I want to buy an ATI harmonic balancer for my 455 build but Ive got some questions:

Aluminum or steel?
6" or 7"?
internally balanced or externally balanced? Explain the difference?
Does anyone recommend another brand?

This engine will produce 450-475hp. Any tips or info will be greatly appreciated!

 

Steel, 6 5/8 or whatever it is, external. You don't want to pay for an internal balance for a 450hp street motor.

Jmo.

 

Internal and External balance refer to how the crankshaft is balanced. External balance uses weights on the balancer and the flexplate/flywheel, which means the crank by itself (with the rods/pistons) is *not* balanced. Internal balance means weights are not used on the balancer or flexplate/flywheel.
Internal can net some subtle performance improvements and reduces crank harmonics because you don't have those weights flinging around on the ends. So it's a better design, but harder to make fit inside an engine.
Most (all? certainly all I've ever heard of) Olds are external balance from the factory. Converting is very expensive and IMO only worthwhile for serious racing. The harmonics can break cranks at high RPMs.

If you're doing a rebuild, have the rotating assembly balanced with your new balancer and whatever flexplate/flywheel you'll use. Replacement balancers frequently have a different weight than stock.

 

Thanks guys! I'm gathering parts and will hand them over to the builder. Just wanted to know what I should buy.

 

There are SFI approved balancers that won't fail and are required for racing if your car runs in the 10s or better. Others can be anything regarding quality, and some are chinesium. ATI is good; I have a Pro Race.