Because I have driven plenty of other cars with them. Pretty simple. I've been driving for 20 years, not 20 minutes.
Hole in piston from detonation = a lot more than $900.
As far as ring and cylinder wall wear, you're assuming I have a fuel mixture problem. I don't. Not according to my A/F gauge. Or my spark plugs. Or my vacuum readings.
Yes, I'm smarter than at least a few factory engineers. I know that for a fact, because I went to college with more than a few engineers that now have that title. Scary to think some of the guys designing your airliners only managed a "C" average isn't it? Well, they did. Average graduating GPA for engineers at UCLA was a 2.7 when I was there. And that's the 8th ranked public school in the world. Go figure.
Designing an ignition system for one of these cars is a piece of cake, and can be done by pretty much any undergrad engineering student with the proper motivation. Heck a points system could be done by anyone with an E&M physics course and maybe the first EE circuits class. They were invented by guys that had neither. Electronic would need a couple of EE classes, but nothing fancy.
And I have in fact tuned quite a few vacuum advance distributors, so, no, I will not ever come back and tell you about how amazing it was to realize how right you are. Because you aren't in this case. I've tuned 3 different dizzy's for that Challenger, with custom advance curves, welded advance plates, tunable vacuum advance cans, even the fully adjustable aftermarket stand alone unit it has now. The works. When the vacuum advance is hooked up, the old girl detonates under mid-throttle acceleration. Doesn't matter if its a can with 10* advance or 20*. Don't know why, doesn't make any sense. Same as I don't know why a stock as a clock low compression stock-cammed 318 wants 20* of advance at idle. Shouldn't, but it does. Runs better, pulls better vacuum, gets better mileage, all of it. And yes, I checked TDC and marked the balancer, thank you very much. It bugged me for awhile, but I got over it. It works, I don't screw with it, I drive it.
Well first, the shroud for the electric fans on the back of my radiator covers the entire core, so, when the fans are on, they pull air through the entire 26" radiator. Funny how that works. :D
But you want to talk about airflow through the front. The grille on your car is bigger than the gap between your hood and cowl. So, that means that all that extra air has to go through the engine compartment and out under the car. At freeway speed, the air in your engine compartment isn't that hot because there's air moving through it at not much less than freeway speeds. But, that's still thinking with a linear air flow model. Realistically, the air going through the radiator isn't laminar, it's turbulent. Just like the air coming off the edges of the opening in the radiator shroud. Which means that although the speed of the air going through the 1.25" of fins that are partially obscured on either side by the radiator shroud opening is slower, they're still seeing air flow because the radiator shroud isn't in direct contact with the fins. The air coming off those edges would look like an eddy in a river, and will circle in behind the shroud. Slower, but still moving.
And the 15% thing is false science. Yes, that's the decrease in surface area exposed to air moving at the full velocity. But it sure as heck ISN'T the decrease in efficiency. You'd have to calculate the speed of the air that's going through those fins to know that. And then that would also be velocity dependent, so it would change at different speeds. And since there are really only empirical formula's for calculating turbulent flow, you'd pretty much have to put my car in a wind tunnel to figure it out. Or model it with some really expensive software.
Yes, the air flow and the velocity is reduced to that section of the core. So, the 26" radiator in front of the 22.5" opening is not as efficient as a 26" radiator in front of a 26" opening. But it will still cool better than a 22" radiator in front of a 22.5" opening. And since almost all of these cars came with 22" radiators, well, that's probably better than it needs to be anyway. It is on my Duster.
Street cars do not need vacuum advance. They need oil, water, fuel, air, etc. But while they usually benefit from vacuum advance, they don't NEED it. At all. In fact, before the mid-sixties, most cars didn't have it.
My Challenger is pertinent because you seem to think any street car without a vacuum advance can will overheat. You said they NEEDED it. My Duster with the 340 is more relevant since it's set up very similarly to the OP's car, but you latched onto the 50k miles I've driven in my Challenger because you wanted to come after me personally. The 340 in the Duster doesn't overheat either. Despite being a .060" over 340 making well over 400 hp with a 26" radiator in front of a 22" shroud.
And, I can tune a vacuum advance can. And have. And will again. But, that wasn't my point. My point was, the OP's lack of an advance can isn't causing his car to overheat. Nor is the 22" opening in the radiator shroud.