at 4000 to 5000 rpm to be very noticeable.

I just had the machine work done on my 5.9 Magnum. I ask my machinist what it would cost to rebalance the motor to be internally balanced. He said it could be 600-800.00 depending on how much mallory he has to use.

Sometimes they do external balance because of the crankcase size limits, sometimes to save on changing crank counterweight dimensions, sometimes because the needed counterweight mass just won't work. You do not grind, drill, or otherwise sodomize the parts except to bring each into balance with the lightest of the parts, in other words make al the pistons the same, rods ends the same etc. This isn't much needed on modern decent parts, any benefit of reducing the sub-gram difference between pistons etc is outweighed by adding stress risers or otherwise mucking up an engineered surface. Old school OEM parts often had pads specifically for balance grinding, ie rods.

That 30gm difference is significant, could be more or less depending on if the mass difference is in the reciprocating or rotating parts. S/F....Ken M

It could also be more or less between the two, I didn’t weigh them all just picked up two from the box. Plus like you said, there could be a big difference between the big and small ends between rods. The magnum rod was a tad smaller in the neck up at the piston. Pin different too