Quote:
Originally Posted by Tom Vaught
One other comment on my Post #29.
People might ask: Why did the RA-IV SD engine have a different weight pin in the TRW piston vs the normal 250 gram pin used in the typical TRW Forged Pistons or Cast Pistons in normal Pontiac Engines?
Stock Pontiac Engines for 400 cid engines used a given Bob Weight to balance the cast iron 3.75 stroke crankshaft.
The Ram Air IV SD engine used a Kellogg Steel 3.75 stroke Crankshaft.
"Cast iron is no heavier than steel on a pure density basis. Anything made out of cast iron rather than steel is heavier because it needs to be much thicker. ... Cast iron is usually defined by its carbon content (>2% by weight), and steel typically has <2% carbon."
Simple terms the balance of the engine is slightly different with the steel Crankshaft vs the Cast Iron production weight. As said above, for similar strength the Cast Iron crankshaft needs to be heavier. Steel being lighter = a 200 gram piston pin will work vs the normal 250 gram pin. 50 grams is not a lot of weight but it does help with the balancing of the engine parts. I was told that every one of the RA-IV SD engines was balanced.
Tom V.
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We know that engineers do stuff for a reason. So if a 200g (or 192 or 194) pin is strong enough for a RAIV, why did they not use that in everything and balance accordingly? Less metal in the pin, less in the counterweights, if the quantities were equal, it seems like less cost. Or is it that the 200g pin is a more expensive alloy? I think we are getting a little off topic here.