i'm guilding a sbc 400

wondering if its imparative to balance the engine internals?

the crank is a scat 9000
forged scat i beam rods
forged flat top srp pistons

also what does it mean when they say internally balanced and externally?

I've always been lead to believe that they wouuld add weight or take weight away from the flywheel or balancer if externally balanced,

and if internally balanced, from the crank shaft etc

cheers

blake

 

A rotating assembly with a new crank should be balanced.

Internally balanced means all the weight necessary to balance the rotating assembly is located on the counterweights inside the engine, and the flywheel and damper are neutrally balanced.

Externally balanced means that some of the balancing weight is located outside the engine on the flywheel and damper. The flywheel and balancer themselves don't have to be altered from their stock specs.

 

I was told that the old 400 cranks weren't balanced so they did it by special dampers. But if you buy a internal balanced crank then you can go with internal balanced parts. I would still have all the parts balanced together before you build the engine.

 

When GM made the 400, they weren't comfortable putting a 5.7" rod in it, because this would have raised the wrist pin too high, so they used a 5.454" rod instead. Shortening the rod meant there wasn't enough clearance to put large enough counterweights in to balance it internally, so they put the weight on the damper and flywheel.

A 400 can be internally balanced though, by using a longer rod with an aftermarket crank and pistons, or by adding heavy and expensive Mallory metal to the counterweights.

 

I am putting together a 434. I've had the mains spayed and went with the Eagle esp "H" beam rods and crank. This should really stroke!

 

have your mains spayed or neutured this is bob barker saying soo long

 

Racing engines should never have their mains spayed as it tends to reduce their aggressive tendancies and makes them prone to sitting in the driveway getting fat and lazy.