fastback wrote:After reading this article:
http://gowesty.com/library_article.php?id=106
Is it critical to keep the moving mass (rods/pistons etc) stock ??
As the lumps on the crank is matched the moving mass?
so bad idea to lighten rod's then??
Yea, I read it. I think the person is full of it.
He says he does not need counterweights because "his pistons" are 5% lighter on stock parts. So what? I can shave 20 grams off pistons. Does that mean I do not have to use counterweights on a motor what will spin 8000 RPM?
But mind you.... he increases the stroke a lousy 6mm and all of a sudden YOU GOTTA USE COUNTERWEIGHTS?
The job of a counterweight is just that...A COUNTERWEIGHT! It is used to offset something. The idea of the counterweight is to offset the weight of the big-end rotating assembly per rod. He has this idea that the "other rod assembly" will offset the other since they are opposed. They have two different forces acting on each opposed pistons. I do NOT think they offset at all.
Only one piston will fire at a time and entirely independent of the other three. There are many dynamic events happening with just that one piston. The added weight opposite the big end assembly will "stabilize" the forces acting on it. And it is dedicated for just that one piston. You are not relying on the other bigend assembly to offset anything.
Also besides being able to dampen the pulses, the added weight can store more energy and keep the rotation moving at a higher rate and more consistently. This is the whole idea of attaching a flywheel at the end of the crankshaft. An engine without its flywheel is a VIOLENT one if you try to run it. See for yourself.
As far as the added mass, things rotate faster if they are lighter. Just fact.
So you cannot have things too heavy either. Lightening the rod is not a bad idea, but it is a LOT of work.
Dynamic balancing is the one very important thing you can do to the engine in addition to competent machine work of the parts.
I have since bought my own balancing equipments to complement the machine shop I already have. Engines run much better when they are fully balanced.