External Balanced 360 With new parts still Balanced??

72DMag said
@Marcohotrod you are right. I'm sorry I was thinking big block there for a second.

@nm9stheham Doing more research and referencing the build in hotrod magazine done by IMM. They used the following icon piston and had no issues and no rebalance but it is much heavier then stock. with external balance how much difference compared to stock bob weight can you get away with?? Looks like the icon piston they used was 38 gram heavier than stock. That seems like a drastic difference to me!
Stock: 474 +136 =610 grams Piston/pin actual weight.
ICON IC741: 530 + 118 = 648 grams from Icon website.
KB107: 524 + 132 = 656 grams From KB website.

https://www.hotrod.com/articles/build-500hp-capable-360-magnum-short-block-cheap/

Good observations.... and this got discussed before. (I think I asked Brian of IMM here...) The ring pack is lighter for the ICON's to make up some of that weight difference.... at least that is what I recall off the top of my head was the answer. Ditto for the KB ring pack. My own observations: You can pull 5-8 grams out of the pistons without too much effort, some off of the rod small ends, and there are lighter pins available. The UEMP pin locks add 2 grams back in, but are not used for press fitting.

No one really seems to 100% knows the factory tolerance, but a +/- tolerance of 20 to 30 grams has been cited here, based on measurements and balance work done through the years.

The numbers you list for stock Magnum pistons is very close to my data.