Offset grinding crank ?

[Dave Gantz]

Anyone know the origin or purpose of the .013 rule? (Is it actually .015, .002 to be safe?)
As John implied, the small amount of cubic inches (inch?) gained seems, even though every little bit counts, hardly worth it, unless there's an ulterior motive.

[Mark Yacavone]

Originally Posted by Dave Gantz

Anyone know the origin or purpose of the .013 rule? (Is it actually .015, .002 to be safe?)
As John implied, the small amount of cubic inches (inch?) gained seems, even though every little bit counts, hardly worth it, unless there's an ulterior motive.

Dave, Years ago , some crank strokes turned up short in teardown. NHRA decided there might be an advantage in altering the b/s ratio. They decided the limit would be + or - .015.
Of course come crank companies began to offer "rules rider " cranks at + .013..So it began..
Not a lot there, but you might as well take it. Plus, a smaller crank pin can't hurt, can it?

[Larry Hill]

Some makes get to grind crank pin from 2.437 to 2.200 in stock to "fit" the rod.

[Dave Gantz]

Originally Posted by Mark Yacavone

Dave, Years ago , some crank strokes turned up short in teardown. NHRA decided there might be an advantage in altering the b/s ratio. They decided the limit would be + or - .015.
Of course come crank companies began to offer "rules rider " cranks at + .013..So it began..
Not a lot there, but you might as well take it. Plus, a smaller crank pin can't hurt, can it?

Thanks Mark. Still trying to learn something new every day.
IIRC, it was the early 90's? At the time, I remember my partner and I wondering what was up with it. When we ran a car in the mid 90's, if definitely wasn't fast enough to warrant being looked at. lol It was a 440, maybe we were bogus and didn't know it. I know we never checked the stroke. Figured a stock crank was just that.