I received a speedy reply from the Cooper Works House in GB on my question about the reason to bleave the blank in the bottom. Here is Paul Cooper's reply:

Hi Henry

Thank you for your enquiry and I hope I can help to settle the debate.

The hole was included on the standard R53 in order to improve interior sound quality. In order to accentuate the interior sound of the JCW airfilter, this should be blanked. There will be no improvement in engine performance if it is removed.

Regards

Paul Cooper

 

So just like everyone's "Butt Dyno's" were correct on this matter.

 

But the JCM box has the peice removed if I'm thinking of the same blank peice..

 

I have found that the stock air MCS box flows more than enough for nearly all applications. My data shows that a CAI will bring around 3WHP above 5000 rpm. Do a head and header and things change.

 

I just had mine calibrated last week. Good thing too, mine was running 3% high.