Quote:
Originally Posted by Adger Smith
James,
In the racing world you stay away from the external balance at all cost.
An external balanced crank can be balanced while it is sitting on the engine balancer. It is when you put it in use and the 100+ HP per cylinder power strokes are bending and twisting the crank all different ways the lateral run out of the external weight becomes questionable. There goes the balance!
You also have the "Hit" that the torque converter puts on the flex plate , yes, flex plate is the name of the thing the external weight on the back of the engine is called. Yes, it flexes and there goes the lateral run out of your weight. Your weight conclusions are based on a correct theory, but that is splitting hairs and with a race car it would brobably be a wash with the other balance/flex issues. What happens in the lab under controlled conditions is not what usually happens in the real world. Over the years Racing has shown me just that! Ask any racer that has spent thousands of dollars on the gundrilled, lite weight, exotic weight everything just to gain nothing. I hope this didn't start a firestorm about balancing! Yikes!
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X10!
There are also a lot of dynamics involved that are not constant due to the acceleration rates of a drag racing engine. Bobweight numbers and size also an effect on the inertia and acceleration of the crankshaft.
Like Adger and Art have shared, a crankshaft design may work in one application and may not work in another.
So in a nutshell, go internal balance in a race engine and leave external balancing to low RPM street engines.