Does anybody know how to tell the difference? I have a Fluidampr off a 383, but I don't know if the engine was internally or externally balanced. There are no part numbers visible that would help either.

Thanks,

Rob

 

not sure about fluid dampner but most/all internal balance parts would look symetrical

 

ALL 383s are externaly balanced, some use a balanced damper like the 400 , some use only the balanced flexplat. all 1986+ smallblocks are externaly balanced also, on account of the one piece rear main that has no overhang to attach to the flex plate, its almost flush. many will argue that, but take a look at your flexplate and you will see a wieght..

 

all 383s are not externally balanced. any rotating assembly could be balanced as the builder wished. just a matter of what you want to do and pay for

 

it is possible to balance a 3.76 stroke crank from a 400 using mallory metal or other heavy metal, but is somewhat rare. the chances of haveing an aftermarket 3.75 stroke internaly balanced crank is pretty good , sorry for the slip up!cosidering that the rotating assembly would have to be re-balanced , it is possible.

 

Okay, here is some more information. The block was an 86+ block with one piece rear main, the crank was an aftermarket Scat crank. So this means that the engine was probably internally balanced and that I have a regular SBC dampner, right? Thanks for the help.

 

prob externally balanced, but you can use an internaly balanced damper.

 

Wow, I sure am glad I already know what I'm doing; I'd be in deep trouble if I was relying on this quality of advice.

It is NOT TRUE that all 383s are externally balanced. That can only be said about ones that were created with stock 400 cranks, and stock 400 rods (5.565"). If longer rods are used, internally balancing the crank becomes a possibility; since then there's room for enough counterweight between the centerline of the crank and the bottom of the piston.

MOST, but not ALL, of the cheeeep offshore aftermarket 383-specific street cranks like Scat, are intended for use with 5.7" rods (stock length for SBC except 400). It is possible to internally balance MOST rotating assemblies with that length of rod.

A crank intended for use with longer rods, such as 5.85" or 6", would almost certainly be internally balanced.

You can look at the crank, and tell a good bit about the counterweights. If it's an internal balance setup, the counterweights should be circular. If it's intended for short rods and external balance, the center portion of each counterweight will be "flat cut", so that the back side of the piston doesn't hit it at BDC. If you're familiar with 400s, you can spot their cranks from a couple of hundred yards away, based on that feature.

The only way to know for sure, though, is to look up what parts were used in your motor; and/or talk to whoever assembled and balanced it.