OK, I've read and read and read on the difference between balanced and unbalanced, internal and external, and I think I'm more confused now than when I began. Seriously though, I get the "internal/external" issue with regard to the 1pc. RMS, and I'd rather not get into that.

Here's what I'm looking at with regard to Summit's "compare", although a lot of these specs don't necessarily relate directly to my question. 1989 5.7, 355/.030 over ,hyper pistons, floating pins, NOT forged crank, and either Scat or Eagle brand. Gives me about 18 options. ALL are 1 pc RMS kits. ALL are for internal balance engines. ..however.....under "balance", some kits say YES, some say NO. What does THAT mean? What is that in reference to?

I have a relatively new GM 153 tooth flywheel (1pc. RMS) that I got when I did the t5 swap, and it's got under 2000 miles on it. I plan to use it.

 

OK, all the "YES" options include a flexplate. All the "NO" kits do not. I'm guessing that answers my question, although the language seems a little misleading. Since 1pc. and 2 pc. RMS flex/flys are NOT interchangeable, is even POSSIBLE to get a 1 pc. flex/fly that is not counterweighted ???

Anyhow, to answer my OWN question, and since I DO have a flywheel designed for 1 pc. RMS engines, my guess is I need a kit that is NOT balanced, as it does NOT contain a flexplate in the kit.

Anyone care to confirm my logic?

 

The fact the flexplate is included would make one assume the rotating assembly is balanced , ready to fit ;
whereas the the "non" balanced kit requires balancing when you fit the flywheel / flexplate of your choice

Some aftermarket 1 pce flywheels have a bolt on weight so they can be used with either balance arrangement
http://www.cnc-motorsports.com/flywh...-flywheel.html

Several 1 pce available for when the assembly has been changed to the early balance setup
http://www.summitracing.com/parts/MCL-460350/

 

I'm confused. So what do I need? Obviously my stock flexplate worked, which I still have. Obviously my current flywheel works. What do I need to use either of those? Forget I ever mentioned L31. Lets just assume I'm gonna rebuild my stock L98 with a new rotating assembly.

 

....or let me ask my question another way. Can I buy a balanced 1pc. RMS kit, ditch the flexplate and run my current 1 pc. RMS flywheel?

 

yes.. as long as they didn't cut corners and grind on the included flexplate to balance it.. any decent shop will use a standard balanced flexplate or flywheel when balancing the crank to allow you to use any replacement piece down the road without the need to get it balanced to your particular engine...

but really, i'd get the cheaper unbalanced kits and have a local shop balance it.. they have been known to be out of whack right out of the box despite being "balanced", so you might as well save the money up front and get it done locally.

 

There is 2 diff balances being talked about here.
Your 2 motors are internally balanced. (which means there is no counter weight on the balancer and flexplate, there is a lil weight on your stock flexplate but its for nutral balance) As far as I know, all 305-350 sbc are internally baanced.
A old stock 400 sbc is externally balanced.
The kits your looking at, come either balanced or not balanced.
I would rather have my local machine shop balance my rotating assy. I have heard, from my machine shop and other shops, that the balance job that gets done at the supplier level has some issues.

 

Yeah, after a lot of reading, I think I agree with what you have all said. Internal or external is the type of balance, yes or no is whether or not it has been done. Having a local shop do the balance seems to make sense, as opposed the manufacturer.

 

Well, having a shop "balance" everything is a good idea because parts from diff places may mean diff numbers for all the parts.

Internal and external balance has to do with how the crank is balanced. (the shop should check this)

Balancing the rotating assy has to do with how the pistons and rods are balanced to the crank. (This is what the shop will balance.)

Hope that helps a lil more.