I have a question about crankshaft overlap- the crank I am thinking about getting has a stroke of 3.893, with a rod journal size of 2.1 and mains of 2.559.

This gives me an overlap of .383 by the Wallace calculator. I plan on making around 700 horse from this engine.

This will be a Molnar crank by the way.

Will this overlap be sufficient, or does it not matter that much?

I don't think the rod journal to main journal overlap makes a hoot on how much power the crank will handle I know several well known west coast heads up engine buildes and racers that use the Honda rod journal sizes on their big C.I. high HP BB Ford and GM builds with no disasters that I know of due to no rod journal overlap
I can remember seeing on here when that was the favorite engine theory thing to argue about, not so much now
IHTH

Cab Thanks. I have read that it doesn't matter, I have read that it does. I figure for what my engine will make I am small potatoes anyway.

Wallace's calculator provides the easy but misleading answer.
For the engineering model used by Detroit, read my comments here: http://victorylibrary.com/mopar/journal.htm

There are obviously lots of factors that go into crank strength (material, design, etc…) But without a doubt journal overlap creates a layout and geometry that leads to stronger cranks by design.

You still need to connect the main and journal pins with material, but the shorter/wider beam that connects them, the stronger the crank will be if all other conditions are kept equal.

I have to say I think a testament to this is the stock 1991 cast crank in my car. Standard journal 360 crank 2.81” with 3.58 stroke and 2.125” rod pin. This means .677” in journal overlap.

I have most definitely detonated/flexed/abused my poor crankshaft HARD… It’s been together now for 5 years, and 3 sets of worn out main bearings (from flexing). Checked it this time for straightness and it was DEAD NUTS. I would think at mid/high 9’s at 3700lbs+ it is making good horsepower, but considering it’s shifted at 6200 it makes a TON of crank abusing torque at low RPM.

Is Tom having a custom grind made for you? Is it based on their 3.91 6 bolt crank?

I think you will feel a lot better about this if you take a look at an even fire buick v6 crank. These guys are laying down some real power with split rod journal cranks. There is only a small football shaped connection on the rod pins.

Thanks guys, no the crank is not a custom grind, just one from the Molnar website.

The original Buick V6 was made from the front 3 pairs of a 90° Buick small block V8, and notoriously "nervous".
Compare from my site: http://victorylibrary.com/mopar/m-table-c.htm#B6
The even-fire retains the V8’s 90° cylinder bank angle, and offsets the paired pins by 30° - not subtracted to make to 60° (intuitive, but wrong), but added to make to 120°.
???
720° / 6 cylinders = 120° firing interval.

All modern V6 engines have a 60° bank angle (to reduce width across the banks, while increasing height) and have 60° (yuge) pin offsets.

For those curious about the actual engineering measurement, I've written an Excel w/s that inputs variables and solves for the area automatically, e-mail me for a free copy: sales@victorylibrary.com.

polysperic, Thanks so much for the info and I will be sending for your excel. Thanks!