Originally Posted by andy_meng1024

Here's the whole thing looks like:
Attachment 109724

Part numbers:
Attachment 109725
Attachment 109726

With the spacer installed:
Attachment 109727

From this angle, you should see that when we talk about the area of the throttle body, the real cross section ares is not pi x r^2. It has to subtract the butterfly valve part, which means the total area is a lot less. Look at the end of the spacer, the area is not blocked by the butterfly valve at all, which makes the area almost the same with the area from the bigger throttle body.
Attachment 109728

I know this is not the ultimate design yet, which is why my new upper plenum is in prototyping already, to pair with this 80mm throttle body.