Jeep Strokers

Lets try something that we can hold in our hands and derive a better understanding of.

Physics and their wonderful world of formulas within can tell us in real numbers the difference in inertia between a 4cwt and a 12 cwt crankshaft.

Lets forget torsional stiffness, harmonics and other crankshaft nuances and concentrate on just the one aspect of rotational inertia.

The amount of energy needed to speed up and slow down the two different crankshafts.

According to the JS FAQ`s a 4 cwt weighs 46 pounds and the 12 cwt 66 pounds. So lets go with that as factual information. The diameter of the cranks are the same AFAIK but I can measure one of my 12`s and I am sure Russ or somebody can measure a 4 cwt if so desired.

Since I am old, feeble and have burned too many brain cells I am going to ask that one of you physics nerds to Google an inertia formula (there are plenty) so we can see what your working with and do the math.

Lets not complicate things with flywheel weights or lack thereof but just the crank itself.

I don't care that Billy Bob`s Cherokee spins up faster then Joe Blow`s Wrangler. I want to see the numbers in simple terms that a layman can understand.

Any takers ?

I don't have the formula?, but I will say this, this is assuming a perfectly balanced crank!, I have seen first hand examples of a reciprocating assembly spinning up faster after a balance (strobe balancing tires on a truck)
A balance job should be considered for any rebuilt engine regardless of the intended use.

I think an accurate moment of inertia is going to be kind of difficult to get by hand given the odd crankshaft shape (although I'm sure you could split it into more simple shapes and get something close).

If there are accurate 2-d drawings (or 3-d models) It would be straight forward to model it up and get a moment of inertia for each from the CAD.