Internally v. Externally Balanced 383 ID

[FitzK25]

Bought this rebuilt long block a while ago, cleaning it up and trying to put it together. It was built 20 plus years ago, changed hands several times, and was never installed. Unfortunately I do not know any of the specs. Thought it was a 350, turns out it's a 383 after measuring the stroke. It did not come with a balancer or a flex plate. I'm trying to figure out if it's internally or externally balanced to purchase both. Crank appears to be cast? (unclear, the parting lines have all be ground down). It's a SCAT crank, the only numbers I can find on it appear to be "0501," a timing mark on the rear, and someone wrote "317571" in sharpie on the front. If anyone has any ideas on how to ID the crank and find the right balancer and flex plate, that would be great. Attaching photos.

 

[xm20k]

Forged at the pen, cast is on the right. As far as balance most likely as it was built 20 some years ago it's probably going to need a 400 balancer and flexplate (externally balanced) unless you can spin it around and find a bunch of Mallory in it somewere.

You must be registered for see images attach

 

[bucket]

What does the rear crank flange look like? The internal balanced cranks had a different flange with a smaller bolt pattern.

 

[77Dmax]

What does the rear crank flange look like? The internal balanced cranks had a different flange with a smaller bolt pattern.

This is not accurate, and especially not when dealing with aftermarket cranks. Theres way too many variables here, and 400s were the only pre-86 sbc to be externally balanced, and shared the same flange as any other internal balance sbc. Stroker cranks were made with both one or two piece style flanges, both internal or external balance.

The OP needs to call Scat and see if they can identify what he has

 

[bucket]

This is not accurate, and especially not when dealing with aftermarket cranks. Theres way too many variables here, and 400s were the only pre-86 sbc to be externally balanced, and shared the same flange as any other internal balance sbc. Stroker cranks were made with both one or two piece style flanges, both internal or external balance.

The OP needs to call Scat and see if they can identify what he has

It is sort of accurate, I just worded my statement poorly. If it has the smaller bolt pattern flange, it is meant for use in a 1-piece rear main block which is mostly internally balanced. Yes, there would be a weight on the flexplate, but that's the only standard option for the later cranks and the balancer is neutral balance like the older internally balanced cranks. When the engine is removed, the rear flange (and seal of course) is the easiest identifier.

If it's a 2-peice seal and the larger pattern flange, then yeah, more investigation is needed.

 

[FitzK25]

It is a two-piece seal with a larger pattern flange. I called SCAT today - unfortunately, this crank predates them putting the full model number on them (at least 25 years old), and as such they could not positively ID it. That being said, it is clearly a cast crank, lacks any Mallory weights added in, and has an alignment dowel in the back for a weighted flywheel. The guy I talked to at SCAT agreed it is likely an externally balanced crank considering all that.

 

[Bennyt]

It is a two-piece seal with a larger pattern flange. I called SCAT today - unfortunately, this crank predates them putting the full model number on them (at least 25 years old), and as such they could not positively ID it. That being said, it is clearly a cast crank, lacks any Mallory weights added in, and has an alignment dowel in the back for a weighted flywheel. The guy I talked to at SCAT agreed it is likely an externally balanced crank considering all that.

Glad you got your answer. When I was working at PAW in the 90's, the 383 assembly we produced was extremely popular and it seemed like we were selling/shipping 5 a day of the Scat stroker cranks. Super rare to slow down production to build an internal balanced assembly. Only the most hardcore streetracer or super stock class racer that didnt want anyone to know it wasnt a 350 would request it.

However, In those rare cases...it still wasnt a true internal balance assembly, a 400 flywheel/ flexplate was still used to save on mallory. And 350 dampener used to pass inspection. While im sure it was done, im not aware of anyone using a 350 flexplate/flywheel.

 

[bucket]

It is a two-piece seal with a larger pattern flange. I called SCAT today - unfortunately, this crank predates them putting the full model number on them (at least 25 years old), and as such they could not positively ID it. That being said, it is clearly a cast crank, lacks any Mallory weights added in, and has an alignment dowel in the back for a weighted flywheel. The guy I talked to at SCAT agreed it is likely an externally balanced crank considering all that.

Well, you will know for sure when you put it together and run it, lol.

 

[77Dmax]

If your running an automatic the 400 flexplate is readily available. 400 flywheels are harder to find, but you can always run the sandwich weight.