RePete

I will be building a 383 vortec motor for my '85. As i was dis-assembling the donor engine, i noticed the large counter weight on the flex plate. I was under the impression that all chevy 350s were internal balance. So.., i went to the internet. This is what i found:

1. all 2pc rms = internal balance
2. all 400ci = external balance
3. all 1pc rms =int/ext balance

I will be buying a new rotating assembly, and it looks like they come balanced all three ways. Right now, the car has a 700R4, but i plan on a manual swap. My choices would be a zf, T56 or a Keisler kit, but leaning toward the zf (it fits).

So, after all that rambling, my question is: If i go int/ext balance, would i need to re-balance a dual mass flywheel? What would be the best balance with an aftermarket flywheel? I'm kinda confused.

Deakins

If it were me I would internally balance the engine and then get a flywheel that was zero balance. This way you are not having to match balance flywheels like the Fidanza if you go that route with the ZF 6 speed. It just makes things way easier in my experience. Just my .02

mtwoolford

Doing a buildup around a dual mass flywheel is like Monty Python's "Search for the Holy Grail"...it either ain't gonna happen, or at some point down the road, you'll wish it never happened.

I can't speak for all aftermarket flywheels. but my Spec flywheel for a 96 LT4 came with a bolt in counter weight, which when removed, (I believe) makes the flywheel neutral balanced. In either case, it should simplify any future balancing issues vis a vis non stock crank / rods/ pistons.

RePete

Thanks for the replys. I was tending towards internal balance also, but my machinist suggested int/ext. Internal seems to make more sense to me. Just wondering what y'all thought. I didn't realize the dual mass was a kiss of death.

WW7

This is how Pete K did my 383 motor he built for me...30,000 miles later it's still smooth and running great....WW

vetteoz

The aftermarket has taken it upon itself to inaccurately call the 1 pce RMS engine Int/ext balance
(because of the weight on the flywheel like a true ext balance 400).

The fact the rear counterweight was RELOCATED because it could not be part of the crank flange as it was on the
2 pce RMS engines does not change the balance arrangement.

vetteoz

Makes no difference.
If he retains the stock 1 pce RMS balance arrangement with the weight on the flywheel ; the so called "Int/ Ext " balance ,
he can use any off the shelf stock or aftermarket 1 pce RMS flywheel like one for a 4th Gen LT1.

WVZR-1

The OP mentions 383 Vortec and then goes on to mention SBC crankshaft variations. It's either a Vortec or it's not and it would have a direct bearing on everything he mentions intending to do. He mentions dual-mass and then all of the balance options etc. It's pretty difficult to comment if he doesn't actually ID what he's really doing.

Is it an LS Vortec or does the OP just believe all 383's are Vortec builds. Maybe he'll clarify his actual build. He also mentions being confused! He then mentions wanting to use the ZF - he says "it fits". An LS/Vortec with a ZF I don't believe is a straight forward simple build. Maybe I'm mistaken?

RePete

The engine being used for the build is a Vortec 5700 from a 97 chevy van. it's essentially the same motor in my 98 suburban. It's a SBC with a 1pc rms.

Also, it's my understanding (maybe i'm wrong here) that any stock flywheel / flexplate is balanced for a factory rotating assembly. so if i change the assembly and use a stock-balanced fly wheel, will it still be balanced?

RePete

It sounds like internal balance will make my life easier down the road. makes sense. thanks for the help.

WVZR-1

The Vortec 5.7 (truck) with the rear mount distributor sometimes slips my mind in "passenger car" conversations. Yes the Vortec is essentially just a Gen I SBC with some later engineering refinements.

The internal/external discussion could go on for pages and I believe the decision should essentially be discussed with the engine builder. I'd say it's strictly a builder and end user discussion.

mtwoolford

I respectfully disagree. This is a source of endless discussion, confusion and misunderstanding. As so many things in life, it all boils down to money versus convenience.

An internally balanced crank allows the use of a neutrally balanced flywheel; which is great since later flywheel swaps won't require match balancing the new to the old flywheel. Save some time and money there. But here's the rub, to save money, you have to spend money. An internally balanced one piece rear seal crank has no balancing counterweights at the flywheel end and that's going to have to be compensated for in some way, which would be by drilling the crank and adding very expensive "heavy metal slugs". If the one piece rear seal crank with an increased throw (3.75 inch or more) can even accept that much heavy metal is an issue unto itself; suffice to say it will be very expensive.

Internally balancing an increased throw two piece rear seal crank would also require heavy metal, but since the crank retains the external counterweights it would be much simpler. But still, take a note from the factory when they started building the original 400 c.i. small blocks, instead of trying to add more counterweight to the crank itself, the factory simply added a glob of metal to the flywheel.

So, more than a engineering issue, it's largely a monetary issue, but as they say, "you's pays yur money and makes yur choice".

vetteoz

Neither would staying with the stock, 1 pce balance arrangement ,
he is going to have available for use without mods ,any off the shelf , '87+ SBC flywheel ( trans related fitment problems excluded )

Also the supply of neutral balance ( or removal able weight ) flywheels to suit the 1 pce crank bolt pattern is limited compare to the stock " weighted " versions

theadmiral94

RePete,

If you go with a ZF, consider the following:

ZF trannys were matched with the dual mass flywheel to reduce the 'marbles in a tin can' noise generated by the natural flucuations in the crank rotation (regardless of balance).

However, before deciding, might want to verify availablity of a dual-mass flywheel, as recent posting suggest might be difficult.

p.s. OEM dual mass flywheels (e.g. 94 LT1) have holes around the perimeter for balance weights which are supose to be moved from the old to new one when replacing the flywheel AS THEY ARE BALANCING THE ENGINE (and obviously the flywheel keyed or match-pined to the exact same position relative to the crank as the old one).

vetteoz

There are known problems associated with neutral balancing a DM flywheel

http://forums.corvetteforum.com/c4-t...ozing-oil.html

The flywheel will only bolt up to the crank flange in one position

RePete

All good info. glad i asked.