Originally Posted by ap72
FWIW, I have swapped pistons to something MUCH heavier and ran the engine without balancing. And many others run race engines that way too. I'm not saying balancing isn't a good thing to do, but I've ran engines just fine without it.
The other issue is that when balancing there is actually only a very small window in which any balance job is perfectly dynamically balanced. Something I wonder about when you see race engines going to anywhere 48-55% balance when 50% is believed by many to be the absolute perfect number for a V8.
Engines like cup enignes that spin over 8000 RPM alot of those cranks are over balanced. The blower engines I build I over balance be 2% as they spin 9500 and no problems.
Machined a block for a customer and the pistons were appox. 72 grams lighter and they said it would be fine. Now that they have runn the engine they are going to take back apart and balance the rotator like I said needed to be done.