The 383 stroker kit that I am putting in my car is internally balanced. I know that I need an internal balance harmonic damper but I am confused on the balance needed for the flywheel. It is a 1 piece rms, that I know, but I hear that for 1 piece rear main seal motors you can put on either an internal or external balance flywheel. Is that true?

Oh boy, here we go again. . .

An internally balanced 1-piece rear main seal flexplate will have a weight on it. This takes the place of the counter weight that used to be part of the crankshaft of internally balanced 2-piece rear main seal blocks/cranks that was external to the rear main seal.

The factory 400 small blocks and 454 big block engines needed additional external weight that was part of the harmonic damper and flexplate or flywheel because of the longer strokes of those engines. The typical 2-piece rear main seal 383 crank uses those same external balance enhancing parts, the weighted harmonic damper and weighted flexplate or flywheel.

The aftermarket has responded to the demand for 383 stroker small block engines using the later 1-piece rear main seal blocks with 3.75" stroke 1-piece rear main seal cranks. In general, if such a crank is cast, it will be external balance, meaning it needs a weighted harmonic damper and flexplate or flywheel like the factory 400's used; and if such a crank is forged, it will use a neutrally balanced harmonic damper and a "normal" 1-piece rear main seal type flexplate or flywheel like the '86-up 305's and 350's used.

So, long story short - if your stroker crank is supposed to use a neutrally balanced harmonic damper, then you will also use a "normal" 1-piece rear main seal type flexplate or flywheel such as was used by the factory for '86-up 305's and 350's.

The crank is a forged internally balanced set-up. So then it will have to be an internal balance flywheel and balancer right?

Correct, the same parts that would be used for an '86-up 305 or 350.

Ok, well im still looking for a flywheel for my application and I can't find one. All the flywheels for the 86-up 1 piece rear main seal motors are externally balanced. How do I go about getting an internally balanced one then?

I have a feeling you missed this, or didnt understand it.

As noted above ; IF you have factory style internal balance 1 pce seal crank then flywheel to suit will have weight on it

I didn't know five7kid said that but he was talking about a flexplate, does it also apply to a flywheel? And the reason I think that I need an internal balance flywheel is because I bought an Eagle stroker kit and it is an internally balanced assembly. Am I right or wrong by saying I need an internal balance flywheel? Correct me if im wrong.

GM doesnt make differently balanced engines for stick vs auto.
If your stroker kit is internal balance then buy a flywheel for an 86 up. Internal balance is what all the 86 up motors are.

Sorry for the flexplate vs. flywheel confusion.

As stated, the engine won't change because it has a manual vs. automatic transmission.

Think of it a different way: "Neutral" vs. "weighted" balance. A one-piece rear main seal, internally balanced engine would require a "weighted" flywheel or flexplate vs. a "neutrally balanced" flywheel or flexplate.

In your case, you'd need a "regular" '87-'92 f-body flywheel.

So it doesn't matter if I buy an external balance flywheel then, because all the 86 up flywheels that I see are listed as being for external engine balance? And yes, my stroker kit is an internally balance set up.

I sure wish they wouldn't call them "external" balance just because they aren't neutrally balanced, because they aren't "external" balance any more than factory 2-piece rear main seal non-400 flex plates and flywheels are.

The bottom-line question is, "What type of harmonic damper is used with this flywheel?" A "normal" '86-up f-body flywheel will be paired a neutrally-balanced damper.

I bought a fluidampr balancer for the build. It says it is for an internal engine balance with a neitral balance style. http://www.summitracing.com/parts/FLU-620101/

So even though it says external balance I can still use it without any problems then? This is the flywheel that I currently have matched to the current 305 motor in the car. If I could use this flywheel on the new 383 build that would be great.
http://www.summitracing.com/parts/NAL-14088650/

Forget the confusing nomenclature by minimum wage data entry people. Go to the other tab that says:

In other words, that is the 'stock' flywheel.

OK, so I can reuse my flywheel then without any problems correct? I was just always confused when they listed them as external balance, when I have an internal balance motor.

What Max said.

It's a crying shame they call them that.

Yes, your stock flywheel will work (as long as it can take the RPMs and power you'll be putting out).

So wait, "internal" balance isn't actually internal? What's the difference between "internal" balance and "external" balance?

Look at it this way:

"External" balance=400 SBC
"Internal" balance=Everything else

The 383 and the like bring issues into play, whether the 400 crank was used or something with similar weighting. If someone bought an aftermarket crank and its an "internal" balance crank, the intention is that whatever flywheel or flexplate was used on the engine in question (read:not a 400) will still work.

The 86-up flywheels and flexplates are not neutral/zero balance. They have an imbalance and on a flexplate this is easily visible by looking at the weight attached to it. For some reason, the aftermarket likes to call this external balance. This just confuses things with the way people have always described the balancing of a SBC motor. The only time external should be used to describe the part is if its being attached to a 400 crank or a crank balanced like a 400 crank, that uses an additional weight up front on the stock damper. That would result in a lot less confusion.

Like I said, "Oh boy, here we go again. . ."

How many times do we have to explain this?

Thanks for clearing that up.

Yah well it's confusing as ...... So i got a 1 piece seal rebuilt 350. I bought a nonweighted flexplate, because I clicked the internal balanced option on the website search choices. Now I am unsure if I can use this flexplate or need too buy a weighted flexplate.

All I've gotten from this disscusion is external/internal not weighted/non-weighted
Emailed manufacture and waiting for a response

Im building a 383 stroker 2 peace rear main what sould i get Internal or External Balance

Going to add to this thread.When using a 2 pc seal crank in a 1 pc block with a adapter,you have to use the external balance f/plate and the internal H/b.That comes direct from Howards Crank.