Ive got an F23a manifold for my F22b swap. I took the manifold apart so see if I could polish or port it (something I want to learn). however, I've never seen a manifold like this. There are four runners and next to them a huge opening. Should I block off the opening? What is it used for and what's the best way to extract the most out of this manifold?
thanks
picture : https://s31.postimg.org/56s0ftzbv/image.jpg

 

That is part of the plenum volume. Runner length and plenum volume are calculated to enhance the engines designed power curve.

Runners are tuned to a length/cross section that enhances the torque of the engine. This is initially dictated by design requirements and ultimately cam shaft profile.
Since the runners had to be a static size, they are sized to better match the cam profile to boost power in the desired rpm range.
On a street car, runners are usually long and have a small cross section, this promotes low to mid range power by keeping air velocity up at slower speeds. A short large cross section runner would promote higher engine speeds to allow better breathing.

Plenum sizing contributes to engine performance as well.
For a street car, the plenum should be kept as small as possible to promote low speed power, but not so small as it will choke the engine in its desired rpm band.
Ideally the plenum will have enough air volume equal to the engines displacement to be able to feed it enough air.

Closing off that part of the plenum would most likely hurt performance, even on a stock engine, unless you only plan to idle the engine.

Honda built that intake manifold with added plenum volume which is folded over onto the side of the runners. This was done to save space underhood while maintaining a desired volume.

 

Awesome, thank you for the info! I'll just try to clean it up and polish it the best I can.

 

That being said.... If you have the supporting mods. I.E. an aftermarket camshaft, ported head and larger exhaust. You could remove that divider for added volume. There are a number of F23 swapped CB and CD accords running gutted F23 intake manifolds with good results. On a stock F22B1/2 probably won't see much of an increase in power, but a better throttle response and a slight change to your power curve/range.

 

YES! What they said^^^ lol! Seriously though. But when it comes to the benefits of the F23 IM on a F22b1/2 it's all been mostly speculation, and the benefits of PnP'ing said manifold was even more so.... until recently... check out this link (dyno graphs are near bottom of the page, but the whole page is worth the read):

http://www.hondasociety.com/board/sh...153841&page=17

Now when I did mine I only did a very mild PnP with no before and after flow tests etc. I also had gone back n forth with Beans on the possible benefits of completely gutting that section of the plenum and decided I wasn't going to be the guy to test the theory. Well.... now I kinda wish I did?