I did a little CAD work this afternoon with what we know about the new crank. Pretty interesting stuff. A .200 increase in diameter (without any decrease in rod journal width) increases the cross section between the second main journal and the first rod journal by almost 7%.
A 7% increase in cross section is exactly what we ended up with when we reduced the rod journal width on our billet cranks at the beginning of this year.
Code name NR for narrow rod journal. Fundamentally we machine the excess width off the big end of the rod (.125) that is already wider than the stock rod bearing. The cranks are manufactured with rod journals that are .250 narrower than stock Dmax. The result is crankshaft counterweights that are .125 wider. This means much less weight has to be added to the damper and flywheel for balancing. In effect moving more towards an internally balanced crankshaft.
The only two drawbacks I see to the 2017 crank is an increase in bearing surface speed with the larger diameter. Which is not really a huge issue at our crank speeds. We rarely see problems with rod bearings. The second is weight. All things being equal, increasing the rod journal diameter has added weight to that side of the crank, (similar to adding weight to the big end of the rod) which means it needs to be counter-weighted for balance in some fashion. If GM wasn't able to add mass to the counterweights, they had to add it to the damper and flywheel.
I can't wait to get my hands on the new cam and cylinder heads to see what changes GM made there. :hug:
