Ok i know the best thing to do is have it rebalanced!i have a 400 engine and i was wondering if i put a 383 steel crank in it does it need to be rebalanced if i use the 383 flywheel and balancer? Just picking your brains!i'm going to but this in my 68 dart that had a 383 (threw a rod) and the price for the crank kit is the same so my flywheel and everything was for a internally balanced engine!but if the response is to get the cast crank and buy the balanced fly wheel thats probly what i will do!not going for max preformance just a daily driver!

400 pistons are heavier than 383 pistons.

It will vibrate...

Most sources show the forged 400 and the forged 383 cranks as a straight interchange.

We have a 383 crank in the 400 in my sons Dart. We had everything balanced. Ron

With a cheap Harbor Freight digital scale weigh one of the 383 rod/piston/ring/bearing assys' and one of the 400 ring/piston/ring/bearing assys' & post the difference. For the bobweight amt on each journal (4) the reciprocating weight of 1 assy's is used as is plus the rotating weight of 1 assy is doubled then add both sums up but in effect each assy should be the same (or close), for a start post what you get just as if 2 sacks of money contain the same # of pennies and the same # of nickels they will weigh the same. Unless someone has a definitive ans I'd wanna know now (one way or the other) rather than later (& maybe have to start over)

If you put a forged 383 crank in the 400, use the 383 damper and flywheel and rebalance the rotating assembly. Or, I would run the 400 as is with the stock cast crank drilled for a pilot bushing and have the 383 flywheel balanced to the 400 engine.

Have the rotating assembly balanced, trying to find the correct external balance flywheel USED, is going to be next to impossible. the balance job from the factory wasn't that good to begin with , do yourself a favor and have it balanced using the forged crank.

Next dumb observation ... rotating assembly KIT ??? be careful , 400's were low compression from the factory there are very few pistons available that aren't .100 or more in the hole, any would be from companies like ross, diamond, etc ...

Sounds like you are trying to do this on the cheap, you may be disappointed with the outcome.

On the subject of 383 versus 400 internal balance, keep in mind that forged crank 383's all had higher compression height than any 400 so the extra weight that comes from the larger diameter of the 400 piston is offset by the taller compression height of the 383; since the rods and pins are the same, the bobweight would probably be near the same for both (within factory tolerances).

Assuming one would want to stay with the lower compression height piston in the 400 ???

My argument is to why the forged 383 and 400 cranks are an interchange in original form.

If stock (or stock replacement) 400 pistons and rods and stock (or stock replacement) 383 pistons and rods, the cranks will interchange if one keeps the rotating parts together. So cast crank with cast crank damper and TC/flywheel, forged crank with forged crank damper and TC/flywheel.

The engines used exactly the same connecting rods and the stock replacement pistons are the same weight. Mopar engineers were champions at making things work with a minimum of fuss. I bet the early 400 cast cranks and the late 383 cast cranks were the same casting #.

R.

i did this last year because i didnt want to deal with an offset balanced flywheel. i had the steel crank, then my bud hooked me up with a real nice steel flywheel. i decided to spend the money saved on having it rebalanced. it was just a ring job not a rebuild. the machinist told me the bob wieght was very close, and the crank was good on one end but got worse towards the other end. i did talk to guys that did it without balancing, but a shop will have a tighter tolorance than the factory did back then so it could be money well spent.

If it was me, I would buy some KB pistons to get the compression up and take the whole thing to the machine shop for a balance job and get the block bored for the new pistons. It's already apart and the compression you gain will pay off in the performance department.

Hello:
To assume that rods or pistons weigh the same or close is a mistake waiting to happen.
Take any set of rods or pistons to a good machine shop and watch as they are weighed....you will be suprised at how much varience there is. Also rember you have to weigh the total assembly...that is piston-piston rings-wrist pin- connecting rod.-rod cap and bolts- and bearings.
Then match the heavier assemblys to the lightest assembly.
Be sure that is what you want to use to build engine with...any change after balancing like a diffrent set of pistons. will require that you start all over and rebalance.
Some may think that is being picky ---but you spend a lot of money on building a engine...and cutting corners will come back and bite you.

Maynard