Engine balancing question and crankcase pressure issue...

If an LT1 engine is balanced using a brand new weight flexplate and a stock crank pulley, would it put the engine out of balance to switch to Super Damper? They are both neutral balanced, however the Super Damper may weigh more or less than the factory unit and I'm not sure about the diameter (although I think the diameter is the same)

My balance issue is driving me crazy. I have a buddy of mine digging up the stock pulley we used when the engine was balanced.

Also, from 6k-7krpm under load, tons of oil will blow out the rear main seal. Is there a better way to vent that pressure? It's not blowing out the vent tube on the valve cover so I didn't think it would be enough pressure to blow through the brand new seal. Could an imbalance cause the oil to blow out the seal?

Thanks in advance!

Sounds like the engine is internally balanced to me. We had a similar issue when we rebuilt our LT. Stock LT1's are neutral balance on the front and externally balanced with the flexplate on the rear. We installed a new SFI flexplate (non weighted) when we put the trans back in and had an awful vibration upon startup. We then realized after comparing the 2 plates that the stock one was weighted. Put the weighted one back on and voila! If the engine builder said he balanced it im assuming its internally balanced now? Have you tried a non weighted flex plate? As for the oil I guess if its out of balance enough it could be chewing that seal up and letting oil by? not really sure on that one.

The engine was balanced with a stock crank pulley and a weight flex plate. So it was balanced in the correct manner. When we assembled the engine, I wasn't even thinking about it and installed a neutral balanced ATI Super Damper.

My thinking is that the weight of the Super Damper may throw the balance off.

You still running stock crank? If your problem started only after the ATI balancer install I guess the weight of that must be affecting it.

Forged Eagle crank. I never ran this engine with anything but the ATI Super Damper. It was balanced at the machine shop with a stock pulley and installed with a super damper that I purchased later.

You need to you the parts that It was balanced with. If you change anything it will be out of balance.

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That's what I was thinking. At the time, I thought the fact that both pulleys were the same diameter and both neutral balanced that it wouldn't matter. I guess I will get this thing installed and see what happens.

Any special way the stock pulley needs to be installed?