I never use cake flour because it is bleached, and I don't care to ingest any more chemicals than I have to! I have always made all my cakes with unbleached all-purpose flour and develop the recipes using a *packed* measure of flour. A packed and leveled cup of unbleached all-purpose flour weighs 5 ounces. But most recipes call for flour to be spooned into the measuring cup and leveled off, which amounts to less weight. And some recipes intend for you to sift the flour before measuring. So you have to make sure of the measuring method intended. If you use too much flour, the cake will be dry. Weighing is most accurate.

The substitution gingerroot posted is the way to go. Make sure you sift the AP flour and cornstarch together well (rub them through a sieve is the easiest way) or whisk them really well so you don't get clumps of the cornstarch that aren't integrated in the rest of the flour.

I have used the cornstarch mixture as gingerroot suggests, and it always works fine. Substituting all-purpose works too. If I'm worried about the moisture level in a cake, I just use cake syrup (http://leitesculinaria.com/59785/recipes-sugar-syrup-2.html), which I keep on hand in the fridge.

I recently made a cake calling for cake flour and subbed AP flour with the following change: For every 1 cup of cake flour I used 1 cup AP flour minus 2 T, plus 2 T cornstarch. I believe it has to do with the protein content, AP flour has something like 11% protein, while cake flour is more like 6-8% protein. The cake came out lovely and moist.

Yes, it could have been the flour. In the olden days (the '50's), I used to see recipes that called for either "1 c. cake flour or 1 c. all-purpose flour minus 2 tblsp." Sometimes it call for only 1 tblsp. reduction. I'd sift the AP flour before measuring, then remove 1 tbsp. That should lighten it up enough.

Baking is less forgiving about substitutions than cooking. Far less, actually. Try to find a recipe which uses AP flour, or buy cake flour next time.

Not sure if it was the flour that caused it to be dry. My trick for a moist cake has always been to never serve it the same day it is made and to eather crumb coat it or frost it and refridgerate for at least 24 hours which allows the moisture to redistribute. I hope this help in some way. BTW AI have used AP for cakes and not hada problem.