Self-Directed 401k Loan --Maximum Allowable Interest?

[Ken Sanders]

I'm looking to take out a loan from my self-directed 401k, but I'm curious as to what interest rate to charge myself. I actually want to charge myself as much interest as possible since I'm not planning on contributing anything to the 401k this year. Anyone know if there is a maximum allowable interest rate and, if so, what it is?

Also, I have several different investments in my 401k in addition to cash. My plan documents state that I can borrow $50k or 1/2 of the vested balance, whichever is less. Does the vested balance include the value of my investments. Or, is it simply the amount of all of my contributions to the plan since its inception?