The core support of the early 2nd gen birds had a lot of gaps on the sides and top as well as large openings for the bumper supports to pass through it. I wanted to seal these areas off to keep the air out which should reduce under hood air pressure and increase the difference in pressure in front/back of the radiator which will help the radiator be most efficient.
Now those of you with early 2nd's might go look at the car and think pffft there's only an inch gap here and there and the holes for the bumper supports. However even though they're not directly open to the front of the car the cavity between the core support and the bumper/splash pan is one of (if not the) highest air pressure areas on the car. So the air is trying to get past the core support through the gaps as fast as it can. This is the same principal of why the brake cooling duct openings are placed in the core support rather than on the splash pan.
So how big are the gaps really? I added them all up, then recalculated thinking I must be wrong but no.... Imagine a hole this big in the core support letting air in!
The bottom of the core support is bolted tight to the lower edge of the splash pan sealing it. So the sides, top, and bumper openings are where I needed seals. To seal the sides and bumper holes I used 3/32 EPDM rubber sheet and pop riveted it in place. 3/16" aluminum rivets with 3/16" body washers.
To seal the top of the core support I used the same rubber but with plastic push pin fasteners for a more finished factory look. All of the seals will become tighter as air pressure increases forward of the core support with speed.
