[Tex/LaTex] Change Font Size in Chapter Title without affecting Running Headers (Book Class)

Question

Actually, I'm using the bookest class but it inherits book class commands. The documentation is sparse, unfortunately, and CTAN's book class manual seems to be misfiled (downloading the documentation from the book class reveals a pdf about writing classes in general).

I would like to change the font size of the chapter title without affecting the size of the running headers. There has to be a simple way of doing this.

For:

\chapter{THIS CHAPTER TITLE IS TOO LONG}

substituting:

 \chapter{\huge THIS CHAPTER TITLE IS TOO LONG}

affected the running headers.

Answer 1

Or with the package titlesec. This allows to change the format in a way more flexible.

\documentclass{book}
\usepackage{titlesec}
\titleformat{\chapter}[display]{\bfseries\huge}{\chaptertitlename\space\thechapter}{20pt}{\huge}{}
\begin{document}
\chapter{THIS CHAPTER TITLE IS TOO LONG}
Text
\chapter{THIS CHAPTER TITLE IS OTHER TOO LONG}
Text\newpage Text
\end{document}