Shhhhh, I was listening to all the head scratching. Very nice summation, that would have taken a couple hours to put together only after I dug out my John Anderson texts. Nice over all discussion as well.
Improving the airflow, without screwing it up, takes a series of pre-thought out changes. You can not change one item at a time with the aim of making progessive improvements. Single changes to individual pieces often end up conflicting with each other. It is best to package together a group of alterations and then fine tune the balance.
Can you design it once, slap it on and be perfect? No. Can you make changes to a grouped set and end up with a finished package in less iterations than item by item changes? Yep. Can you eyeball it? Nope. Can you take multiple manometer readings and crunch the data, make adjustments, re-test and yeild an aimed for target? Yep. Is it fun to do? Depends on your personality type.
The data honda provided, as pointed out by Gold, is amazingly revealing in that they had to add so much front aero to gain the 40/60 aero balance for the NSX-R. The NSX it seems is a plowing pig at speed. Wind vaning with a huge static margin to keep us mere mortals safe. Wich change made the largest contribution? Venting the radiator flow over the top of the car, or sealing in the front assembly with a flat panel?
As to lowering the car, how much is reasonable? Keep in mind the roads and transitions you are going to deal with. I hate scraping, speed bumps, driveways, parking building transitions; the front overhang is limiting in stock 4x4 mode as it is. I would hate to bottom out at speed on some mountain road with shear cliffs or shear drop offs and no guard rails; going ultra fast on the open freeway is so frowned upon around here as well. Some flexible side skirt extensions gain the same results without giving up ground clearance.
