Installing a new electric built in oven

I am trying to replace my existing oven with a Kitchenaid built in. Both the old oven and new one had the following wire set up:

Black
Red
WHite and ground clamped together.

However, the electrical supply is only a two wire system with white, black and a bare ground.

When I disconected the old oven, I believe it was black to black, red to the white, and the white/ground to the bare ground wire.

Do I need to run a new 3 wire 8 gage wire or can I safely use the existing wiring?

 

If it were me I would run new wire. The existing hook up took the white wire and put power on it. The stove needs 240v to work so they put power on the black and power on the white. White is commonly neutral so this can cause confusion. They then hooked up the bare to the ground and white of the stove because of the missing conductor.
I don't know if you need 8 gauge or 10 gauge...that would depend on the stove and how much power it pulls and this could also impact the breaker size.
I would go with a breaker that matches the stove, 3 conductor with a ground (4 total wires) Romex that matches all that. You can then unclamp the white and bare in the stove and land all wires separately and safely.
On the other hand...it would "work" the way it was hooked up, but not in my house.

 

Thanks. The new stove has 8 gauge. I'll go with new wire, and a new breaker.

 

You need to run new 4 condiuctor wire (3 conductors plus ground). Your receptacle needs to be four wire, as does the cord and plug. At the oven you need to separate the netural and return.