I tried looking this up with no real luck. Some people say it needs a external balanced flex plate / fly wheel and others say no. One form I read said the zzz owners manual recommends external balance. Any info would be helpful especially from other zzz zz1 zz2 zz3 owners. thanks

 

If memory serves, that motor takes the same flex plate or flywheel as any other 1-pc rear main seal motor.

It is INTERNALLY balanced, with the rearmost bit of INTERNAL balance weight located on the flywheel rather than on the crank.

 

ZZ3 and ZZ4 are absolutely 86-up L98 / LT1 style flywheel compatible.

I'd assume based on production years the ZZZ is too.

If it's out of the car, look at the flywheel for a weight. 85-down 350 doesn't have one; 86-up does.

If it's in the car, do some decoding:

http://www.nastyz28.com/chevy-engine-code-stampings.php

http://www.nastyz28.com/sbchevy/sblock.php


Ah, this confirms it:
http://www.crateenginedepot.com/pdfs/sb_zzengine.pdf

 

Externally WEIGHTED; not externally BALANCED.

Two completely different situations.
As the others have noted ; anything to suit a 1 pce RMS engine

 

Which is weighted because a 1pc RMS engine is not 100% internally balanced (unlike a 2pc rear main anything but a 400)

 

Yes those motors ARE 100% INTERNALLY balanced.

The rearmost bit of INTERNAL weight is located on the flywheel or flex plate. The fact that it is on an "externally mounted" piece DOES NOT alter the fact that the motor is INTERNALLY balanced.

The terms "internal" and "external" balance DO NOT refer to which side of the split between the crank and the flywheel the weight is on.

 

so my flywheel off my 305 will work?

 

If it bolts to the crankshaft on the ZZ engine ,it is the correct one

 

89, yep.

If you've time talk a bit more about the engine. I had completely forgotten there was a zz1 and 2. You pick it up used?

 

Yea picked it used from a salvage yard in Florida but has some issues going to need a cam since it has some wear on a lope. I am also installing new rod bearings.