I’m fabricating a cold air base to use at the track.

First - I have seen the Engine Masters video but it doesn’t address the issue of contoured ‘air bell’ profile. A crucial omission by those guys imho.

Moving on - The 65 A990 cars ran a dual contoured air bell cold air system, HOWEVER, the 67 ‘023’ Super stockers ran a base with a much more aggressive throat ‘entry’ (see pic)

This raises the question how important an ‘air bell’ type entry is?

Any thoughts or experiences?

The hardware bridge across the top was known to be a mistake 70 years ago. 2 small coil springs can hold the plate down from underneath.
The radius shown has reached the point of vanishing returns (very little gain above 3/8": Vizard), but IDK if the filter itself is too close to the entry; another inch added front and rear might help.
The lowest pumping loss/highest CFM for a given entry has a 3/8" (or more) submerged floor, and the bell has a 3/4 (270°) rollover radius.
All of this may be insignificant on anything but a maximum effort engine.
Keep in mind that air movement in that can is not continuous, it occurs in bursts.

My theory is a radius is always better than a sharp edge. I've always used a bell on the pan or a K&N stub stack if available space prevented the bell.

I think you are overthinking it Mal . Unless you are going full in . Of course a curved entry is best if possible .
Mine is simply a chrome air cleaner base , though i trimmed it a bit for extra clearance . Why i only have a screen for racing
I know some decry a screen but it works for me

Tex

Depending on the engine size and VE, that screen may be completely neutral. As engine size goes up it will reach a point where it's a restriction.
If you attached a vacuum cleaner hose to the opening, and tried it with and without the screen, then hold a smoke generator at different places around the screen, you might see something. The vacuum engine will change pitch is loaded more, or an ammeter?

For a screen to be (nearly) harmless, use as many of these as possible:
1. larger squares (yes, it will only trap small rocks)
2. finer wire (even .5mm instead of 1/32" is better, especially if area is small)
3. larger dome diameter
4. farther away from entry vertically
5. no bracket

Polyspheric - Re the hardware bridge - do you have a pic or can you describe where you’d attach coil spring restraints?

Also, I’m not following your comment about the 3/8 radius - are you referring to the depth of the flanges?

Pick a spot on the floor of the pan, left and right sides.
Small hole, 10-24 screw, small tab (1 hole for the screw, 1 for the coil) underneath
Coil hooks to the tab
Pulls down, attaches to manifold bolt, existing linkage, any convenienet point easily reached for service

In some cases, there's enough compression height and resistance in the foam that the hood keeps the AC in place.

The flat floor of the pan is 3/8" lower than the carb's entry radius, carb will pull air from behind it. Radius in cross-section is 270 degree arc.

Minimum number of bends.. try to keep the air
flow as straight as possible.. I made a base and
used a volosity stack for mine... the stack is 5"
tall to the radius then into the carb.. lots of
air space above the carb

Ok, thx for the advice, I’ll post a pic of my fabrication shortly. I think it meets the objective

This is what I came up with. Pondering what to do for a seal now.

I have the RO23 top plate.

Looks nice.

You can get the flame-retardant foam that Moroso includes w/ their air pan kits separately from the whole kit. That's what I used to seal my plate to the hood.

The homeboy engineer in me says that's about as good as it needs to be.I have a mini velocity stack/ bell inside my carb.hat too. Don't have any A/B dyno testing but I'll believe it helps until someone can prove different.

The only way to tell if that is the best design is to run it and then remove it and try another set up
I have done some dyno testing on K&N air cleaner top elements and then the same test at the track, they didn't help on the dyno, both times I tested them on two different engine dyno both motors lost 8 HP, but at the track the car picked up .02 to .03 and right at .2 MPH on back to back (within 20 minutes) testing
I have also tested my old M.W. stocker at the track with no air cleaner base and then installed both of them with no hood scoop or air cleaner element and the car like the bases on it at the track
Test, test and test some more to keep going faster and faster until you disappear in the blinding light of exceeding light speed

Thx, I’ll look into it.

First testing will be on a dyno vs a Hemi oval dual quad air cleaner with K&N filter.

Originally I tried stub stacks on my sealed plate. It slowed down. The front carb was close to the scoop. So we milled the stack 1/2". Then it was mentioned that the bowl vents might be in a section showing low pressure. So I fabbed extensions. If the engine was getting enough air previously. And the bowl pressure was good, these probably won't do a thing. But if the motor was air limited with 2 750 Eddys or the bowl pressure fluctuated, they should help. It'll be armed with an O2 sensor in April and we'll see.
Doug

Inside The scoop. Full 2" of clearance. Same as the stock choke tower previously.
Doug