My experience. When I first went to twin electric fans. I too struggled with heat. I had purchased a set of Flexalite fans with the built in, low flat shroud very similar to what our OP has on his car, and what he is looking to replace them with. (This seems strange to me).
If we look at the built in shroud of the factory C5 fans or the Lincoln fan that many use we can clearly see this is not a flat pan.
I've not heard of a single person with any type of Hot Rod or Corvette ever claim they had cooling issues with the Lincoln fan or the C5 Corvette fans. They really work. They really flow well on the highway without the need for the fans to run.
When I had the flexalite system. It worked, sort of.
My fans would run on the highway. And if they stopped running, I started getting hot! They ran almost all the time. Which created other issues. And was a constant load on my alternator. I burnt out 2 sets of flexalite fan motors over about 7 years. I then tried the ebay spal copies. But mounted them to my flat pan style shroud that my flexalite's had been a part of. Those really were poor.
A very inexpensive set of C5 fans from a crashed C5. And my fans almost never run. And when they kick on they don't just hold the temp like the flexalite's with the flat pan shroud, I can actually watch the temp coming down and the fans shut off!
I'm telling you, some people make those flat pan type shrouds work. Some. But No one has trouble with the factory type shrouds and fans.

 

That could be a problem

 

Its the same layout as the C5 fans so many are using with no issue, once he gets the flap to work as they should and suck closed then the shroud should pull from the entire shroud surface area. I do think the fact that the fans are such low power compared to the better OEM and performance type does not help.

 

I 100% agree. I will be replacing with higher flow cfm fans over the off season.

 

79, did you ever mention whether or not it overheats at idle?

If it only overheats while cruising then I'd say to block off that gap I mentioned before spending $$$ elsewhere. You could test for the price of $5 in pipe insulation zip tied into that hole.

 

It overheats both at idle and driving. I've added foam around around all 4 edges, and blocked off the cutouts but I haven't got a chance to take it out yet. The wifes got me building a sauna and adding a 36" long fire table beside the hot tub lol. I'll be taking it out tomorrow. The weather has cooled off a fair bit which is good and bad for testing. I'd like to know what it does in the heat. I'll post any progress. But I feel the fans are just too weak.

 

I agree your fans are weak. But also feel the flat pan style shroud, flaps or not, doesn't flow well enough.

 

That flat shroud is going to create a little bit of restriction to airflow. And because of that, the air will flow over the top of the radiator instead of thru it. At speed.
You ABSOLUTELY need the large FOAM SEAL on TOP of the radiator that seals to the HOOD. So the air can not go over the rad.
4 vettes has one in his pic.

You almost have to stick your head in there where the headlights go and thin like air. Where could I go that is not thru the rad?
That should solve your at-speed issue.
The idle issue is fans are too small, or too close to rad, or both.

 

Walmart has a 2" (?) square foam strip for sealing air conditioners that works pretty decent at the top of the rad.

 

The Corvette vendors sell the correct shaped foam seal for the top of the radiator support that actually fits correctly and doesn't look like you bought it at Walmart.

 

As I'm sitting at home healing as it were. I thought I'd walk out into the garage and try to take a better picture of that upper seal that seals to the hood.

Note the unusual shape to this foam seal so it matches up perfectly to the hood. Also note the section of foam seal glued to the underside of the hood. I actually purchased 2 of these seals, cut the center section out of one and glued it in to match up with the lower as I have a aftermarket high rise hood. And it works.

Right hand side of the seal

Another angle of the right hand side upper seal. Note how it's not just a consistent thickness it entire length.
And Yes, Leigh is correct, stick your head up in there just in front of your front spoiler. Look! See any gaps! Fill them!
I really did try a flat pan style shroud on my car. I really have had 3 different types of fans. I really have gone through ABSOLUTELY EVERYTHING when it comes to keeping my engine cool. I did finally win the war. My car keeps it's cool in tropical Queensland heat! But Boy oh Boy was it a learning experience!
So, I really am trying to point you in the right direction.

 

All engines look the same with the hood closed.

Also, no, the Corvette vendors do NOT sell the correct shaped foam for the OPs car. His 79 came with the stock over-the-radiator CAI intake (single for L48, dual snorkel for L82), which is now missing. Without that piece, or a pool noodle, or some foam from Walmart, there will still be a huge gap. Hopefully the OP has fixed it on the cheap, without paying the Corvette tax for an incomplete set of foam.

EDIT: Also, @4-vettes, shouldn't your radiator be centered in the radiator mounts? It appears you have the (correct) stepped radiator top, but not the stepped rubber piece that goes in the bracket.

EDIT 2: Here's a link to the piece that you might need:
https://www.topflightautomotive.com/...yle-radiators/

I'm assuming you don't want to make your own piece using foam from Bunnings.

 

These photos are from some experiments I ran a few years ago. Turns out I used pipe insulation from Home Depot (which is like a Bunnings, but orange). You can see the dual-snorkel CAI inlet over the center of the radiator, and some of the car's original 40+ y.o. foam, original radiator, and dual-Spal fan.

https://www.corvetteforum.com/forums...d-control.html

 

On my car originally I had a cold air intake in the center as well. It's a simple matter of just ordering the seal for a earlier car that didn't have the plastic cold air intake.
And yes, that will fit his 79. As per my Champion radiator fitment. Yes it has the upper rubber mounts. Yes they are correctly installed. As this is a radiator for a earlier car. The mounting is not all factory. The lower mounts are custom made. The upper mounts have been rewelded and adapted. But thank you for caring.
Yes you are correct, they do all look the same with the hood closed.
Some of us think they should look nice with the hood open. And I notice at car shows a lot of people take it way beyond that. Mine. I'd consider to be just OK.

 

Yes thats what I was also trying to say above. Theres a larger gap there seal or no seal than normal or at least it seems that way from the photo. almost as if the radiator is shorter than the stock size used for the car.

I didnt have the foam seal between the hood and rad support in the top picture shared above. I added it later (lower photo) and in my case it didnt have any effect that I could actually see but common sense would state it could force a decent increase in air through the rad.

The spal dual fan type shroud im running is even shallower than the ops aluminum shroud and I have no issues so im inclined to thing his shroud will work great with better fans and good seals myself.

 

You guys keep referring to flat pan shroud. Mine is no different than what i see here. Has a 1" lip all the way around.
As for that gap or gaps between the hood and radiator, I will be addressing that for sure. I have added foam around all 4 edges sealing it to the radiator. And closed off the cutouts.

 

I think you'll be fine. I think the issue at speed was the lack of foam/CAI intake, and the issue at idle was the underspec'd fans (though a bit more timing might help, too). You do have the lip spoiler under the car to direct air into the radiator, right? It was redesigned in 1980, but is absolutely critical in 79.

Can I ask where you got that pan? Did you bend/weld it yourself? Again, I think that shroud is fine, and I'm looking forward to hearing the road test results.

 

The spoiler is there yes. Someone here mentioned there's an extended spoiler. I'll be looking into that as well.
I personality didn't fabricate the pan but I designed it and had a buddies shop whip it up for me. Basically after the C5 shroud.

 

Yup, and I still don't like it. The C5 shroud has a lot of draft, (angle) to it to facilitate flow.