[TomBrooks]

Your getting 5:1 to call the turn raise.

If a Villian would raise this turn without an ace one time in six, you would break even to call if your in the lead.

Lose 5 times: 5 x -1BB = -5BB
Win 1 time: 1 x 5BB = 5BB
Breakeven

If Villian would raise without an ace one out of five times, you might make a small profit to call.

Lose 4 times: 4 x -1 = -4BB
Win 1 time: 1 x 5 = +5
Small profit: 1BB in 5 hands = .2BB/hand

If Villian would raise without an ace one out of four times...
Lose 3 times: 3 x -1 = -3BB
Win 1 time: 1 x 5 BB = 5BB
Decent Profit: 2BB in 4 hands = .5BB/hand

So, would Villian raise without an ace at least one in four times?

This doesn't account for times Villian has two clubs or some other better hand like a set. It also doesn't account for having to call another bet on the river. I didn't think it through that thoroughly.