I am in the process of building my 383 LT-1. I am buying my forged eagle rotating assembly this weekend. It will have the 3.75" crank, 6.00" H-beam rods, SRP pistons, file fit piston rings, clevitte 77 main and rod bearings. I can buy the assembly balanced or unbalanced. My local speed shop told me to buy the non balanced kit and have the assembly locally balanced. He said on the LT-1 motor the front and rear of the crank are balanced to a diffrent weight, and that eagle balances their kits for the small block chevy the LT-1 is diffrent. Have any of you ever heard of the the crank being balanced to diffrent weights at diffrent parts? I want to build my motor the right way and I am unsure what kit to buy. Should I get the balanced or un balanced kit?

I'm also at a loss as to what -dish to get on the pistons. I am getting the fully forged kit that way I will be able to safely run nitrous. The car will be daily driven, and at the track once or twice a month. With that in mind what do you recommned for the compression ratio on my motor? To achieve the desired compresson ratio you reccomend what -dish piston do I need? I will be having the block decked and be running the 6.00" rods, and the stock diameter head gasket. I know those factors make a diffrence in the compression.

Thank you for all the help in advance,
Jason

 

What the speed shop is talking about is that eagle prebalenced assemblys are neutraly balenced if you are buying another flywheel no problem just buy a neutral bal flywheel harmonic bal stays the same. I used a mcloud clutch and all I had to do was remove the weight (two small allen head bolts) I have the same rotating with -31cc je pistons. Fotr your pistons just give JE a call and they will tgive a recommendation for your application.

John Carpico

 

Get the unbalanced kit. Let the local shop do it. I have one of the best balancers luckly around and he did mine with the flywheel bolted to the crank. IMO the only way to go.

 

Trouble is that when you change to aftermarket pistons and rods, the crank needs to be balanced again to compensate for the different weight.

If you buy a complete rotating assembly with all the related parts then it should be already balanced. That's the idea of buying a balanced assembly.

If you're buying it a piece at a time then it will need to be balanced.

 

So basically when I order all the parts for the kit if I request they will balance it and then I will not have to have it re-balanced. What about the diffrent balance from the front to the rear of the crank? Do they do this on LT-1's?

 

Is the LT-1 internally or externally balanced?

Engine like the SBC 400 or BBC 454 are externally balanced. To balance them, the front balancer and rear flexplate/flywheel are needed since they carry extra weight required for balancing.

If it's internally balanced then the harmonic balancer and flexplate/flywheel are neutrally balanced and are not needed to balance the rotating assembly.

 

A stock LT1 is like a 400. It is externally balanced at the rear (the flywheel/flexplate). The harmonic damper, at the front, is neutral balanced. If you are buying a new rotating assembly you have two logical choices.

1. Have it neutral balanced. Then, you can use any neutral balance flywheel/flexplate.
2. Have it balanced to work with the standard 350 external balance flywheel/flexplate. These all have the same amount of weight. Ideally, the balancing would be done with your specific flywheel/flexplate. But any standard 350 piece should be pretty much the same.

Rich Krause

 

If you pick up a GM Performance Parts Catalog (GM Dealer) there is a detailed breakdown of how GM balanced different engines and which harmonic balancer flywheel combo you need. As to balancing the assembly together, if a assembly is balanced properly (internal or external) as long as the right flywheel is used OK, its easy to get flywheel balance right.

John Carpico

 

So, if I am swaping from A4 to Manual transmission and used the regular SBC350 flyweel, it has to be balanced. Is that correct?.

What would be the problem if the swapped in flywheel didn't have any weights.

 

I am not trying to hi jack your thread, but I have a question. If the LT1 uses the flywheel and balancer to externally balance it? Why is there no notch on the crank for the hub and balancer? I mean there's nothing that is going to make it go back on the exact same way. If thats the cause how can it be balanced since the position of the balancef isn't going to be consistant. Also, I have heard some of these same things from my local machine shop who I trust, but they don't do very much late model performance builds, mainly LT1's. I had asked them about the balancing a 383 when I was considering doing on myself. Then my machinist starting talking about neutrel balancing, and how it had to be balanced anyway, and that they add mallory to the crank and it would be like a 400 dollar balance job. After that and some other decideing factors I decided to stick with a 355. Which leads me to more questions but I will stop here.
thanks

 

The front is internal and the rear is external on those engines.

 

1FastRedZ----I have one of the best balancers luckly around and he did mine with the flywheel bolted to the crank. IMO the only way to go.


whats the name of the shop your talking about and how much did it cost? thanks man

 

How in the heck did GM do that? I talked to my machinist this morning and he said the same thing about the way it's balanced. He said he has seen some 383 balance jobs were they had to cut the front counter weight almost all the way off.

He also said if I go with the speed pro forged pistons they may have to add weight because the pistons are so heavy, wereas KB silvo lites are lighter and normally remove material.

 

The LT1 and all 1 peice rear seal factory cranks are balanced in the front and not in the rear.

If you look at the older type sbc cranks youll notice the extra material on one side making the flange a rounded rectangle shape. the 1 peice rear seal blocks dont have room for this so they add the weight to the flywheel\flexplate. , but from the rear bearing forward the LT1 crank is practicly identical to the older 350 cranks.

 

The name of the shop is Lynch's Machine Shop. He is just outside of downtown Greenville SC, on HWY 123. It is $150 to balance a rotating assm. including flywheel. The owner is Philip Lynch and his number is 864-269-9090.