Flat plane crank

Severe balance/vibration issues, acceptable on a 3.0L Cosworth for couple hundred km, didn't work when they tried to use the same engine for endurance racing in sports cars.
Mopar tried to use a flat plane crank in their Prototype sports car project from the early 00's. Some W8 headed thing. They had cranks selling on racing junk a couple years back when Fiat bought Chrysler. S/F.....Ken M