Chocolate Marble Chiffon Cake

Came across a number of chocolate marble chiffon recipe from several blogs and quite curious to know to get the marble effect. I gave it a try and was really happy it turns out well. Thanks to Grace of Kitchen Corner. I tried using measuring spoons to measure some ingredients instead of using the weighing machine and the cake is good. But I am not skillful when removing the cake from the pan. Would appreciate if readers can give me some advice.

Here I used 3 very large eggs.

Ingredients

A]
4 egg yolks [medium]
4 tbsp corn oil
4 tbsp water
1 1/2 tbsp caster sugar

B]
70 g plain flour [sifted]

10 g more plain flour
10 g cocoa powder [sifted]

C]
4 egg whites [medium]
6 tbsp sugar
1/4 tsp cream of tartar

1. Whisk egg yolks and sugar using a hand whisk till egg yolks look light and creamy and add in oil 1 tbsp at a time, whisking mixture whenever oil is added. Add in water 1 tbsp at a time like adding oil. Whisk till egg yolk mixture is well combined.
2. Fold in 70 g of plain flour then divide into 2 equal portion. Add 10 g more plain flour to 1 portion and 10 g cocoa powder to another portion. Fold in till well combined for both portions. Set aside.
3. Preheat oven at 160 degrees C.
4. Whisk egg whites with a balloon whisk in a clean mixing bowl till frothy and add in cream of tartar. Continue whisking till mixture is slightly foamy and add in sugar gradually. Keep whisking mixture till soft or stiff peaks formed. Add 1/2 portion of egg white mixture [weighs about 130 - 150 g] to egg yolk mixture. Mix till evenly combined. Do the same for the other portion.
5. Put in both mixture in 20 cm chiffon pan alternately to get the marble effect. Bake for 40-45 minutes on lower rack of oven [I used a 26 L table oven].
6. Invert baked cake immediately on rack to cool completely before removing from pan.