Engineering360: "Watch how efficiency, emission gains drive diesel engine simulations"

My 1975 VW Rabbit had piston bowls. He head was basically flat with the valves tucked up in a trapezoidal cavity in the head along with the spark plug.

Guaranteed piston to valve clearance if you broke a timing belt. Even after I had the head shaved 40 thou. The dished pistons had a squish zone around the perimeter that forced the charge towards the center of the chamber as the piston neared TDC.

That little 1.5L liked to rev and had some nice scoot once I bumped up the compression. That in a car that barely weighed 1,500 pounds.