Divide the eggs into two bowls, the whites on one side, and the yolks on the other.
Whisk the egg whites until stiff, adding the first 170 g sugar mid-process, to obtain a firm and shiny meringue, then transfer everything to the refrigerator; whisk the egg yolks with the remaining 170 g sugar, to obtain a light and foamy cream.
Pour the seed oil into the egg yolk cream, mixing with the electric beater until it is well blended.
Sift the flour and cocoa into the cream, then add the water a little at a time until you have a smooth and uniform dough.
Gently blend the whisked egg whites into the cocoa mixture, with an airy movement from top to bottom, constantly turning the bowl.
Now that the dough is ready, pour it gently into the chiffon cake mold; the mold should absolutely not be greased with butter or coated with flour.
Bake the chocolate chiffon cake in a conventional oven preheated to 180° for 55 minutes.
Take the chocolate chiffon cake out of the oven and turn it upside down on the appropriate feet of the mold, so that the cake is cooled upside down. I know it sounds strange but trust me, it is necessary.
When the chocolate chiffon cake is completely cold, gently remove it from the base of the mould, and store it well wrapped in foil until ready to serve.