They are almost the same save for a few things. Like the port size, the 25 is bigger than the 20. And the manifold won't bolt up to the Rb20 head. I looked into seeing if I could mod the greddy Rb25 intakemanifold onto the Rb20 head. It wasn't worth it. Could have been done but I passed up that Idea and bought a intake manifold off some guy. it's on my Pics page.