Is this a suitable vent?

I have a 101 year old home, which I just bought. The kitchen sink has an S-Trap, but drains through a 6' length of pipe (starts as 1 1/2" and quickly, right below the floor, changes to 2") into a 4" drain line. The 4" drain line has a 2" vent just 6' back upstream... is that a suitable vent for the kitchen sink? Or do I need to install a Studor vent to be safe? Thanks...

Oh, and attached is a crude drawing of the scenario...

"S" traps do NOT have vents no matter where any other vent might be. You need a Studor AAV at the very minimum.

Gotcha... I thought that a vent upstream might alleviate the siphoning problem. Guess I'll go with the Studor instead.... thanks