In my old EK4, I drove trackday with 3-point seatbelts (factory) with EK9 seats.
And I was getting crazy! in sharp turns, was almost thrown out of the seat. And I'm a big guy at 200 pounds.
So if you need to run track days, I really recommend you that you buy some 4 point. or 5/6 point harness.
Many buckles not the horizontal seatbelts enough, So happens "submarine"
Now I run with Takata harness + shoulder pads (very important !!).
Tegiwa harness bar (which is changed in an NRG harness bar now)
And seatbelts are so strapped into the floor at the rear seatbelts.